MARINE)
PRACTICAL
KNOWLEDGE)
ELECTRICAL
Third Edition)
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IS>
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Denn'is
T. Hall
SA (Hans),
CEng MIEE,MIMarE)
\n,
WITHERBY
Seamanship
INTERNATIONAL)))
IS>)
MARINE
PRACTICAL
KNOWLEDGE)
ELECTRICAL
Edition)
Third
Dennis T. Hall
BA
(Hans),
CEng
MIEE,
MIMarE)
\n\n
WITHERBY
Seamanship
INTERNATIONAL)
Witherby
Seamanship
A Division of Witherby
4 Dunlop
Tel
Email:
Square,
Livingston,
No: +44(0)1506463
info@emailws.com
International
Publishing
Edinburgh,
Group
Ltd
EH54 8S8, Scotland,UK
227 - Fax No: +44(0)1506468999
- Web:
www.witherbyseamanship.com)))
1984
First Published
Second Edition
1999
Edition
2014)
Third
ISBN: 978-1-85609-623-2
eBookISBN:978-1-85609-624-9)
@
British Library Cataloguing in Publication
record for this book is available
A catalogue
Dennis
T. Hall
2014)
British
Library.)
Data
from
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No part of this publication may
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the authors and the publisher
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in any
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Printed
\n
\\-,\\HEl?\n
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\nI
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Great
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.- \",..)
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...-6
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0 \no
\n(
ISlJING
Published
by
Witherby
Publishing
Group
Ltd
4 Dunlop Square, Livingston,
Edinburgh,
Scotland,
EH54
8SB,
UK
Tel No: +44(0)1506463 227
Fax
No:
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999
Email: info@emailws.com
Web: www.witherbys.com)))
by Bell & Bain Ltd, Glasgow
or
or otherwise,
of
made in
kind
any
reliance of any
Preface)
This book's objective is to
applications
marine
help
and
electrical
and operational level endorsements
can
be found on board ship.)
for management
that
engineers acquire the knowledgerequired
and to become
more familiar
with
various
The systems are explainedin terms of their operating principles and safe working
and
faults
are considered
and significance of various electricalappliances,circuits
troubleshooting practiceis examined.)
A
wide
range
along
ancillary electrical services are described,
care and maintenance.)
of onboard
battery support,
of electrical
The application and operatingprinciples
practice, safety procedures and testing methods.)
will be
book
This
About the author, DennisHall
knowledge
delivery methods for
manager
colleges in Europe,
and
as
the
Head
and
marine
with
detailed
information
are examined,
as well
as
electrical
voltage
engineering.)
in shipbuilding
followed
industry, with initial
training
Officer. This was followed
and
Electrical
by design
around
the
world.
Further
and
electrical
experience
systems
and effective
Navy where he was introduced to the requirements
At
South
examined
and
high
on
an
of engineering
personnel.
training
of Electrical Power Systems, he
USA
type
and a common
(1940-2009)
work for large power industrial
was acquired in the Royal
inspection
The
practice.
STCW
level marine engineers, electrical
engineersand
operational
Hall had long experience with the marine
as
in the Merchant Navy
experience
practical
Dennis
by
and
management
students currently studying
well as
as
electricians,
to
helpful
propulsion
by
electrical
Tyneside
many
ship
as a lecturer,
College,
visited many marine
and
types
Japan.)
the training and education needs of the marine
to meet
industry and this book has, for
been the mainstay. The technicaleditors of Witherby
Publishing
Group have been careful to
while
of
Dennis'
book
has
been
and informative
the straightforward
maintained,
bringing
style
Dennis was driven
many
ensure
years,
that
additional
material that
updates
and
expands
the subject
matter.)))
in
Contents)
Preface
Chapter
III
One)
Ships'
1.2
Electrical
1.3
Electrical Safety
Chapter Three)
Chapter
Four)
Safety
and
Maintenance
1
2
Calculations
3
7
7
Diagrams
Electric
Shock
8
Resistance
1.5
Insulation
1.6
Circuit Testing
1.7
Two)
Systems,
Circuit
1.4
Chapter
Electrical
1.1
10
10
Insulation
Testing
1.8
Continuity
Testing
1.9
Multimeters
1.10
DiodeTests
12
12
14
1.11
Current
1.12
Live-Line
1.13
General ElectricalMaintenance
15
1.14
Fault
Finding)
17)
Distribution
19
Electrical
Clampmeters
14
Testers
15
2.1
Power Distribution
2.2
Insulated
2.3
Significance Earth
2.4
Distribution
2.5
Transformers
2.6
Instrument
Transformers
2.7
Shore
Supply Connection
2.8
Circuit
Protection
2.9
Electric
19
System
and Earthed Neutral Systems
Faults
of
28
Circuit Breakers
29
32
33
36
Cables)
44)
Circuit
Main
and
Generators
22
24
Breakers
3.1
AC
3.2
Generator
3.3
Construction and Cooling
Excitation
Methods
3.4
Automatic
Voltage
3.5
Generators in Parallel
Generator
Operation
Regulation
49
49
52
55
57
60
Generators
3.6
Emergency
3.7
Generator Protection
65
3.8
Generator
66
3.9
Main
3.10
Main Circuit Breakers)
Motors
Maintenance
Switchboard
and Starters
4.1
Motor
4.2
Enclosures
73
and Ratings
Induction
4.4
Control Equipment
Motor
4.5
Directon Line
4.6
Reduced
4.7
Speed
4.8
Motor
4.10
Maintenance)
Operation
(DOL)
73
76
78
Starting
Voltage Starting
Control
80
81
86
90
Protection
Single-Phase
67
68)
73
Construction
4.3
4.9
64
Motors
96
97)))
VI
Practical
Chapter
Chapter
Marine Electrical
Five)
Six)
Knowledge)
AncillaryElectrical
5.2
Emergencylighting
5.3
Refrigeration
5.4
Cathodic Protection
5.5
Battery
Understanding the Fire Triangle
Atmospheres
118
119
121
Protection
Explosion
Exi
6.7
Exe Increased
6.8
Exn
6.9
Exp Pressurised
6.10
Exm Encapsulation
Intrinsic
122
Enclosure
Exd Flameproof
123
Safety
125
Safety
126
Non-Sparking
Apparatus
Operating
Electrical
Class Rules for
Tankers
and
Installing
Systems
6.12
Additional
6.13
Electrical
Areas
Testing in Hazardous
Maintenance
of Exd-protected Apparatus)
Periodic
in
Hazardous
Areas
126
126
126
128
128
128)
131
Requirements
Survey
117
117
Tankers
ExplosionGroups and TemperatureClasses
6.6
7.1
SOlAS
7.2
Classification
7.3
Main
7.4
Generators
7.5
Circuit
Breakers
134
7.6
Switchboards and Fittings
135
7.7
Cables
7.8
Insulation
7.9
Motorsand Starters
7.11
7.12
7.13
7.14
131
Survey Items
Electrical
132
135
Resistance
Parts of Steering
Navigation
Associated
and
Power
Emergency
MS
light Indicators
Operation
141)
and High Voltage
Propulsion
Power Supply Network
8.3
Review
8.4
Controlled Rectification and Inversion
8.5
Converter
8.6
Propulsion System Operation
COSWP
of
Motor
146
148
Operation
Types
Harmonics
Auxiliaries
Propulsion
High
Voltage
on
High
Voltage
Safety
High Voltage
its
and
Protection
Ships
Equipment Testing)
to Work)
143
143
Scheme
Propulsion
Perm
138
139
8.2
8.11
137
137
137
140
Electric
8.9
8.10
Equipment
Gear
Tankers)
Electric
8.8
132
Governors
and
U
131
Societies
8.1
8.7
Index)
on
Zones
6.5
7.10
Appendix 1
for Hazardous
Practice
6.2
6.14
Chapter Eight)
109
112)
Hazardous
6.11
105
Supplies)
6.1
6.4
Seven)
102
Air Conditioning
and
Electrical
Special
101
Signal lights
Navigation
6.3
Chapter
101
Services
and
5.1
151
152
158
161
163
166
168
171)
175
185)))
Chapter
One
Ships'
Electrical
and
Safety
Systems,
Maintenance)
on
services
Auxiliary
board
ship include thrusters,
room
pumps,
cargo cranes,
engine
and fans, deck winches and
poweris usedto drive
auxiliary
and
operating
as
nearly all
emergency
event of a main
power system
a secure
distributed.
An
generator
emergency
switchboard
maintain
supplies
and
in the
failure.)
power
supply to all
built-in protection for the equipment
personnel.)
The general
system,
majority
provide
then
of these
electrical
should
have
loads
and
the
The
services.
on board ship
general
and air conditioning. Electrical
catering
lighting,
compressors
windlasses,
The main AC generators
called
(sometimes
the
electrical
power,
alternators) produce
which
is supplied
to the main
switchboard
and
scheme of a ship's electricalpower
in Figure
1.1, is common to
shown
may be driven
by a diesel
a
steam
or
or by the main
turbine,
engine, by
gas
as
a
shaft
The type
propulsion engine
generator.
of prime mover is determinedby the design
of the
and
economic
factors.)
ship
by
The generators
ships.)
Emergency busbars)
Main busbars)
/II
/II)
III)
Q1
M
M
Q2
ctr\\\n
-@
Q3
ctr\\\n
M
QE1
ctr\\\n
-@
M
QE2
ctr\\\n
-@)
-@)
SG busbars
M
ctr\\\n
-@)
Main
Emergency
consumers)
consumers)
/II)
Q4
$111
M
$111
ctr\\\n
-@)
111)
111)
Non-essential
Non-essential
consumers)
consumers)
400kW)
3 x 380V, 50Hz
400kVA)
Figure
1.1 - Electrical
3 x 380V, 50Hz
400kVA)
power system)
3 x 380V, 50Hz
900kVA)
3 x 380V, 50Hz
400kVA)))
2
Marine Electrical
Practical
combined
The
rating of the generators is
demand
from the ship's
power
determinedby the
electricalload.)
Knowledge)
The
the powerdemand of the
whether at sea or in port,
registering authority.)
Hz).
or as
required
kV, 6.6
(3.3
high
voltage
of normal
fault
current.)
The
British
kV
or
11 kV)
Commission
to 1000
to harmonise
definition
Lighting
and
usually
operate
other
to limit
\n
the
a large
3.3 kV
a 440 V switchboard
Batteries
24 V DC.)
for essential
+ \n + ...(in
+ \n
\n
R 1
LI'N
==
(in
R 2
series)
parallel)
R3
Law)
(Kirchhoff)
Ll oUT (Kirchhoff)
P==Vx/==[2xR)
British and European
V. Single-phase
equipment
R 2)
V == I x R (Ohm's
Example:
AC
V (440
V)
Using the above circuit with a 110 V DC
supply and R 1 == 6 0, R 2 == 5 0, R3 == 5.5 0,
calculate
all currents, supply power and pd
across the 6 0 resistor.)
is to be used in
hot and damp locations, it is advisable
at 48 V, or even 24 V, supplied through
of a step-down transformer. Occasionally,
are
also used to step-up voltages,
eg to supply
==
RT
at a
to operate
transformers
R3)
V2
(lEG) definition of low
V AC (the IEC gives
transformers are usedto reducethe 380
system to these lower voltage levels.)
portable
R 1
R T == R 1 + R 2 + R3 + ...
low power ancillary services
at 220
/2)
V
(BS) and International
Standard
standards).)
use
V1
Lemfs == LPds
Electrotechnical
the
+/ 2
/1
load current and the prospective
voltage is 50 V AC
dangerous,
1
by the
that operate
generators
require
size
Where
/=/
440 V,
with a very large electricalpower
Ships
demand will
this
for all situations,
DC circuit)
on board ship is commonly
power
at 380 V, 50 Hz (sometimes
generated
60
load
and
circuits
of DC and AC
is a brief revision
calculations.)
following
Large
passenger
ships usually have 4 large
r
ated
at 10 MW or more, to supplythe
generators,
electricpropulsion
motors
and the hotel services on
board.A cargo ship may have two main generators,
rated
from 350 to 1000 kW,
which
are
typically
sufficient to supply the engine room
auxiliaries
while at sea and the cranes for handling
cargo
while in port. The limited load consumed during
an
means
that an emergency generator
emergency
be rated
from about 50 kW for a small coaster
may
to about 300 kW or more for a container ship. The
must
estimate
the number and power
shipbuilder
of
the
rating
required
generators
by assessing
Electrical
Calculations)
Circuit
1.1
overall
bow
thruster
motor
from
supply.)
services operate at 12V or
Determine
/ 1 == 110/(6
as,
+ 5) == 10 A and
12 == 110/5.5
so supply
current is I == 30
A
== 20
Supply
power is P == V x 1== 110 x 30 == 3.3
[check
with P == L(12R)]
pd
/
1
(potential
x 6 == 10
difference)
x 6 == 60
V)))
A
kW
across 6 0 resistoris
Electrical
Ships'
/ = /1 + /2
circuit
AC
Single-phase
AC circuit)
Three-phase
'L)
(phasor addition)
t
Safety and Maintenance
Systems,
/1
' L)
/2
V
R,
\\1,.3)
V
.1
I
+
I Z1
f
\\1,.3)
R2
R2
l
\\1,.2)
,)
Z2
I
XL
Xc
Vci
(L)
(C)
J
I
V
L
X V
== \n3
IL == \n3 X IpH (in
VL == V pH and
== 2TTfL
XL
(0))
==
Xc
112TTfC
Z=
or
\n R2+X/
==
PpH
(0))
Balanced
Z=
IL == I pH (in Star)
and
pH
\n)
V
pH
X I
X
== I
coscp
pH
P == \n3
three-phase:
pH
Delta))
2 X R)
X V
L
x I
X
L
coscp)
\n R2+X/)
I == V/z
factor
power
==
== R/Z
coscp
== PIS
or lead)
(lag
Example:
P == V x I x coscp or P == PR
V x I x sincp
==
Q
or Q
S == V x I or S == PZ
== PX
(W)
Using the above circuit
(VAr)
440 V, three-phase,
60 Hz AC supply
and ZpH == 10 0 at pf == 0.8 lagging
(VA))
Calculate phase and line currents
power when connected as:
(a) Star
with
a
Using the above circuit
220 V, 60 Hz AC supply and R 1 == 6 0,
R 2 == 5 0,
L == O. 1 H, C == 1 00
IJ F
all currents, supply power, overall
and pd across the 6 0 resistor.)
factor
power
as,
(a) in
Star,
V pH == 440/\n3
so IPH
== 254110
Then
Z1
== 27
and
Z2
/ 1 == 220138.2
So,
and
1 == 220127
2
The
total
supply
which
must
0 at
== 38.2
79.3
0 at
== 8.15
0
and
(leading)
A lagging
== 5.76
V by 81\302\260
V by 79.3
A leading
V
pH
0
current is the phasor sum of
A
A also
==
V
L
== 44
IL == \n3 x 44
supply
V
x 25.4 x 0.8 == 15.49
x 440
so IpH == 440110
81\302\260
(lagging)
== 254
== 25.4
IL == I pH == 25.4
(b) in Delta,
0
== 26.5
and
Delta)
(b)
as,
P== \n3
and Xc == 112xTTxfxC
TTX fx L == 37.70
== 2x
and
Determine
and
Determine
XL
a
load).
(balanced
Example:
Calculate
with
==
76.2
== 440
kW
V
A
A
x 76.2 x 0.8 == 46.46
P== \n3
x 440
(notice
this power is three timesthe value
in
kW
star))
/1and 12
be resolved into
and 'quadrature'
(horizontal)
'in-phase'
(vertical)
components before adding.
The
1==
Supply
Power
result
(for you
3.34
A at
power
pd across
to check) is
with
P
==
W
L(J2R)])
factor is cos43.8\302\260
60== / 1 X 6 == 5.76
== 0.72
Electrical
Diagrams)
Symbolsare used to represent
43.8\302\260leading
== 531
is P==220 x 3.34 x cos43.8\302\260
[check
Overall
1.2
leading
x 6 == 34.56
V)
the
different
items
of equipment in a circuit. The shipbuilder will have
a complete set of electricaldiagrams
provided
and
it is important
that you study them to be able
to read,understand
use them as an aid in
and
locating
electrical
faults.)))
3)
Marine Electrical
Practical
4
A block
shows,
diagram
Knowledge)
in
form,
simplified
the main
NEMA,
etc)
The use of a circuit
represents
in
operating
clear
enables
and
to follow
followed
by
to
personnel
each sequence
operation
that
in
faulty
has
failed.
operation
involved
The components
can then be examined
to locatethe suspectitem.Thereis no
the main features of a system
and its
use
is to illustrate the ways of
the system.
Details are omitted to make
as
the same
power
bounds. Its main
the diagram
meet
on the
from the moment of turning
the
operation
(eg by
supply and initiating
to the final act (eg starting
pressing a start button)
If the
of the motor).
fails, the engineer
equipment
until he comes to the
can follow the sequence
the
in
1.3,
Figure
electrical
represent
diagram
understand the circuit
operationthat
as shown
diagram,
power
symbols that
component
each block,but usually
do not give any information
about the componentsin each or how they are
interconnected.)
A
for the
components,
you must be prepared to
various
different symbols representing
on the standard
depending
manufacturer.)
the
equipment's
of
elements
interrelationships between the major
or may
the system and how the system works
be
to depict
used
operated. Such diagrams are often
control systems and other complexrelationships.
The
block
in Figure 1.2 describes the
diagram
main
functions
of an overcurrent
relay (OCR) used
to
the motor starter. Its circuit diagram
protect
shows one way of realising the overall OCR
function. Diagramslike this state the function of
examine
other components
are
that
need
to
known
to
no influence
function correctly and have
so the work is simplified. A circuit
fault,
an essential tool for fault finding.)
as possible.)
circuit
such as Figure 1.4, showsthe
diagram,
detailedfunctioning
of a circuit.
Graphical symbols
are arranged to show the operation as clearly as
to their actual physical
possible,without
regard
layout. The coil and its related contactsare
on the
diagram
is
A
identified
a number
international
by
are
there
CT)
diagram shows the componentsin the
the
actual
positions
they occupy within
The components are shown complete
enclosure.
and
are
represented
by a block, with the
simply
terminals
necessary
clearly marked with reference
A different thickness of line can be used)
numbers.
A wiring
approximate
and letter code. Although
standards (IEC, EN,)
Input
Current
Filter)
Setting)
Time
Rectifier)
Detector)
Setting)
RLA)
Amplifier)
and
alarm)
Trip
IL)
Instantaneous
Overcurrent
Electronic
trip)
Relay (Block diagram))
R6
R5)
D3)
R7)
+ve)
Current
setting)
Time
Setting)
C3)
R3)
C1)
Inst.
CT
Setting
Input)
It)
V1)
Detector
R4
and
curve
Trip
shaping
and
alarm circuits)
circuits)
C3)
-ve)
Electronic Overcurrent Relay
Figure 1.2 - Blockand circuit
diagrams)))
(Circuit
diagram))
Ships'
1
3-
Neutral
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resistor
HV Generators)
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3 x 6.6 kV 60 Hz HV MSB)
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2
3-
Systems, Safety and Maintenance 5)
Electrical
SB section)
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Main distribution
Main distribution
Transformers)
transformer)
transformer)
Converters)
Propulsion motors)
Harmonic
filter)
Harmonic
filter)
rn
Excitation
PT section)
supplies)
3 x 440V 60
1.3 - Power
Figure
SB section)
,;)
system
Hz LV MSB)
diagram)
3 x 380 1
L1
2
3
L2
L3
X1
3
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4
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3
4
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2
53
4
2
4
54
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15
3
5
3
5
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2
4
6
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4
6
A1
A1
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Figure
1.4 - Star-Delta
motor starter (power and control
diagram))))
-K1
-K2
6
Practical
to
differentiate
Marine Electrical Knowledge)
between
The
connections.
wiring
the same starter shown
power and control circuit
1.5 is of
diagram in Figure
in
simple
circuit,
the sequential
operation of the circuit.
of a wiring
is to instruct
purpose
diagram
the wiring
installer
how to construct
and connect
the equipment.It is of little use in troubleshooting
other
than for identifying
the
exact
position of
to use
and to)
suspect components, terminals and wires.)
understand
1.4.)
Figure
A wiring
diagram
may be of a fairly
but its layout makes it quite
difficult
main
The
1
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1.5 - Star-Delta
motor starter wiring
should be done if difficulties
on an item of equipment
is available?)
diagram
arise
in locating
a fault
and only
a wiring
.
time and trouble to
save
well
wiring
diagram
converting a wiring
into
a circuit
diagram
certain basic rules and
into
conventions
Every
right
\302\267each
sequence
should
convert
When
diagram.
a circuit diagram,
should
be
be drawn from left
and from top to bottom
stage
from left
to
should
right)
be in
(where
order
all
possible)
of occurrence
to
and
contacts
should
the same
that are in
components
be drawn side by side and
level to emphasise their
parallel
function
.
all
major
components
voltage should be drawn
operating
at
the
to help
(or aligned horizontally)
required components quickly
\302\267 all
of
diagram
parallel
followed:)
\302\267
in series
are
line (where
they control
that
possible) with the component
(eg contactor's coil) locatedat the bottom
the
ANSWER)
the
contacts
and components
should be drawn in a straight
\302\267all
What
may
1=11 \037I)
diagram)
QUESTION)
It
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Figure
52
mrt-)
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r\037\037 J
contacts
should
or closed,ie their
condition.)))
at busbar
level
identify the
same
be shown either open
'normal'
or de-energised
at
Ships' ElectricalSystems,Safety
block,
conventions, but
diagrammatic
are the
and wiring
diagrams
for
electrical
work.
Other
use
general
other
are
There
./
system,
main types in
to provide
used
types are sometimes
where the basic types are unsuitable
information
./
a pictorial
(eg
Diagramsshould
and
DO
inform
the duty
essential tool
equipment.)
as an
regarded
work on electrical
./
DOswitch
./
Electrical
Very
current, power,
of danger in an engineering
system.
possibility
To minimise the safety riskto personneland
must be designed and
equipment,
systems
with international
to comply
manufactured
to be
precautions
taken.)
conventions
X
X
reason
DO NOT touch
rotating
DO NOT leave
live conductors or rotating
parts
DO NOT overload equipment.
X
DO
You
NOT
societies
safety
(eg lEE),
procedures.)
potentially
serious consequences.
essential
list of DOs and DO NOTswhen working
./
electrical
Keep in mind
DO get to know the ship's electrical system
to
the
and equipment.Study
ship's
diagrams
location
the
of switches,
protection
devices and interlockssupplying
and
boards
Write
down
Become
essential
familiar
on switchboard
operation
./
with
a
notebook.
normal
according
abnormal
to the
recommendations.
equipment
manufacturer's
according
to the
recommendations or the
shipowner'smaintenanceprocedures.)
and
by the
Shock)
Electric
1.4
practices
company.)
an
Many
an electric shock
experienced
it is generally just an
it can be fatal.)
its
worst
have
people
while
and,
unpleasant experience,at
has
who
Anyone
equipment
safety
of
access
procedures
electrical
safety
the
throughout
to live electrical
fully aware
be
must
of first
aid
and
related to electric shock. Copies
should be displayed
information
ship.)
indications
instruments so that
DO operate equipment
DO maintain
the
in
be quickly detected.
can
manufacturer's
./
items of equipment.
information
this
distribution
times
and safe working
procedures
at some time
equipment:)
pinpoint
think SAFETY at all
should
implemented
etc.)
Ships' staff must operate equipmentin a safe
and maintain it in a safe condition at all
manner
with
cause
to do so will
times. Failure
danger,
operating and
Most accidents occurdue to a momentary
of concentration or attempts to violate
standards associations
Register),
or abuse
neglect
a safety conscious attitude.
This
develop
may
well save your life and the lives of others.
(eg SOLAS),
Classification Societies (eg Lloyd's
parts.
X
(eg BS
with
(by using
for any
national and international
industry
are DEAD
DO NOT touch live conductors
or under any circumstance.
loss
IEC),
before
terminals.)
and
overhauling
governmental
circuits
that
remove
supplies,
notices
X
Regulations control the construction,installation,
of electrical equipment
and maintenance
operation
as far as possible.
is eliminated
so that danger
standards
of safety are issued
Minimum
acceptable
national governments,
various
bodies,
including
by
and
for
exposed.
installed.
Before
standards and be correctly
there
are
some
electrical
work,
attempting
any
international
OOW
equipment
covers.
equipment
DOconfirm
the
create
safety
lock-off
and
off
conductors
temperature,force,pressure,etc
basic
essential
an approvedvoltagetester)beforetouching
Safety)
of voltage,
values
high
and
engineer
fuses and displaywarning
removing
1.3
tight.
down
shutting
and fixings
maintenance.)
be
out
in place
before
view of a component).)
when carrying
are
all bolts
that
and
fitted
7)
covers and doors
that all guards,
ensure
DO
are securely
circuit
Maintenance
and
shock is caused by the flow of current
to hand
hand
This is often from
body.
through
your
or from hand to foot. A shock current as low as
Electric
15 mA
(AC
or DC)
may be fatal.)))
Marine Electrical
Practical
8
Knowledge)
Resistance)
Insulation
1.5
All
electrical
of
the
is to prevent
The value
conductors.
be high enough
from conductors.
must
away
The purpose
direct contact with live
insulation.
has
equipment
insulation
of the insulation
resistance
to prevent current
leaking
Insulation resistance is
measured between:)
DANGER
Conductors
.
conductors.)
The
minimum
1.6
- Electrical
safety warning)
up.
goes
voltage
is further
This
means
shock
the
that
deposits
by the
current
The size of
at high
increased
voltages.
also depends on factors such
as your state of health, the degree of contactwith
live wires
and the perspiration or dampness on
skin.
your
Typical
dry full-contact body resistance
is about 5000 0 at 25 V, falling to about 2000 0 at
body
your
resistance
250 V.)
of leakage currents through
surface
is called tracking, which is also affected
flow
The
of shock
size
relevant register
by the
regulations.)
current is related to the applied
voltage and your body resistance. Unfortunately,
resistance
your
body
goes down as the applied
The
value of insulation
acceptable
is limited
resistance
Figure
and earth)
risk!)
shock
Electric
.
and clearance
creepage
distances between
in Figure 1.7. Equipment
in a clean
must be maintained
condition to prevent
and
to maintain
the value of insulation
tracking
resistance
above
the minimum acceptable value
shown
as
terminals,
(usually at least 1 MO
materials
Insulation
voltages
up to 1000 V).)
are non-metallic.
Insulation
for
is adversely affected
by
temperature,
humidity,
stress,
such as
factors,
and mechanical
oil, dirt and old age.)
many
electrical
chemicals,
vibration,
QUESTION)
What
be
at
the equivalent
V and 250 V?)
would
25
shock current levels
and paper. They may
ANSWER)
5 mA
of about
and
48 V and
as reasonably safe for
is why special
step-down
are used with portable
portable
below
shock
is centre-tapped
are regarded
tools. This
The majority
hand
isolating transformers
tools
and hand lamps.
voltage
to earth
to earth,
is the
material
air surrounding
the
electrical components.)
These transformers supplythe tool or lamp
at 48 or 24 V AC but, because
the secondary
winding
compounds to exclude
Other
substances.
harmful
materials includeceramic,mica,glassfibre, PVC
other types of plastics and compounds.An
used
medium
not normally considered
extensively
and 125 mA.)
as an insulation
Voltages
or resin
other
and
moisture
either
be
varnishes
insulation
cotton, silk
or
treated with
dry
include
materials
insulation
Traditional
excess
of 100\302\260C.)
is 24 or 12 V AC.)
electrical
materials
insulation
withstand
All
the maximum
of
cannot
temperatures
in
are
use
common
much
in
heats up when carrying
equipment
load current, with
a consequent
This
rise will
temperature
that
be
rise
above
in
temperature.
that of the
ambient cooling air temperature.)
is often accompanied by falling,
which
cause
additional physical injury and
may
first
If
aid.
the
shock
victim is unconscious,
require
resuscitation must take priority
over
other
first aid.
Electric
shock
Resuscitation techniques are mandatory
training courses.)
on
first
aid
marine
electrical
is constructed and
equipment
rated to work satisfactorily
in a maximum ambient
air temperatureof 45\302\260C. Under these conditions
the expected temperature rise will not exceed
the
All
permitted
temperature
limit
set
for the
insulation)))
Electrical
Ships'
It is,
material.
therefore,
the
dictates
that
maximum
temperature of the
the insulation material
permitted operating
electrical
temperature. Therefore,this
rated for safe working
Insulation
pumps
at a far
must
be
an environment.)
at which
temperature
use for
C were in general
Classes 0, A, Band
0 is now known as Y and
many years, but class
some
classes
(E, F and H) were addedto legislate
and
material
new
processes
The maximum temperature
these classes is:)
Insulation
Class
y
Temperature
allowed for
each
of
F
B
E*
A
field.)
this
in
rated motor will
temperature at which
eventually
reach
a steady
the
heat
in the
from frictional
H
with
are steady
manufacturers
for
the same, regardlessof the
and
no flow
of
cooling
considering a suitableoperating
electric
the
motor, the temperature
must
also be
hottest
in the
point of the winding
referred
to as the hot
taken into consideration,
air. When
temperaturefor
the
spot temperature.Forexample,
that
From
the
surface
near
the centre
Creepage)
..-...--.-...--..
...
..
\037.:
Distance
of insulating
Figure
hot
spot
of the winding.
there is temperature gradient to
point,
the)
of the stator core meaning that
be
across
will be
For
1.7 - Creepage and clearance distances)
of the
example:
If a motor
is tested in an ambient
temperature
or cooling air temperature of 20\302\260C, and a motor
the rise is 35\302\260C.
of 55\302\260Cis recorded,
temperature
motor is at an ambient temperature
When
the same
a total
rise will still be 35\302\260C, giving
of 45\302\260C, the
motor temperature of 80\302\260C.)
the appropriate
hot spot
class of insulations and,
determined
temperature for
the
that,
a given
surface
temperature,
the permissible
temperature riseis reachedby deducting
maximum
machine
A
motor
ambient temperature under which
will be required to operate.)
continuously
operating
with these
the
the
hot spot
of 15 to
an expected
life
have
temperatures would
that
failed.
20 years before the insulation
However,
life
expectancy
over
the
would
permissible
be halved for every
temperatures.)
Clearance)
surface
heat
temperature
..
...
..
\037\037)
material)
the
dissipated
cooling air.)
from
surface temperatures measured
stopped
equipment
in a coil will
losses
The
at the same rate as they are generated.
difference between this steady temperatureand
of the incoming cooling air is the temperature
that
this rise is always
rise.Forall practical
purposes,
Having
These
the
measuring
A continuously
80\302\260C105\302\260C120\302\260C130\302\260C155\302\260C 180\302\260C)
Class E is used by European
(*) I nsulation
marine
applications.)
by
winding or the surface
temperature by thermometer.)
arising
operate the electrical motors. It is officially called
on
Insulation Class and it is often abbreviated
as 'Ins. CI. '. Classes of
the nameplates of motors
are listed in IEC and NEMA standards.
insulation
for
either
of the
resistance
in
windings and magnetisedcoresand
to
is safe
it
The
coil.
the
throughout
9)
higher
is classified accordingto the maximum
permissible
uniform
temperature,therefore,is
change
circulating
Safety and Maintenance
only practical means available to determinethe
insulation
in such
is not
temperature
equipment.)
There are exceptions, such as oil
for thermal oil plants, that
operate
Systems,
Distance in air)))
10\302\260C
Marine Electrical
Practical
10
Circuit
1.6
Knowledge)
Testing)
,
r
This sectionlooksat the electricalcircuit testing
operations
you may need to carry out and the
instruments
you will
The main
'l
so.)
--,':io ::J\03719(E!.-,
; 021
are
tests
to do
need
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ill;l/'\037. ,
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for:)
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Resistance
I nsulation
Using a (megger) tester
V DC for a 440 V circuit)
Do not use a multimeter
for this task
500
(at
(IR)
Resistance
(Low 0)
Continuity
ComponentResistance
(AC
- Insulation
(IR) tester)
resistance
a multimeter
using
Typically
(0 or kO)
Voltage
1 8a
Figure
FLUKE1503
mlTfR
/NSU(,ArION
or DC)
.1)
a clampmeter
multimeter for small
Using
Current
(or
I)
.J
-
currents))
\037A)
1000 ',\
'0)
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z '.)
...)
Insulation
1.7
oJ'. :-)
Testing)
v
should be measured
between
insulated
and earth, and between conductors.)
meter
The
tester
Figure
is a high
tester
insulation
An
using a high
test voltage
in
test
- usually 500 V
is produced either by
(Figure 1.8b).
test
voltage
insulation tester
of 500
V
on
systems
board
is suitable
DC
for testing ships' equipmentrated
at 440
of
1000
V
and
5000
V
are
used
voltages
voltage (HV)
in
V AC. Test
for high
ship.)
Before applying the test, the equipment
to be
tested must be disconnected from
the
live power
supply and locked-offaccordingto standard
safety
procedures.)
To prove the basic operationof the
two probes together and rotate
the
short the
switch)
tester,
rocker
should
the
measurement
of the insulation
be made while the
resistance of a machine
machine is hot?)
an IR test
the
values. Three readingsshould
be
U-V, V-W, W-U, as shown in Figure
measuredas
at high temperatures,
more leaky (its IR
value
so testing while
hot
falls)
shows)
and
V-E
U-E,
measured
as
1.9.)
W-E.)
resistance decreases
Note: Insulation
as
temperature increases.)
An
of an IR log for a motor
example
Figure
1.10,
together
with
value
at,
IR
its
Insulation
considerably
with
changing
conditions. A single
reading
by
preventive
is shown
graphical
in
trend.)
or near, its working
resistance can vary
temperature.
indicates
becomes
00.)
and log the phase to earth
insulation
values. Three readings should be
Measure
resistance
results may
Insulation
electronic-type
on a three-phase machine,measure
insulation resistance
phase-to-phase
For
information.
ANSWER)
the
on
tester)
The pointer should indicate
and
the realistic
QUESTION)
Why
instrument).
log
electronic insulation
the 'test' button
(or press
DC.
- 'Fluke'
1.8b
Figure
inbuilt
an
(as illustrated
generator
or by an electronic
A
conductors
resistance
reading
voltage
a hand-driven
1.8a)
L\037..:..JLIJIt...J
\037'.\"
\037\037)
insulation
of the
measurement
@
@
@
resistance (IR)
one
of
the
best
to
the state of
provides
guides
health
of electrical
The
resistance
equipment.
A
.')
CD
cD
regular
Hovyever,
show
a downward
trouble
impending
maintenance.)))
atmospheric
gives
little
recording of test
trend, which
that can be remedied
Electrical Systems, Safety and
Ships'
::: i\037'!','\037')
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AC Compressor MotorNo.1
I
Comments
IR (MO)
Date
MO
40
5Jan
17
ER cold (dry-dock)
8 Mar
12
Warm
IR
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trend
,
,
,
20
19 Jun
5
Hot and
Q. ............
humid
,
,
......
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12
Sep
2
Warm,
cleaned
?
,
,
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& dried
I
I
I
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'0--------0
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I
13 Dec
25
Figure 1.10 - I R log and trend)))
Repeat test
Jan
Mar
Jun
Sep
Dec)
1.8
An
Marine Electrical
Practical
12
tester
test
facility.
measuring
It can
resistance instrument
for
(or otherwise) of
conductors.
measure the low
resistance
Routine electrical test work involves
measuring
and resistance, ie amps, volts
and
voltage
ohms.
This is most conveniently carried out using
a digital multimeter with
auto
for electronic
ranging
a
incorporates
This is a low
normally
low voltage continuity
Multimeters)
1.9
Testing)
Continuity
insulation
Knowledge)
current,
the continuity
be used to
of cables,
motor
instruments.)
transformer windings, earthing
straps,
etc. The procedure
for use is similar
to that
for the
insulation tester.)
windings,
Despite the prevalenceof digital
the focus in
./
./
correct
the
PROVE
off the
lock
and
ISOLATE
operation
of the instrument.
PROVE
./
SWITCH
./
the
to be dead.
instrument
to '0'
the
the probes
CONNECT
./
equipment
the
on
indication
Before
or 'continuity'.
that the
is essential
off, and
any capacitors discharged. The instrument
likely to be damaged.)
is otherwise
and check the
Log all readings.)
.'
In
of three-phase
case
the
is usually
more important than
the
of the readings. All readings
should
one
is significantly
reading
FLUKE 111:U\037)
motors and
transformers,the comparisonbetween
,-, rl \037.
'_I.L'\" ,)
o
I I 'Ii'I I I)
IIOUI_MAX_
readings
value
absolute
be identical.
smaller than
the
resistance
resistance
fault
value
or an open
connection
indicates
IIr)
If
others
:. 0)
OFF:
')
\\
\",
it could indicate the possibility of short-circuited
turns
or coils in that winding.
a high
Conversely,
continuity
Hz)
''---)
a high
A
circuit (eg a loose
\\
COlI VONo-ll.t::.
\037\037
Lrl.\\:o:
+,)
0\\
).)
'-)
insulation testers also
measure
resistance in the kO
of electronic
Modern
types
provide
facilities
to
and AC voltage (acV).)
range
Figure 1.12 - Digital
-
)(01)
.l'.,)
i
t
'I\"
\"0
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1.11 - Continuity
test connections)))
Me
Ii'
.;
INSULATION
TESTER UN EST
, .. let
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(
-. '.. !....
c:.: \" \037(f rrmov
:
(\342\202\254!
10 =\302\2730..
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OD O '0110)
.)
l')
Figure
multimeter)
,)
.)
is fitted
resistance
of a component,
circuit is switchedoff, locked
the
measuring
it
to the circuit.
switch
0 scale.
test
the
OPERATE
However,
will be on the use of digital
book
In all instrument
models, an internal
battery
for use when measuringresistance.)
tested.
./
this
technology,
in use.
multimeters.)
to be
equipment
are still
multimeters
analogue
j
Electrical
Ships'
be proved for correct
should
multimeter
The
operation before use. The
correct
the
PROVE
of the instrument.
operation
this,
./
procedure follows.)
a general
but
./
be carefully followed for
should
instructions
13)
resistance
To measure
manufacturer's
Safety and Maintenance
Systems,
lock off the equipment to
and
ISOLATE
be
tested.
is necessary
when using a
for a live voltage. If the
care
special
Very
check
to
multimeter
been accidentally set to the
or resistance
current
range, the instrument acts
the live supply. The
across
as a low resistance
may easily cause
local fire damage and
current
short-circuit
resulting
the meter to explode,
with
serious consequencesfor
the
probe leads are, therefore,highly
for use with a multimeter.)
recommended
together.Set selectorswitches
./
selector
all dcV
for
repeat
note the shift
of the
decimal
the
DISCONNECT
to
instrument
'dcV'
to
To
measure
./
PROVE
and
probes
switch the
OFF.)
(highest
switch positions and
point. Separate the
probetips. Set selectorswitches
to
0
(highest
voltage
instrument
correct
the
operation.
to the highest
SWITCHthe instrument
voltage
acV
or
dcV
as appropriate).
range (either
CONNECTthe probes to the terminals
being
tested. Take great care not to touch the probe
tips and rememberthat the equipment
being
./
Display should indicate zero (000)
range).
appropriate
to the
resistance range, connectthe probes
note
the
resistancevalue.
and
equipment
./
the two probe tips
connect
and
on
Switch
to the
instrument
the
SWITCH
operator.)
Fused
.
./
has
multimeter
.
PROVE the equipment to be dead.
./
./
tested
is LIVE.
NOTE
the
voltage
reading.)
voltage
range would give a more
range ).)
a lower
If
accurate reading,adjust
or 100
Display should indicate OL (over-range)
Connect
probe tips
(depending upon model).
display should indicate zero (000).)
together
.
switch positions and
selector
all 0
for
Repeat
note movement
of the
decimal
Test the
polarity
Instrument
DC voltage range also and
indication on the meter.)
battery
numeric
display.
the decimal-point
effect
be
may
To preserve
used
not
performed every time
It
been
of digital
mode automatically if
dangerous
to be
almost
proving tests are
is used.)
instrument
that these
the
However, most digital
facility.)
to the instrument
by
selector range switches while
to a live supply. However, great
not to switch into either
taken
or resistance
certainly
operate
device and
may
cause
instrument
and
danger
mode. This would
the instrument
overload
severe
damage to the
to yourself. Take time
the
to operate the selector switchesduring
what
are
think
about
and
doing.
you
operation
Fusedprobeleads(as
are
shown
in
Figure
1.12)
recommended.)
highly
the probes
DISCONNECT
instrument.)
To measure
Mostmulti
to touch conductors believing
which
is possible if they have
dead,
checked with a faulty instrument.)
is very
them
majority
for a time.)
is recommended
It
the
to standby
be
must
current
switches
selector
point.
an auto-ranging
will be caused
harm
care
./
battery life,
have
the
the
used.)
meters
the
decimal
the
operating
still connected
failure is usually indicated by the
The display may include 'BT'or
blink, or some other display
may
switch
meters
multi
note
the
No
point.)
Set selector switchesto acV (highest
range).
live supply.
Connect probes to a suitable known
Display should indicate correct voltage.)
.
to shift
off
the
current
meters
10 A maximum.
and turn
can
The
only measure current
current measuring facility
up to
is
only for small current componentsand,
circuits. The instrument
for electronic
in particular,
be
will almost
damaged if it is used to
certainly
intended
measure the current to motors and other power
circu its.)))
Electrical Knowledge)
Marine
Practical
14
current range can be extended by using
shunts
(DC) and current transformers
These
accessories
are generally purchased
(AC).
manufacturers.)
separately from the instrument
basic
The
measure
./
./
V) for
./
instrument
the
SWITCH
range (eitheracA
./
to the highest current
dcA as appropriate).
TURN OFF the powerto the circuit
and discharge all capacitors.
./
circuit
the
OPEN
measured-
to
If
often gives
measurement.
current
connect the probes in series
is to be measured.)
Turn
ON
the
current
Turn
OFF
the
over
range.)
indicates
over range in both
the diode is open-circuit faulted.
1 V in both
less than
indicates
display
the
display
the
directions, the diode may
a
short-circuit
be
faulted.)
be
The associated diode circuitry
may
be
giving false readings, so the diode must
from the circuit and retested.)
disconnected
for
the load
with
power to the circuit being
size on the meter display.)
to the circuit
all capacitors.)
the power
discharge
tested.
Note
tested
and
being
Disconnect the test probesand switch the
instrument
to OFF. Reconnect the circuit
that
was
tested.)
currents
Power
Clampmeters)
can
(AC)
a clampmeter
by
using
not
interrupted.)
The value of current
Tests)
Diode
0
1.11 Current
be measured
that
simply
a current
as
acts
transformer. The instrument'stongsareclipped
round
a single insulated conductor and the circuit
current
Often, the mostconvenientway to measure
is to use a clampmeter,which
is simply
clamped
around an insulated conductor.)
1.1
and the
connections
probe
current
which
being
If
measurement.)
current
Securely
tested
a fuse-link
for
the
REVERSE
display should indicate
directions,
ADJUST the test leadsas designated
./
be
./
current is to be
in which
removing
convenient point
in
or
a healthy silicon diode or p-n
junction.
instrument operation.
the correct
PROVE
be
should
(0.5-0.8
volt drop across the diode.
500 mV and 900 mV
between
forward
the
READ
in a
This
to
across the diode.
the two probes
CONNECT
./
The procedure to be used to measurecurrent
small current circuit is:)
it also acts as a voltmeter
the volt drop across it.)
while
junction
external
flux
around
strength
on a digital
is obtained
from the
magnetic
and is displayed
the conductor
display.)
(DC) measurement is also available
that have a flux-voltage
as a 'Hall-effect'
device.)
transducer,known
Direct
current
with
clampmeters
Many modern clampmeters are virtually
with the addition of facilities to
and currents up to
measure
and resistance
voltage
multimeters,
Electronicdiodes,and
other
semiconductor
with p-n junctions, (eg the base-emitter
a transistor)
can be tested using the following
devices
of
1 000
A.)
procedure:)
..
./
PROVE
the correct
./
SWITCH
the instrument
instrument
(\"..
. ! . .\",
\"
\"
operation.
to diode test.)
r,', --/-)
;,
II
\037D'
,.0
If the
to
the
is still
diode
circuit,
in circuit,
discharge
turn off the power
all capacitors
and
remove fuses.)
In
this
current
test
(a
the instrument
few
mA) through
is
drives a small DC
the diode/p-n)
Figure
1.13
- Current
clampmeter)))
..
\302\267
8
1 \" <AI
I
.1)
Ships' ElectricalSystems,Safety
Care
be taken when
conductors.)
must
uninsulated
power
and
in
clamp type meters can indicate
More advanced
power
AC circuits by
measuring the current
factor
in
single
additional
using
and three-phase
connections
to
QUESTION)
a 3 core cable that
around
indicator), some make a noise,others(as shown
in Figure
1.14) operate LEOs to indicate the
approximatevalue
of
It is important
voltage
that
voltage.)
is
if
carrying 100AAC to a motor?)
on
insulation
as
Zero.
damaged casing or scratched
leads should never be used
to personnel.)
dangerous
with
test
a single
around
as they
eg fuses
high
probe
voltage circuits,
must be used
(see Chapter 8).)
3-core
by the current. In a balanced
the net flux is
cable,
(or 2-core for that matter)
zero - therefore no indication.
This
is why the
connected
used
test
Great care is required
produced
clampmeter is only
conductor.)
be
can
they
the
where a special HV
is
be
equipment,
with either
Testers
ANSWER)
This is because the clampmetermonitors
the
flux around the cable, which
magnetic
not
can be dangerous if protective
and finger guards, is not fitted.)
clipped
to be
known
are
themselves
testers
Homemadetest lampsshould
indicate
a clampmeter
would
15)
PROVED to operate correctly
before
use. This
can be conveniently carried out at the electrical
workshop test panel.)
measure voltage.)
What
Maintenance
and
Electrical
General
1.13
Maintenance)
1.12
When
equipment
All
Testers)
Live-Line
is to
that supplies are
maintenance, it is important
switched OFF and locked OFF. The equipment
must then be PROVED
to be dead
to eliminate
A live-line (or voltage)
the danger of electric
shock.
Live-line
testers,
Some light
up
up to 500 V,
(eg screwdriver
are
whether
only
of various
type
with
types.
a neon)
..
.)
-.\" ...
.',--',)
-,
: .-,....\037:
.\"..\"...
.
--..\037
\037
Figure
1.14
.-. \037--,.\037\".
,.:.\"
!\",)
,....
- Live-line
-':-..;-7 \
tester)
reach
dangerous
extent.)
to be replaced. As equipmentnearsthe end of its
safe working life, its condition can deteriorateto a
be inspected for
tester is a simpledevicethat checks
or not a voltage existsat terminals.)
to wear and tear and will
the end of its useful
life and need
is subject
equipment
eventually
:.\"(-1.
\".\":
.\037:
.:::-'..-;:--)
C-..ck .)
The purpose
extend
the
of maintenance,therefore,is to
useful
life
by
repair
of defective parts and to maintain
serviceable
condition.)
The marine
environment
and/or replacement
it in a safe and
is particularly
electrical equipment due to
the
damp,
arduous
salt-laden)))
for
Practical Marine
16
Electrical
of temperature and constant
extremes
atmosphere,
Knowledge)
is in
particular
The continuous operationof equipment
on
vibration.
Shipboard
of correct
maintenance.)
equipment
and optimum
ship demands high efficiency
economy to help keep operationalcoststo
and described proceduresthat
work to be done to
need
the actual
failure.)
specify
equipment
prevent
Planned maintenance is carried out at fixed regular
intervals, whether the equipmentneeds it or not.
The aim is to prevent breakdownand
this
type of
maintenance
has the following
advantages:)
board
a
minimum.)
.
electrical engineer (or chief engineer if
there
is no electrical engineer on board) must
get
to know the ship's power system and
its equipment.
The ship's technical library
must
be kept in order
and be updated to the actual condition
of onboard
Electrical services and equipment
applications.
must
be kept
under continuous
observation so that
normal
conditions become known
healthy
operating
and
abnormal
becomes quickly apparent.
operation
An efficient
Faults should be pinpointed
and
before
corrected
Breakdown
.
planned
as:)
.
occurs.
breakdown
is repairedor replacedand
are
other
specified
procedure carried out.)
maintenance
There
any
several
disadvantages
to breakdown
maintenance:)
X
serious
A
of equipment
breakdown
may
cause enough downtime
to put the ship out of
commission until it is repaired
X
several
if
occur
breakdowns
simultaneously,
the available manpower, skillsof the crew or
knowledge in the field of the breakdown may
not be sufficient
to cope
adequately,
resulting
in
X
more
Planned
further
is when
maintained
carry
delays.)
maintenance
equipment
according
more
(preventive
because
favourable
times
at
can be ordered in
equipment
replacement
is maintained in a safe
equipment
with reduced possible dangers
condition
.
services
manufacturer's
a specialist
are
advance)
short-life
components
scheduled
intervals.)
Condition
are replaced at
(preventive
monitoring
maintenance)
This is when equipment
is regularly
monitored
and tested. When
indicates
that a
monitoring
breakdown is imminent,
the
is repaired
equipment
or replaced and any other specified
maintenance
are carried out. Regular insulation
procedures
and vibration
testing
testing are two forms of
condition
Condition
regular
monitoring.)
monitoring is also carriedout
intervals. The aim is to forestall
by predicting
probable failure from
results.)
the
at
fixed
breakdown
trend
shown
by the monitoring
is not
equipment
type
of maintenance
subjected
maintenance.)
Equipment is regularly
according
are taken
and
condition
to a monitoring
schedule.
is
to unnecessary
monitored
Measurements
of insulation resistance, temperature
vibration
Contacts and other parts
(of motors).
subject
to
is regularly inspected and
to a manufacturer's
timetable)
ship
utilisation
labour
effective
out at times favourable
at convenient
required, these can be obtained
times to suit the ship operation
for repair can be ordered
spare
parts
required
that
maintenance)
This
operation
The advantage of this
delays
some items of equipmentmay need
the
services of the manufacturer
to
specialist
out repairs, which are expensive and may
cause
of the
where
(corrective
is left untouched
until
a
At this time, the equipment
the
.
.
maintenance)
This is when equipment
is carried
maintenance
in
maintenance
and reduced downtime
of operating efficiency
levels
advance
monitoring.)
Breakdown
higher
maintenance
is carried out
to the ship's staff
maintenance
maintenance
\302\267condition
.
.
Maintenancecan be classified
breakdowns
to
a
breakdown occurs.)
.
.
Fewer
produces
deterioration
are
inspected.)))
Ships' Electrical Systems, Safety
All
are recorded
findings
record file.
trend of
historical
an
in
is carriedout
No maintenance
until
the
test results indicatesthat it has become necessary.
or
The equipment is then either replaced,
repaired
on a
as specified
overhaul,
subjected to a major
job card.)
Knowledgeand
records
is required. The
system
recordedmeasurementsof insulation
a falling
may show
resistance
a progressive
should
equipment
trend,
indicating
The
degradation of insulation.
be inspected and repaired beforethe insulation
falls to a dangerously low value.)
resistance
from
live
of typical
list
letters of the mnemonicFACERAP
key steps to logical fault
finding:)
seven
A
of a motor may follow a rising
indicating
occurs.
Immediate
the name and classification
(fault)
a fault
of
deterioration. Bearings should
failure
before
are
electrical
vibration
be replaced
to
to experience
FACERAP
The
of the
The recordedmeasurements
trend,
suggested
should be updated
according
show the most probablefaults.)
F
bearing
including
and faults for a particular
remedies. These lists
symptoms
plus
equipment
from
a safe distance
equipment can be monitored
using an infrared detector or camera.)
progressive
essential,
Fault charts
the
Hot spot temperatures emitted
are
experience
knowledge of components,methods and systems
with their operational characteristics.)
together
A
A maintenance
17)
knowledge
(underpinning)
Background
Maintenance
and
the description of the fault
or its related symptom
(appearance)
the operationalreasonfor
C (cause)
repair
the
not
but
or maintenance is probably
necessary
should be put in hand at the earliest convenient
E
fault
the consequentialeffect
(effect)
the
of
fault
moment.)
R
the correct personto take
(responsibility)
action
remedial
Fault
1.14
Generally, fault
A
Finding)
finding
adopted
to
is not
a good understandingof the
of
the
operation
particular equipment and a general
into
some
of the diagnostic skills used to
insight
solvethe problem.)
Planning
what
The
has a well-plannedstrategy.
is carefully considered before deciding
fault-finder
evidence
P
an easy task and it
action
to take.)
A good diagnostician will
strategy
A
approach
six-step
should
Collect evidence (stop and
2.
Analyse
evidence
3. Locatefault
Memory
.
logical thinking
.
perception
.
spatial/mechanicalability
.
persistence.)
the
(inspect
fault.
be utilised:)
1.
think).
(check assumptions).
and
test).
4.
Determine and remove cause.)
5.
Rectify
fault.
6.
Check
system.)))
use:)
.
of the
repetition
Search
rectify
the procedureto avoid
(prevention)
to have
is essential
A good
the standard procedure
(action)
fault
Two
Chapter
Distribution)
Electrical
2.1 Power Distribution
extends from both
sections by means
electrical distribution
of a ship's
function
The
system
to
power
safely convey the generated electrical
item of consumer equipment connectedto it.
every
is the main
The most obvious element in the system
of
which
for the neutral
connection
earthed
The
System)
busbar
main switchboard
the size
of power
conductors,
upon the power output.)
of the
ends
depends
is to
ie the ship's main switchboard.
distribution
centre,
bulk power to motor
The main board supplies
of the main board),
part
group starter boards (often
boards.
section boards and distribution
Protection,
placed
eg circuit breakers and fuses strategically
the system, automatically disconnects
throughout
a faulty circuit within the network. Transformers
and low voltage
interconnect the high voltage
of the
sections
distribution
system.)
is
The operational state of a distribution
system
constantly monitored by the power management
system for active and reactive load sharing,
and frequency
current
(power factor is also
voltage,
often
Protection
monitored).
monitor
appliances
over
and
for over and undervoltage, overcurrent,
faults.)
under frequency, reverse power and earth
The
services are broadly
electrical
required
consideredas main
and
supplies.)
emergency
large electrical loads have
of
at high voltages (HV)
operating
generators
11 kV. Such high
even
3.3 kV, 6.6 kV and
voltages
with
Ships
are
very
necessary
economically
to reduce
in
the size of current,
power
high
systems
so reduce
and
and equipment
the size of conductors
required.
more
such
is becoming
at
high
voltages
Operating
increase.
common as ship size and complexity
oil and gas production platforms
Offshore
operate
at up to 13.8 kV, where
equipment
weight saving
at these
is important. Distribution
high
systems
their
neutral
points earthed
voltages usually have
or earthing transformer to the
a resistor
through
of an AC power system
hull.
The
ship's
frequency
can be50
or
Hz
Hz.
60
the world, the national
In
and
Europe
is 50
frequency
of
Hz, but
most
it is 60 Hz in North
America
and in a few other
countries. The most common powerfrequency
for use on board ships and offshore
adopted
is 60 Hz. This higher frequency means
platforms
run at higher speeds,
that
motors
and generators
reduction
a consequent
with
in
size
for a given
power rating.)
Main
A
ship's
supply
distribution
electrical
scheme
generally
follows shore practice.This allows normal
equipment to be used on board ship after
'marinised',
of a sea
rigours
380 V (440
it must
(eg
in
The majority
380 V, 50
system.
have a three-phase AC,
of ships
Hz (440 V, 60 Hz) insulated neutral
that the neutral point of a
This means
star-connectedgenerator'sstator
earthed
a 380
to the ship's hull.
V, three-phase
For
ships
is not
winding
built
in
Europe,
system is common.)
AC 380 V, 50 Hz earthed
Three-phase
In
on board.
neutral systems can also be found
this type of system, the generator's neutral
point
to the neutral busbar in the main
is connected
to the
switchboard
which, in turn, is connected
Note:
ship's hull.)
low power single-phase supplies
lower
voltage of 220 V, which
from power step-down transformers
to the
their
windings,
primary
connected,with
the
withstand the
ozone,
vibration,
humidity,
high temperature,
seawater, etc that are likely to be encountered
of the ship).)
various
parts
life
operate at the
is derived
being
to withstand
where necessary,
and
Lighting
industrial
V) system.)
the main
The electrical energy is routed
through
switchboard, then distributed via cables to section
to the final
and distribution
boards, and ultimately
load consumers.)
are the means of
and switches
flow of electric current. The fuses
the
the distribution system from
protect
The circuit
breakers
interrupting
the
and
relays
effects
damaging
Figure
2.1 shows
distribution
or
branching,
of large fault
an HV/LV
system.
system
The
currents.)
layout
system
and
it
has
of a ship's
is called a radial,
a simple and
logical structure. Each item of load is supplied at
size of cable and is
its rated voltage via the correct
protectedby the correctly rated protection device.)))
20
The
and
Electrical
Marine
Practical
main electrical
non-essential
Knowledge)
load is divided into
services.)
essential
boards.
necessary for loads requiredto
dangerous
has its own preference
generator
%
is low set, generally at 110
instantaneous
operation.)
which
with
current
a potentially
handle
each
addition,
overload trip,
are
supplies
Emergency
In
generator
its own circuit
Essential services are for the safety of personnel
and for the safe navigation
and
of
propulsion
the ship and they
be supplied
may
directly from
the main switchboard
or via section boards or
distribution
150 01b with
has its own overcurrent relay to trip
set at
breaker, which is typically
high
a 20 second delay.)
Each
If
services
non-essential
To maintain
generator
a preferential
load
operation
shedding
during
arrangement
.
.
overload develops, the preference
sets
an alarm and acts to trip selected
trip
relay
non-essential
loads. This reduces the generator
load
so that
it may continue to supplyessential
trip
- air
2nd
ventilation, galley
container sockets on boarda
cargo
order
of tripping varies with the ship type.
When sufficient non-essential load has been)
The
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0
0
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2.1 - HV/LV power system)
plant
seconds.)
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- 5 seconds
services
or
0
0
0
conditioning,
- reefer
trip
0
DE1
disconnects
order
a defined
containervessel refrigerated
board a reefer carrier- 10
load.)
its nominal
1st
and laundry
If a generator
maintaining
in
develops, the
(PMS)
time intervals, eg:)
an overload,
is
current
employed. This is achievedby an analogue
monitoring relay, called a preferencetrip relay.)
circuits,
condition
overload
a generator
powermanagementsystem
situation.)
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3 x 440V 60 Hz ESB)
't.)))
M)
on
Electrical
the
disconnected,
overload
preference
resets
trip
own
its
with
can
also
frequency
monitoring
relay in the
event
of under-frequency
(eg due to
decreasing
speed
of the generator's prime mover).)
initiated
In
the
by
the
is incorporated
electronicrelay
(or
based PMS) that
the
undervoltage, overcurrent
and
To maintain either the preference relay
trip or the
PMS-initiated safety trips' settings as originally
specified,
they must be periodically checked when
the registersurvey
Emergency
supply
An
electrical
emergency
out.)
is carried
also
should
batteries
be installed
(such
as GMDSS).)
On passenger ships, SalAS Chapter
requires
Part
11-1,
D,
power supply
primary
emergency
a diesel-driven
for up to
generator
the
that
is provided by
36 hours (18 hours for non-passenger
In
vessels).
an emergency transitional battery
must
addition,
also be installed to maintain vital
services
(mainly
a minimum
of
lighting) for a short period typically
3 hours. This emergency battery
is to ensure
that a
total blackout cannot occur in the transitional
period
between loss of main
and the connection
of
power
the emergencygenerator.)
must be
service
power
Another set of
equipment
logic controlover and
generator
reverse
power.)
programmable
monitors
also
(hydraulic
the alarm system,
locally to supply automation,
navigation aids and the ship's communication
the preferencetrip
into a combined
of cases,
majority
protection
be
generator is usually installed,
battery large enough to sustain
starting attempts or to air start
start) supply.)
starting
consequent
several
The generatorpreference
trip
system
21)
a diesel-driven
so
load is disconnected.)
no further
and
Distribution
in the event
of a main
failure.
This
power
is for emergency lighting,
alarms,
communications,
doors and other services necessaryto
watertight
maintain
and permit safe evacuation of the
safety
provided
ship.)
require
Regulations
that the
not
contained.
An
have an
mover and
fuel supply tank, starting equipment
its
own
engine
and switchboardin the
The emergency
operate
as
as prime
vicinity.)
supply should automatically
quickly
45 seconds
near
as possible
after the failure
but
later
not
than
of the
main
source
power. Emergencybatteries should
be
arranged
of
are switched into service
immediately
a main power failure.
Emergency
can be hand cranked, but are usually
so that they
following
generators
started by compressed
air or a
battery to ensure immediate run-up
following
a main power failure. Other cranking options
be provided
to ensure safety, eg cranking
should
means
of
the
electric
starter driven with a set
by
a hydraulically
driven starter
of batteries or with
a
hand-driven
accompanied by
pump and hydraulic
automatically
accumulator.)
Although
may
regulations
the solesourceof emergency
suitable battery
may
be
permit
in
2.2.)
Figure
There is no standard electrical
supply
arrangement
as all ships differ in some
Both the main
respect.
the
by
main service generators during
normal
operating
In the
conditions.
event
of an emergency, only
the
services
are supplied by the
emergency
generator.)
emergency
in practice
very large and)
The emergency power system must
be
and available at all times and this level
ready
a
of
care and maintenance.
The system
must
be tested
at regular intervals to
confirm
that it does operate correctly. The testing is
carried
out during the weekly emergency
normally
fire
and
boat drill practice sessions. The main
are not shut down, but the emergency
generators
sources
are energised and connected to
power
the
services for the period of the
supply
emergency
reliability
requires
practice
session.)
The emergency
special
generator may
main power supplyduring
or in
mode
parallel
with
Independenceof the
other auxiliariesof the
ensured.)
one
and
in
the
Classification
be
time
lay
as the
used
(either
in
single
of main generators).
power supply
emergency
main engine
plant must
The regulationsgoverning
the
in
are
detailed
SOlAS,
power
a battery to be
power,
physically
incorporating
system,
must
generator
emergency
combustion
internal
have
upon any other engine room
A battery, when fully charged,
is self-
dependent
supply.
power
distribution
typical
emergency power supplies, is shown
and the emergencyconsumersaresupplied
emergency power
source is a generator,batteriesor both. The
emergency
power source must be self-contained
and
A
emergency
national
Societies'
from
be
source
regulations
rules.)))
of
22 PracticalMarine
Electrical
Knowledge)
MSB 3 x 440v, 60Hz
ESB
3 x 440, 60Hz)
III
III)
.
QE1
,
1
1 1
QE2
1
QE4,
QE3,
I
MSB
- ESB
Transfer
line
TE2
TE1
Emergency
consumers
3 x 440, 60Hz
QE6
QE5
3
1
1
60Hz
x 220v,
III
Rectifier
220vAC/24vDC
11
8\037
Emergency
consumers
3 x 220v, 60Hz
EG
24vDC
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!
3 x 440V, 60Hz
! !
400kVA
Emergency
consumers
24v DC)
Figure
2.2 - Emergency
2.2
Insulated
power supplies)
and Earthed
Neutral Systems)
An insulated system is one that
insulated from earth (ship's hull).)
An
earthed
connected
has
system
to earth.)
main
Shipboard
(ship's
is totally
the supply neutral
electrically
point
insulated
earthed
although
hull),
to limit
transformer
impedance
3-
Single-phase A C
insulated
fault
D
Three-phase AC
..L
--)
neutral
L)
insulated
neutral
L1)
G)
Load)
N)
G
L2
3-)
L3
+
3 x phase
load)
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J:)
Single-phase
AC
Three-phase
earthed neutral)
earthed neutral)
2.3 - Insulated
earth
load
L3
N
Figure
systems
3 x phase
L2
G
Load
--
neutral
L1
G
and earthed neutral
systems)))
and
earth
from
can also be encountered.Similar
ashore
systems
are normally earthed to the ground. HV systems
(;2:1000 V) are usually earthed to the ship's hull via
a neutral
a high
earthing resistor (NER) or through
L
..L
at 380 V AC
LV systems
440 V AC are normally
AC
current.)
Distribution
Electrical
The priority
electrical
of the
continuity
essential equipmentin the
fault
ship is to
board
on
requirement
maintain
event
of electrical
parts
supply to
of a single earth
conductor
earthing
occurring.)
equipment must be earthed.The
connects
the metal enclosure
to earth (the ship's hull)
a dangerous
to
.
of two parts:)
consists
voltage
current
carries
which
Conductor,
the current insidethe
which keeps
insulation,
A
A motor
10
circuit
basic
in
Figure
2.4(b):)
.
An
open-circuit
fault
as at A,
conductor,
.
faults
occur
can
that
are shown
is due to a break in the
current cannot flow
so that
to a break in the insulation,
is due
an earth fault
the
hull
as at B, allowing the conductorto touch
or an earthed metal enclosure
a
short-circuit
in
the
is due to a doublebreak
as at C, allowing both
If:)
an
(b)
an earth fault,
and
(c)
a short-circuit
fault)
open-circuit
what
occurred,
of fault current
will
that
in the
occur
(a)
the open-circuitfault
depends
circuit
under
fault
(b)
electrical
of earth faults occur within
due to an insulation failure or a loose
equipment
which
allows
a live conductor to come into
wire,
with its earthed
metal enclosure.)
contact
fire
against
earth
the
that
enclosures
in each
may result from earth faults,
and other non-current carrying
the
has
infinite
V
220
==
==
ZERO
000)
fault has NO effect
on the circuit
so I remains
at 10 A (because this
is an insulated system)
(c)
short-circuit
by the 0.0
the
only
Isc
V
==
==
Z
of electric shock
the dangers
V
Z
majority
and
flow
so:
I ==
current,
protect
current would
ANSWER
on
conditions.)
To
circuit
case?)
impedance,
the overall impedanceleft
The
fault
(a)
load.)
size
have a total
fault
insulation,
conductors to be connectedso that a very
large current by-passes, or short-circuits,the
The
from a 220 V insulated
operates
The supply cables
of 0.01 O.
system.
impedance
.
always
QUESTION)
conductor.)
Three
it
the
through
circu it
.
that
ensures
volts.)
at zero
remains
it from attaining
to earth. Such
prevent
with respect
earth bonding of equipment
A circuit
V
220
0.01 0
fault impedance
is limited
10 of the cables, so:
==
22 ')000
A
or
22 kA
metal
metal)
C
-
A)
.)
t
G)
II.
/
Conductor
.
Insulation
I
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Load)
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(
Earth)
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Figure
2.4 - Circuit
faults)
23)
Earth)
(b))))
Marine Electrical
Practical
24
2.3
distribution
to a short-circuit
the
through
current
fault
fault occurs
earth
a single
If
protective
an
of an
line
in
system
for most marine
across
the generator
hull.
The
ship's
resulting large earth
would
cause the line's
immediately
device
or
circuit
(fuse
breaker) to trip out
fault
more effective
is, therefore,
system
earthed
services, which
electrical
is why
systems.)
High voltage
systems (3.3 kV
ship are normally
earthed
the generator neutrals
of
it is used
continuity
maintaining
and
on board
above)
a resistor connecting
as shown in
earth,
via
to
2.6.)
Figure
faulty
be
would
cause arcing damage at the
a single earth
By contrast,
location.)
fault
fault
will not
and the system
as shown in
system
2.5.)
Figure
This is the important
to operate
not
on
'A' occurring
one line of an insulated distribution
cause any protective trip to operate
would continue to function
normally,
point:
continues
equipment
earth
a single
with
provide
fault as
it
earth fault at 'B' occurred on another
line
in the insulated
system, the two earth faults
would
be equivalent to a short-circuit fault
together
a second
the
(via
would
hull) and
ship's
protection
operate
disconnection of,
a risk
creating
An
insulated
two
earth
earth
to
the resulting large current
devices
and cause
perhaps,
the
safety
distribution
L1)
G)
services,
current. Such a neutral
usually assembled from
of such an earthed HV
is usually
earth fault
full load
generator
the
resistor
earthing
metallic
system
will
connection
wire. This is monitored
current
cause
resistor
maximum
earth fault
(E/F) relay to create alarm
(NER)
to flow
and
neutral
earth fault
trip functions.)
in the
an
by
Regulations
insist
distribution
systems.
danger from
earth
hull within
hazardous
explosionof the
zones, which may cause an
flammable
cargo.)
An exception allowed by regulating
where a tanker has a 3.3 kV earthed
a system is permitted
that
providing
fault)
G)
bodies
system.
forward
of the
the
hazardous
area.)
into
Fuses)
occurs
Such
the earthed
extend
Electrical supplies forward
of the
bulkhead are usually
three-phase
L1)
Earth
Loads)
engine room
engine
room
440
V insulated)
Earth
fault)
Loads)
B
L2)
L2)
/)))
Earth fault path)
2.5 - Double
earth faults
in an
insulated
in
that tankers have only insulated
This is intended to reduce
fault currents
circulating in the
Earth fault)
Figure
is
The use
plates.
means
that a single
Certain essential loads (eg steeringgear)
can
be supplied
via a transformer, with its secondary
to maintain
of supply
winding unearthed
security
the
event
of a single earth fault.)
bulkheadand
therefore, requires
lines to cause an
Fuses)
value of each earthing
chosen so as to limit the
current to not more than
system does not
of the ship.)
system,
on two different
current
to flow.)
faults
fault
essential
The ohmic
does
a complete circuit so no earth fault
will flow.)
current
If
insulated
than
be equivalent
circuit. The faulted electricalequipment
isolated from the supply
immediately
and
so rendered
safe. However, the loss of
could create a hazardous situation,
power
supply
if the equipment
was classed essential,
particularly
eg steeringgear.The large fault current could also
the
An
supply to essential
on the live
it would
system,
Faults)
Earth
of
Significance
earthed
Knowledge)
system)
Distribution
Electrical
G2
G1
3-)
Earthing
I
3 -)
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switch
Earthing
Gen VCB
resistor)
25)
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L
)
6.6 kV 60 Hz HV
3 x
Earth
fault)
MSB)
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Earth fault path)
2.6 - Neutral
Figure
and obtained from
3.3 kV/440
a three-phase
Their
V
to the main
the
to
indicate
switchboards
and
emergency
isolated
section
earth
fault
on
each
of
an
presence
V
the
440
and
220 V
on
of a distribution
system,
eg
sections. An earth fault monitor can be either a
or an instrument (or both) to
set of indicator
lamps
IR value to earth.)
show
the system
An earth fault
indication
Earth
in a three-phase AC system
2.7. When the
in Figure
lamps
are arrangedas shown
(no
system is healthy
with
equal
brilliance.
(as
illustrated
the lamps glow
fault occurs
in the line 3 earth fault
faults),
an
If
earth
2.7), the lamp connected to
dim or is extinguished(in the case
in Figure
example
that
earth
half
on one line
be fitted
should
monitor
line
goes
of a short-circuit to the earth). The other lamps
so will glow
an
increased
voltage
experience
brighter
than
is that
disadvantage
major
very sensitive and will not
earth
of a high impedance
transformer.)
step-down
power
in HV system)
earthing
before.)
the
development
instruments.)
fault. This has led to
use of earth fault indicator
and
One common type of earth fault
a small DC voltage to the distribution
resulting
resistance
current
mA for earth
60
the meter indicatesinsulation
kO or MO.The monitor
triggers
an
This type of arrangement
to meet regulations that
has
value.)
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Earthlamp
L2
Earthlamp
L3
Earth fault
lamps)
Earth lamp
L1
Earth fault
test push-button)
l
EF monitoring example Earth fault on Line 3)))
Figure
2.7 - Earth
fault
monitoring
with lamps)
when
developed
circuits
in
hazardous zones must
be
through
the system insulation
monitoring
continuously
alarms are given
and
resistance. Visual
audible
resistance
falls below a pre-set
if the
insulation
passing
L2)
E---
that
Earthlamp
Test)
in
directly
alarm
been
demand
L1)
monitoring
lamps), and
resistance
is reached.)
value
set
Any
insulation
system.
the
limits the maximum
to only 1 mA
instrument
earth fault monitoring
(compared with about
connects
monitor
DC current is a measure of
of the system.)
The injection-type
or
have been the most
indication
Earth
lamps
common method used for many years and are an
is easy to understand.)
that
inexpensive installation
are not
the presence
they
indicate
its
Marine Electrical
Practical
26
Knowledge)
QUESTION)
What
the
would be the ohmic value
earth
fault current to the full
2 MW,
2,000,000
I L ==
load
AC generator?)
pf, 3.3 kV, three-phase
0.8
NER to limit
of a
rating
an
of
ANSWER)
UnderE/F
V
A
437
voltage of:)
a phase
conditions,
= 1905 V drives
=
pH
==
13 x 3,300 x 0.8)
the
fault current)
3,J},0
P == -V3 x VL x IL X coscp
system:
VL is line voltage
(3.3 kV),
IL is the line current and coscpis the power
factor.)
a three-phase
In
where
The
An
at
generator
full
HV system
the
current
load
11 kV) is usually earthed
-
(1 kV
is:)
point via an NER. This
the
neutral
(and therefore the
to be monitored for alarm/trip by
neutral
generator
arrangementallows
earth fault)
current
a current
transformer
1905
V
437
A)
==
So its ohmic value has to
NER.
the
through
4.4
Q
of the earth fault
system can be provided
Measurement
earthed
ways and one method
is shown
current
in a
in an
number
(CT) and E/F relay.)
'\\ L2
()
I
Power load
network)
L3)
I)
380V .
fau')
sulalion
Earth fault)
local alarm
+
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uz
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Figure
External alarm)
Q1)
L1
CI
of
2.10.)
in Figure
3x 380V - supply)
G
3-
be:)
2.8 - Earth
+ I
\037
----\\---\\
I
Current R I
limiter
busbars.
.,-)
Magnetic
is arranged
a special three-phase earthing
to the HV system
This high impedance earthing transformer
to limit
the
maximum
permitted
an
alarm/trip
voltage
connected protection
action
core)
1
'\037
.=\037
............'..l..\037) CT
EF relay)
by DC injection)
monitoring
is connected
current and initiate
Trip
---------9
I)
Alternatively,
transformer
--m
starter)
m
(\037)
fault
Motor
External
alarm
relay.)
E/F
signal to a
Figure 2.10 - Corebalance CT)
the current
transformer (CT) measures
Here,
the phasor sum of the three line currents supplied
If the motor
to the motor.
is healthy (no earth
the
sum of the currents measured
phasor
faults),
by
G1
the
CT
is zero.)
3-)
N)
If an
earth
fault (E/F) occurs in the motor, an E/F
current flows and the phasor sum of the currents
is
no longer zero. The current
monitored
by the E/F
relay is used to trip the contactor in the starter to
isolate the faulty
motor
circuit.)
GCB)
The earth
_
\" I
III)
)
three-phase
busbars)
circuit)
monitor
earth
on the
switchboard
shows
fault on the distribution
It is up to the maintenancestaff
to trace
of the fault and then
for) the exact location
to clear it as quickly as possible.)))
system.
(search
Figure 2.9 - NER
fault
the presence of an
Electrical Distribution
of earth
method
The
described
EF monitor &
alarm system)
IT])
circuit,
the
earth
If
MSB
fully
as
shown
busbars
earth
an
M
Q1
Figure
circuit-breakers F1, F2,
miniature
fault,
the earth
ci rcu it.
until
fa u Ited
Q11 Q12 Q13 Q14 Q15)
Q\\ttt
\037)
this
If
breaker
fuse
board
11111)
Consumers
A
- Earth
would
method
simple
loads
feeding
in the distribution
breakers
shown
in a distribution
monitors
fault
system)
be to open the circuit
etc (as
011,012,013,
system
in
2.11),
Figure
the
earth
fault monitor
one at a time, and watch
while observing which circuit breaker, when
opened, clearsthe earth fault. The earth fault must
circuit.)
then
be on that
particular
circuits cannot
In practice,
in this
disconnected
for lighting
this
be randomly
way. Some vital
DFB,
is the
No.1 (CCT1) is removed to
fuse-pair
supply to the load (Figure
tester
The
IR
lead
to earth
outgoing
If
(IR > 1 MO),
healthy
and
is now connected
(megger)
connect the test lead to
circuit
Fuse-pair2
(CCT2)
'b'
in a
at 'a' and
is
now
an
If
faulted
the
then
and tested
removed
similar manner.
All
are
fuse-pairs
fault
earth
circuit has
checked
in
turn
to confirm
healthy or faulted.)
whether
L2
L3)
DFB)
DFB
50Hz
III
l
llli
L2)
1
EF monitor &
a b
system
CCT1
CCT2
CCT3
I
T1
0
T2)
3
!
! !)
Tm3
\"
'
,.'1-',\\111;;1\",,1,/.
\037_
:\037KO
J; UHnUT'\037 I ,
--,
....
1'-.\".
p!!
'.)
I
4)
2
\037
CCT3
\037
(
Q3
Q1
'a'
the test. If both 'a' and 'b' are healthy,
1 is healthy
and fuse-pair 1 can be replaced.)
repeat
been located.)
be interrupted, such as causing the main
to stop, possibly in dangerous
narrow
waters.
Therefore, tracing the earth fault must be
with the operational requirements of
coordinated
the
electrical
services.)
ship's
alarm
one
with
(hull) and the other lead to 'b' (the
terminal as shown), and a test applied.
service
may
3 x 380v,
IR tester
faulty
2.13).)
the
isolate
is indicated (IR = low)
engili8s
MSB
circuits,
an
monitor,
lighting circuit.)
At
2.11
F2, which supplies a
(DFB)
must be used to determinewhich
3 x 380 I 50 Hz)
Figure
indicates
is no earth fault
as there
closed in
the earth
and
opened
monitor
fault
is circuit
distribution
then,
distribution
2.12.)
F3 and F4 are sequentially
turn
lighting
example
fault monitor on the 220 V lighting
board (DB) indicates the presence of
distribution
3 x 380 I 50 Hz)
in
will be
clearance
fault
an
for
27)
I
,- .)
\037
.)
Lighting DB
3 x 220v,50Hz)
Q41
Q21
III)
11111
Figure
F11 F21F31
F41
Consumers
Figure
2.12
-
Three-phase
F51)
220v)
to single-phase distribution)
2.13
- TR
testing at distribution
testing IR at the faulted
should be removed, all switches
When
and all lamps taken out,
as
fuse
the
circuit,
shown
board)
should
fuses
be opened
in Figure
2.14.)))
28
Electrical
Marine
Practical
Knowledge)
Lt)
lamps
removed)
Switch
open)
--E:3o 0)
CCT2)
--E:3o 0)
CCT2)
\037
\037)
Breakers)
lamp 1
lamp 2)
\037
CJ
Detailsof main
and main
--E:3o 0)
(0
--E:3o 0)
/0)
oSl)
')
\037;\"D)
- IR test on a
2.14
Figure
breaks the circuit
conductor
sections.)
At
the
then
function of any circuit breaker (CB) is to safely
onto and break open the prospectiveshortcircuit
fault current
expected at that point in the
circuit. The main
contacts
must
open rapidly while
to special
the resulting arc is transferred
arcing
Arc chutes
with
contacts above the main
contacts.
it
arc splitters quickly
stretch
and cool the arc until
The CB is open when the arc is quenched.)
snaps.
Feeder
several
conductorsconnectedto 'a' and
isolated
switch
the
Close
IR is low then
are usually
or miniature
(MCCB)
MCCBs
Theseare
clear and
'b' are
circuits
distribution
protected by moulded-case
(MCB) circuit breakers.)
distribution
board, test at 'a' and
supply
at 'b'. If both
have
an IR > 1 MO then the
healthy.
for main generators
breakers
3.)
are included in Chapter
circuit)
lighting
into
circuits
make
and
This
circuit
feeder
The
r)
i]:la;.,i/.,
j\037
.\037
.
\"'1/ :, '.'\\,
'
. :. .
liD
-('001....
I'
\037 =r- '!.. ST' 8
II
\"
.,;\037 j\037\037'1g
EF clear cdr)
C -
Circuit
Distribution
2.4)
Fuses
removed)
and re-test at 'a'. If the
lies
on the conductors
the earth fault
moulded
current
fitted in a
air circuit
breakers
case. They have a lower normal
and
main
breakers
(50-1500
A) than
compact
plastic
rating
a lower breaking capacity(see Figure
2.15).)
beyond the switch.)
1, remove the fitting
lamp
the conductors
as shown to
down the circuit. Use the IR
At
and
disconnect
further
break
tester
on
each
'\
of
\037.:..)
these disconnected leads. If one conductor
is
indicated as having
an earth
fault (suppose
it is
the conductor
between lamp 1 and lamp
then
2)
the earth fault
lies
at lamp 1 or lamp 2 or on the
SChl1eider
\037 Electric)
ttDY/5OHz
\037)
;.\037 \037E.\"
\302\2530
'42
42
500 '30
525 '22
\037:
,\"\" ,to
10 ,:)
conductor.)
\037 :)
'
'
IEN
60947-2
IEC
.---\037--- ,
- ....
NElIA
All!HIC
(I<A):
iiiN---:::.S----40av - 42
: \037_.._\037\037)
fittings
lamp
to trace
A lamp
Dampness
is damaged
must
insulation
\037)
.,.,....
J.'t.\"'.)
and then some precaution must be taken
the future ingress of moisture.)
prevent
that
or weakened by
again. If surface
cleaning
\037
\037..,
:.r\037\037:::T:\037\037
','
,,\037.,.,\037.
-.10' : J'1r)
j- A....\037
..I\
,,\\
::)
\037.
must be replaced.
be dried out by
heat
Insulation
. :J .....)
.)
PIOO)Jj)Z\037
that
in
f))
Qf:>')
\037
examination.)
fitting
': '\"7)
, ;)
When located, the damaged insulation
must
be
The
method
of
the
earth
fault
repaired.
repairing
on its cause and this is determinedby
depends
visual
\037H':)
SiiieOtt.
must now be opened and visually
the exact location of the earth
inspected
fault. The method of tracing
the
earth
fault is that
of continually
down
the
circuit
into
smaller
breaking
and smaller
sections until it is finally located.)
Both
MMtUVR
01. .0(\"04)
has
been mechanically
overheating
dirt
will usually
must
to
damaged
be made
cause, a thorough
cure the fault.)
is the
gentle
good
Figure
2.15
- MCCB)
They usually have an adjustablethermal
overcurrent
and an adjustable or fixed
setting
overcurrent
trip for short-circuit protection
magnetic
built
into
the case. An undervoltage trip coil may
also be included within
the
case.)))
Electrical
Operation to close is usually
lever,
but
by
a hand-operated
closing gear can
spring
are reliable,
trouble free
motor-charged
also be fitted. MCCBs
and requirenegligiblemaintenance.If the
operates
ON
the
in
be tripped
should
the mechanism
be
should
breaker
for long periods,
position
and closed
a few
and cleanthe contacts.Terminals
for tightness or overheating
MCBs must be replaced if faults
checked
MCCBs (around 1000 A
be removed for inspection and
under
a short-circuit
tripping
cleaning.Following
the
breaker
should be inspected for damage,
fault,
and its insulation
checked for correct operation
resistance measured. A test result of at least 5 MO
The front
of larger
cover
can
rating)
is usually
usually
other
Any
required.
can be used for
ship, from
generator
breakers.
The
demand that
every
distribution
capacity may
be fitted for very high
breaking
fuses
backup
fault levels.)
short-circuit
prospective
to small
breakers
limited
MCBs
These are very
air circuit
small
breakers
fitted
plastic cases (see Figure 2.16). They
current
ratings of 5-100 A and generally
in
moulded
have
thermal overcurrent
and magneticshort-circuit)
Electrical
board
on
generation
AC, 440 V,
three-phase
fixed lighting
and
ship is typically
380 V, 50
units. Ships with
HV
6600/440V units
(see
at
Hz (or
60
Hz),
loads
V AC single-phase
from
low power
other
are suppliedwith 220
0
very efficient (typically>90/0) static
the
on board
application
Transformers)
2.5
while
operation
faulty
or overhaul by
replacement
requires
usually
manufacturer.)
MCCBs
- no
develop
maintenance is possible.)
will develop.)
damage
capacity.)
to free
times
transformer
require
generation
three-
room
phase transformers to supplythe LV engine
and accommodation
sub-switchboards, eg using
Figure
2.17).)
The principle of operation
of a single-phase
transformer is straightforward.
An applied
AC
to
the
sets
voltage (V1 )
primary winding
up an
in
flux
the
laminated
steel
alternating magnetic
core.)
have
The flux
an
induces
emf
in
the
whose
secondary,
size is fixed by the ratio of primary
and secondary
turns in the pair of phase windings (N1 and N 2 )
to give:)
I
\"
\"(
(-
\"' ,:')
:))
&1 MERLINGERIN
G
The
,ulti9
C60N ___
\037 _
N1
V2
N2
secondary
current
11 13
I I
82
230/400 V
L6ciQO
\0371
It
\037.,
2
23756)
i (4
through
is the
sets
the
current
V2 is available
voltage
a load.)
to drive
load connected
to the secondary that
size and power factor angle of the load
12. This is matchedon the primary
side
from:)
\037
12
V 2)
'1)
l)
t'
,.1
,
\"', \"\\, L
\037 'C
Transformers
kVA)
(,
(,
I)
1)
',,\037)
Figure
2.16
- MCB)
29)
protection.
They have a very limited
breaking
used in
capacity
(about 3000 A) and are commonly
final
distribution
boards
instead of fuses. The DB
is supplied
via a fuse or MCCB with
the
required
breaking
it
Distribution
units.)))
are
rated
in
apparent
power
(VA or
Marine Electrical Knowledge)
Practical
30
ANSWER)
QUESTION)
A 440/220
V
load of 5 kW
transformer
single-phase
at
0.8
supplies
factor load.)
power
a
From:P2 = V 2 X '2 X COSqJ, '2 =
Calculate
secondary
and primary currents
5000
(ignoring
transformer
power
losses).)
220 x 0.8
/1
=
/2 X
== 28.41
-
==
P1
V
X 1
1
2
2 A
14
X
cosqJ)
1
-@0-)
-co-)
T1
o
.)
380 I 220
1000VA)
380 I 24
500 VA)
D
Primary winding
T2
--
If
-i-.
I I
I,
j
/'
T3)
-,
\037
,'\\, I
;-----1
I
/
.r -\037'I-
-/-'_0
Secondary
I)
!
,--
e
o
:JC)
-';
4-----.
,
:JC
=
440.
or, check from
X COS<p)
A)
-V2 = 28.41x 220
\037
p2
V
b
/()
winding
.;:)
.$)
, rr,cr,c,'{
,t. t '.., t,
. ,F'(.\037..\"
(. \"
,
,-')
r t', C r
r \"'l\037t-'t!\037')
r)
-)
Single-phase
transformer)
Three-phase transformer)
o)
1-)
-.)
14' f)
:i O'' ,' \037
-.
r
I
..-
\"'-\"'-
\037\\
\037)
\037
\037
. . , . ...\"..\"..)
I
J A
,
-..
1
::\037 eu::=
\"\"'6:
. t.IJ'\":.sAf
...fWt:
I.,aAX
,..
......,
....
_....1..... .....-:JCIIiI1I)
it
\037\"\037
i , .)
,,
\".
'(,
0)
.. '42G380
Single-phase
Figure
2.17
- Transformer
.
---,;,-)
.)
transformer)
arrangements)))
'\
G)
;,.)
\037)
Three-phase
transformer)
\302\267)
Electrical Distribution
are generally air cooled and
steel enclosures
that
are
switchboard.
adjacent to the main
etc). In the
they may be fitted
be
transformers
The
located
often
Alternatively,
so that
are
Three-phase 440/220V lighting transformers
units
usually composed of 3 separate single-phase
to form a three-phase
interconnected
arrangement.
This enables easy replacement
of a single-phase
a fault. The alternative is to use a
unit if it develops
ratio
voltage of 400/-v3
V. An
configuration
(other
either
links or power
configurations, such as delta-starand
are
also
in
using
use)
copper
example
of the
is shown
in
are
earth
fault
occurring
circuit.)
are static
like
items of equipmentthat
reliable and trouble free. However,
very
usually
all electrical
equipment, transformers must
usual maintenance checks.)
to the
subject
be
An
delta-delta transformer arrangement
2.18.)
Figure
== 230
a neutral earthed
such
Transformers
star-delta,
conductorsbetweenthe phasewindings.
a secondary
gives
a line-neutral
phase
system will immediately
the protective fuse or circuit
breaker.
This
operate
of supply leads to rapid identification
of
interruption
on
the faulty
circuit
and
standby unit.)
V
eg a 6600/400
line voltage of 400 V plus
supply,
only.)
a delta-delta
it will
ashore
systems
delta-starto provide
The power transformers for use on three-phase
insulated systems are generallyinterconnected
in
failure,
breakers
unit's
circuit
on three-phase HV/LV
are generally connected
a three-phase,
4-wire LV
for use
earthed
on a common magneticcore.This type has to be
completely isolated in the event of a fault on one
phase
by the
taken
be
Transformers
mounted
with all windings
unit
three-phase
single
of the working
from the circuit by
(eg emergency
system,
detection
smoke
event
isolated
the load will
are not required.)
enclosures
transformer
switchboard
the
within
aids,
navigation
lighting,
consumers
essential
in supplying
in sheet
mounted
31)
At
specified
regular
switchedoff,
covers
intervals,
transformers
removed
and
all
must be
accumulated
and deposits removed by a vacuum
cleaner
and suitable brushes. Windings
must
be inspected
for any signs of damage or overheating.
Winding
resistance
values are measured, recorded
continuity
and
with each other for balance. Any
compared
dust
If
a fault
on one phase of
develops
the faulty
arrangement,
unit
can
an
such
be disconnected
(via the links)creating an open-deltaor 'V'
connection
and a three-phase
supply will still
available,
although at a reduced powercapacity.
This
is a useful safeguard.)
be
differences
faults,
in continuity
readings will indicate
winding
such as short-circuitedturns. The insulation
of all windings
resistance
Twotransformers from the main
as well as two transformers from
switchboard,
both
the
windings.
emergency
are usually provided to supply the
switchboard,
V
in such a way that
one
220
consumers
ship's
is generally strong enough to bear
the
other
unit to remain in
while allowing
standby.
This
particular
All
ensures safety)
arrangement
ESB 3 x 440, 60Hz)
MSB 3 x 440v, 60Hz)
respect
The
reading
connections
full load
transformer
with
III
test
must
be investigated and rectified.
Cable
be checked for tightness.)
must
observations
and
results
recordedfor
Busbars
should then be
reference.)
future
3 x 440 160Hz)
III)
ttl
Q07 '\\ QosJ
QE1
Q06
1
\037
Q09
su
-QS
>
\037
\037T2
MSB 3 x 220v, 60Hz
1
1
-T1
\037TE2
QE6
QE5
1
ESB 3 x 220, 60Hz
1
III
3x440 /3 x 220;
65kVA; Nl::J.
1u 312 5 L3
\037
-Q9 \037f}j- -I
I> I> >
tL_)
1u 312 5 L3
\037
-Q1 0 \037f}j- --
2 T1 4 12 6 13)
2 T1 4 12 6 13)
Emergency Consumers 220 v)
Busbars 3 x 220 160Hz)))
2.18
- Power
transformers
su
-T2)
3x440 /3 x 220;
65kVA; Nl::J.
11)
11)
Consumers 220 v)
ttl--
\037f}jI
I> I> I>
tL_)
TE1
Q10
1
--Q7 Hft
I
>
I>
tL_)
QE4,
QE3,
1)
T1
Figure
must be measured,
to earth and to the other phase
cause
of any low insulation
resistance
connection)
I
I> I>
tL_)
>
Marine Electrical
Practical
32
Transformers are usedto supply
\"'\\\"\"1
\\\"\\
0.8 1.0
,,\\'\\'\\\037
:$'0,6
\037.......
:2\"\"0.4)
\"kW \\\\\\'\\\"\"i'\"'I
600 800
V
,'\\'\\\\'\\
.....,.,
400
.::\037.......
f--200)
-(-!.Slw
\",\\\"'{\"I
400 500
,,\\'\\'\\\\
(-ul(/]_
voltages,
mains
circuit
The
associated
VT
on a 380 V
220
V.)
The
ratio specified
and
output
1 A.
3 x 380V,50Hz)
will
will be
and
its scale
have
marked '380 V/220 V
on a CT similarly
currents,
eg
150/1
its input
details
A CT is used on a
steps the current down to
instrument will have its scale
'0-150 A' and will be marked '150/1 ACT
and
circuit
The associated
calibrated
( \",)
\037)
instrument
ratio'.)
ratio'
Main LV busbars
and
its input
is used
steps the voltage down to
and
'0-380 V'
calibrated
A
\037.......
\037200)
\037,)
\037
output
150 mains
/'300
-
:'U1W_ \"E-\037)
on a VT details
eg 380 V/220 V
specified
and
instruments
small
currents
protection
relays with proportionally
and voltages derived from the large currents
and
in
a
network
voltages
high power
(see Figure 2.19).)
kA
ratio
The
Transformers)
Instrument
2.6
Knowledge)
.)
of instrument transformers does not
to operators.
The 220 V output
danger
use
The
eliminate
a VT will
from
a severe,
apply
possibly
lethal,
shock to unsuspectingfingers!)
CT1
1000/5A)
F1
The
1A)
opened
mains
while
VT1
Excessive
primary
will develop
heating
380/110V)
of a CT must never be
load current is flowing.
circuit
secondary
in
an
open
circuited
terminal
must
high voltage arising at the
terminals.
If an ammeter
is to be
the CT secondary
circuit,
output
be first short-circuited, with the
primary
circuit
switched
CT, with
an
extremely
open secondary
removed from
Wattmeter has
current and voltage inputs)
2.19
Figure
- Instrument
connections
connected to earth.)
with
CT
and
are commonly
transformers
(VTs) supply voltmeters and
the voltage-operatedcoilsof instruments
and
A
standard
of
220
V is
relays.
secondary voltage
used. Current transformers (CTs)supply
ammeters
and the current-operated
coils of instruments and
use
The
the
transformer, the lamp
transformer
is similar
in
to a VT.)
function
of VTs and CTs allowsstandardised
and
to be used.
relays
improve
safety
by providing
current
isolated
supplies
and protection
not
of
5 A or 1 A.)
a standardised
instruments
VTs
lamp fixtures on switchboards
transformer
type, with a
small
transformer
built into the lamp fitting.
The
transformer
a 6 V or 12 V output. The
provides
with a small bayonet
lamp is of low wattage
not an accurate
instrument
cap fitting. Although
indicator
Miniature
VT)
Voltage
relayswith
off. The secondary short-
the CT when the primary
damage
current
is switched
on. For further
one
safety,
end of the secondary winding
of a CT or VT is
not
will
circuit
They also
for monitoring instruments
,, \\....)
used at voltages
primary
less than
or bar
3 kV.
-i-)
are
\037)
CTs
primary type.)
The bar primary
CT is used with
type
very
high
current
primary
ratings and the wound primary
type
is used for small step-down ratios, eg 1000/5
A bar
50/5 A wound primary.)
primary;
Current
transformer for motor starters
with a ratio 100/1A
(shown
w!th opened
terminals
Figure
\037J
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f;
;
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I
:i t. '. \037
!
\037
tIJ\037\037,,;
en \037\037)
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\037C
100/1 A)
are built like small power transformers.They
normally
k)
CT1
relays.)
can be of the wound
E)
L1)
low voltage and low
2 20 - Bar primary
CT)))
access coverto
).)
sequence
the
of
the phase
supply is 'correct'?)
to know whether
it essential
is
Why
shore
incoming
ANSWER)
as the ship's supply
Shore
2.7
A
shore
Connection)
so that
is required
sequence
A reversed)
(red-yellow-blue).
Supply
supply
same
is the
it
for major
down
is
remedied
motors
magnetic
results.)
any two
by interchanging
conductors of the shore supply
connection box.)
a
produce
three-phase
at the
cable
are disconnected
from the
generators
will
this
cause
a
brief
mains
blackout
(as
ship's mains
before
is applied).)
power
ship's
and their prime movers can be shut
overhaul during
a dry docking
generators
all
in
because the direction of their rotating
fields will be reversed,
with disastrous
shore
the
(red-blue-yellow)will
shaft rotation
reversed
This fault
that
mean
'correct'we
By
sequence
phase
QUESTION)
33)
Distribution
Electrical
shows a typical
shore
connection
but some variations occur.)
Figure 2.21
arrangement,
period.)
There must be a suitableconnection
box
located
to
the
shore
accept
conveniently
supply
cable.The connectionboxis often located at
to the accommodationor in the
and/or
\302\267A
the entrance
cable,
supply
terminals
suitable
have
must
room. The connection box
to accept the shore
generator
emergency
to
The connection box must
or an isolator switch
and
a circuit breaker
to protect the
box to the main
have
fuses
cable linking
the
connection
switchboard,
with
a data
plate giving
details
and
ship's electrical system (voltage
and showing the method for connecting
supply cable.)
A
a phase-sequence
indicate
shore supply
and
voltmeter
are fitted to
correctsupply
phase
lamps
an
integrated
generally
cause
and
overheat.
cause motors to
voltage is generally not
may cause motors to run slower
\" --..1
'
---.:..
. .---.....
\037---_
'\"r
.--\037)
, \037)
\037;e
5.; .)
am)
\\..- -)
a rotary
,=\" ..:.)
i'\".-)
\037)
(.)
pointer
three-phase
motor.)
,
main
, .I
I.:..\037
' .
f
'j .1
\037\037-..:..
\", \037
. 1'\"
:)
;:\"..
therefore, be disconnectedbeforethe shore
can be connected to the main
switchboard.)
'r
! \037)
'.. . -
aI.;i. \037,.\".
.;. - -'1
l\"\037\037:
.=..)
.
I _<, L
I'::;';:
I
\037)
it
breaker.
In general,
connecting switch or circuit
is impossible
to parallel the shore supplywith the
The ship's generators must,
ship's
generators.
\037i.)
-,; li)
. ..-:;...{
.)
f
.)
'-,
\037
-)
- \037
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-' . .\037-----.)
I.
.
\037
\037)
supply
:.j)
:\037)
--.)
switchboard
shore switch on the main
circuit
interlocked with the generator's
so that it cannot be closed until the)
j \",)
\037-, ,)
the
Normally,
is electrically
breakers,
:,:\\ ')
.' .)
.: ..'
Figure
2.21 a - Ship's shore connection
and
serious
but
and overheat,
so
or to stall.)
an indicator is provided
switchboard,
a lamp)
to indicate that
the
shore
(usually
supply
is available for connection to the busbars
via a
the
rapidly
loads
a lower
.)
1
At
more
accelerate
this may overstress the driven
equipment
It will also
\037)
or
small
will
voltage
higher
indicator (PSI)
voltage and
indicator may incorporate either
for 'right' (R-S- T) and 'wrong'(R-T-S)
monitoring
overheat
to take excess current
frequency)
the shore
sequence.)
phase-sequence
driven by
\302\267 a
to run
motors
cause
will
of the
A phase-sequence
two
frequency
higher
faster, be overloadedand
an earthing terminal to
the shore
earth.)
including
earth the ship's hull
supply may have a different
frequency
of the ship's
voltage to that
system.)
shore
The
board)))
Marine Electrical Knowledge)
Practical
34
.
-
-+
')
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2.21 b - Shore-based
Figure
connection
board)
1 PS01 - PHASE SEQUENCE INDICATOR)
15001
OA03
P501
\037
\037
\037\0370
2)
HE01
20003)
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r
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Panel1
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E
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0
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X
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X
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u.
Panel2
Fromshore supply
Figure
<\302\273\037
L1
L2
=
r=:r-
C\\I
E
E
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<\302\273
X
.....
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u
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N C\\I
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u.
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9
10
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E
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C\\I
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MainSwitchboard.
Panel6,1,ACB10002)
2.21 c - Ship/shore connectionboard)
ANSWER)
QUESTION)
If your
for 60 Hz at
ship is designed
what value should the shore supply
at 50 Hz?)
operating
440
voltage
to
about
Supply voltage should be reduced
V be
if
380
V.)))
Distribution
Electrical
If
shore
the
frequency differs from the ship's
then, ideally,the shore supply
supply
normal
frequency
voltage
should
differ
same
the
in
proportion.)
means
that each vessel brought
in future should be fitted
with
a facility
This
Power Supply (AMP)
of pollution
and sustained environmental
The
risks
damage in ports allover the world are becoming an
Maritime
increasingissue.Over the last
attention has been focusedon
from the auxiliary
pollution
frequent,
and
terminals
around
their
auxiliary
engines
a continued
to ensure
increasing
reducing
the
of ships
increasing numbers, the ports
the world. These ships keep
running when moored in port
in ever
that
15 years,
diesel
engines
power supplyfor
power from shore and back while
port.)
Finland,
Many port and ship operators in Denmark,
Norway, Sweden, the UK, the USA, etc use shorewhile
in port.)
basedelectricity
moored
:\\
.)
essential
'\\)
be given to the measures that
t
connection
shore
.
N TAl
\037
capabilities
.
'-
iIo.
\037--t.:O\\
\\\\,'J.
,
A)
\037
....\037\037\\
\037-
I .-...,
GHA')
'
Q2- VOTEC
...\". .- \037.-.
.-,; -', \037
\037
I
_
\"
-
be taken
should
of
the
combustion
to reduce the contribution
marine
marine fuels other than
gas oil makes
to acidification. Amongst other measures, it
recommends
,\", -
f
to
consideration
requires
--\037:.)
4
Parliament has adopted a directive,
which
2005/33EC,
IIt:-.J)
Q')
in
n)
ports.)
also
a
US State of California
adopted
resolution to take preventive measures, called
measure
for auxiliary
toxic
control
'Airborne
The
diesel engines on ocean-goingvesselsat berth
Port' (93118.3, Title 17, Chapter 1,
a California
in
subchapter7.5,
the
lill1iting
by
of Regulations).
Code
California
calls for
This section,
in emissions
a reduction
time during
engines
are operated
docked
at berth
which
on regulatedvesselswhile
a California
in
Committee
port.)
Protection
agreed
(MEPC)
in
of
VI
with
to a
inserted
were
to deal
'MARPOL'
2011
July
number of new regulationsthat
Annex
diesel
auxiliary
IMO's Marine Environment
The
the
into
called the International
In addition,
(IEEC).
on or
date
new
all
st
ships
2013
July
Certificate
with a keel laying
will also
be required
Energy Efficiency Design Index (EEDI)
Efficiency Management Plan
Ship Energy
the
meet
the
and
after 1
Energy Efficiency
2.22
Figure
- AMP - shore based)
alternatives
to this system are available.The
mount the cable management system on
the
is made
ship or shore. The connection to shore
to an integrated
technical
via special HV cables
fitted
into the quay. This application occupies
pit
of space
and consists of the following
a minimum
electrical
connectors
components:
(up to 12 kV),
a
an optical fibre
flexible
cables,
slip ring assembly,
a
cable
drum and an
a
motor
accumulator,
reducer,
A few
is to
first
electrical control
panel.)
greenhouse
emitted from ships. The measures will affect
gases
all ships and require the issue of a new certificate
to
at the
moored
,)
European
EU
that allows
of the ship's
with
power plant
over the
power supply substation for taking
services.)
The
service
into
brief parallel working
a shore
Alternative
, ',.
,.'-,)
.-<
.
\" ,
--'.
\
t'
>
'.
,
,T, \037\"t<\037:.
'r; .)
J
- --'
,,-
I \037'
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I
. \037
:'1\", .\037,,:...
' .,'\037
1\"
,. \"
l)
/ \"\\\\
,
'-,)
.\037.
(,/''''''''
,___,----)
'.-
\\
\037..
o. .)
'I \\.)
,I,..
\037
'\\.
/.
',,')
\\:: .,..
,Ii \037'\037..
<',
(SEEMP).)
j)
\037
\037_:) 'Iii
\
\037)
In
35)
with
accordance
\"In
some
ports
for
some
ships,
these
shore power may be available
but this is generally aimedat
in the pori area. If the shore
air quality
improving
there
based power source is carbon efficient,
may
consider
be a net efficiency benefit. Ships may
using
onshore
power
if
available.\
\
...
new regulations,)
\037\037)
...... '..J.\037'
....)
Figure
2.23
- AMP -
ship
based)))
Marine Electrical Knowledge)
Practical
36
is to
alternative
Another
a standard-size
inside
fitted
However, the rules regardingship to shore power
increasingly strict in some ports in
have a similar system
container, which
are becoming
can be placed on the ship.As the whole system
is inside a container, and thereforecompletely
it can remain in a fixed position
on board
modular,
for longer periodsor, if necessary,
can be moved
on board another ship.)
Such systems
part of many ports'
becoming
movable
power network (barge
the
--\"\"'i
\" \"
. .,
(
.. -
-)
..'
\"
,
-.
.. , '
.
'.'.
+
\037
\037
\" \")
-
-\" --
'1
.-
\037
:\037', CAN'
l
\"'.r
\037-::--.P
--
..
..- \037\037
';r
l\\\\
I
....
\\..' ,:rfJ'
\\
\"J.
\"0- -...
',:\".\037r. -
\037\037\037
-:!3\037
'., .\\,.\\
.' \302\267
\037
'\"':\"--;__ ..:
c; 1 '
III \037
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.
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J
CS'2 . f' \037\037
_
\037 _
1)
. \037\037._J.-.
-........::)
.
hl
hJ1
,..to
,
1
\\
-\037
distribution
unbalancedloading,
in
most
protection
limit
power protection
protection
- AMP -
No matter
barge mounted)
is
with generator
included
is
in
an
discrimination. (Reverse
3.))
Chapter
how well designed and operated, there
of faults developing on
possibility
the
always
electricalequipment.Faults
Overcurrent
protective relay
relays monitor current and/or
our examination
to overcurrent
of protective
appreciation
\037.)
2.24
system
power
and undervoltage protection, together with
=-=--)
- \"'-\"\"\"':I:\037.\037)
.)
\037:.
\037 .--)
reverse
etc. The HV
lists typical
2.25
Figure
overcurrent,
overtemperature,
(for generators),
power
shown
over/under
frequency, earth leakage,
over/under
voltage,
Protection
a fault occurs.
when
system
relays are usedto monitor
voltage, we will
\037,':\":'.'\037)
Figure
that
available
As
.'.,...)
.:\037\".':
Protection)
.. --)
-::.)
\037.-)
80\302\260/0).)
functions.)
If, 1)
ARINe\
\037
,--')
- 0-1
-C;:--'.
., .\".:)
.'
'II
j;...
?' ,:,\"
...,,\037.
\\
-:-----\037.)
'
.
..._ .,or;; -:::::s - \037..
.\037
by 2020
many forms of electrical protection
are designed to protect the
are
There
.)
\037I .
\037
.1
.-#- .... ....\037
be 70\302\260/0and
Circuit
mounted or vehicle-based).)
*.. ...---....------.-......-.-.....-
power
it must
2.8
\037' .,.)
shore
without
may not berth (by 2015,
used by ships
must
be electrical;
capabilities
2017
by
vessels
from 2015,
where,
of
50\302\260/0
are
and
stationary
California
connection
can
due)
develop
(Inst.)
Overcurrent (I/t)
DE1
DE2)
DE3)
DE4)
Undervoltage
Unbalanced
load
\037
3-
Reverse power
Earth
\037
)
1
*
1
Overcurrent
2
3-
-\037
--
leakage)
1
1)
(Inst.)
Overcurrent (lIt)
3 x 6.6 kV 60 Hz HV MSB)
.,)1
.,
*)
*)
/)
\037)
\037\037
*,
1
I)
)
1
Overcurrent (Inst )
*m)
Undervoltage
Unbalanced
Earth
load
M)
(lIt)
Earth leakage
Overtemperature)
Overcurrent
(Inst.)
(Inst.)
Thermal overload
Undervoltage
---.J)
- HV
AE)
6.J...)
Overfreq
uency
U nderfrequency)
2.25
Overcurrent
leakage)
Overcurrent
Figure
I
3x 440 V 60 Hz LVMSB)
protection scheme)
Lockedrotor
Earth
cp
.,\037)
L)))
leakage)
Electrical
to natural
and
wear
incorrect
tear,
operation,
accidental damage or neglect.)
essential
of
equipment
endanger the ship, but probably
hazard is fire. Overcurrent
(FR
and equipment
effect) in cables
and
overheating
possibly
of conductor
equipment
is such that,
heat
the
flowing,
A copper
cause
will
can
rated
full load current
does not raise the
withstand
cannot withstand
compounds)
in excess of 100\302\260C. At higher
.
insulation
its
burnt
or
temperatures
temperatures,
suffers irreversible chemical
changes,loses
properties
and
Short-circuit
out.
and
overload
currents must, therefore, be detectedand rapidly
cleared
before damage occurs. (See Section 1.5.))
protection
fuses, contactors,
relays.
of circuit breakers,
consists
scheme
and
overcurrent
undervoltage
A circuit breaker, fuse or contactorinterrupts
current. An overcurrent relay detects the
the trip action.)
current
and initiates
fault
the
fault
in order
to maintain
isolate
faulty
remaining
healthy
equipment
the power supplyto
circuits
in
the
the
system
to prevent damage to equipment
from
the
thermal
and magnetic forces that occur
short-circuit
and overload faults
during
.
high
and
disconnect
To
35\302\260Crise
very
electrical
ANSWER)
and
80\302\260C(ie
an
heating
(melts at 1083\302\260C), but
organic materials such as cotton
the insulation
The
system.)
protection
why
in
to
from electric
personnel
protect
shock.)
its insulation
(generally
becomes
distribution
of 45\302\260C).)
conductor
temperatures
plastic
much
equipment
three reasons
is essential
.
with
about
an ambient
above
resistive
fire.)
developed
temperaturebeyond
may
most serious
used in cables
size
The
the
37)
QUESTION)
Suggest
The breakdown
Distribution
The circuit
safely
and
must be capable of
breaker
or fuse
rapidly
interrupting
current.They
be
must
a short-circuit
mechanically
strong enough
to withstand the thermal
and
fault
current.
produced
of
the
breaking
current
the
by
breaker
circuit
forces
magnetic
The size (strength)
or fuse is specifiedby its
which is the maximum
fault
capacity,
it can safely
interrupt.)
an MCCB may be continuously
rated
a rated current of 600 A. Its breaking
it can
capacity may be 12.5 MVA, which means
a
fault
A
current
of
16,400
safely interrupt
(from
12.5 x 10 6 /-v3 x 440 == 16,400
A).)
For
example,
at 440 V with
=1
I
I
c=J
\037
G
.
t
Short-circuit
cr-.I
fault
location
:J
Generator
Transformer
Main
Switchboard)
Figure
2.26
- Short-circuit
fault
location)))
Lighting
distribution
DFB
Lamp
Marine Electrical Knowledge)
Practical
38
Short-circuit
0.025 Q
--J
I
G
0---..
\037
/'
0.01
Q
I
fault
location
0---..
If
I
0---..
..
0
0.015
Q
I
I
{]
Load
DB
Main
Generator
Switchboard)
- Fault
2.27
Figure
circuit)
fault current level at a point
in
prospective
a circuit is the current that
arises
due to a short-
The
circuit at that
The size of this
is
determined by the total impedance
of generators,
cables and transformersin the circuit between
the generator and the fault (see Figure 2.27). This
total impedance is generallyvery small,
so the
maximum
A
as
current
(called
be very
large.)
fault
can
current)
the prospective
V, 5 kW, 0.8 pf three-phase
440
shown
in Figure
2.27.)
load
power
The normal
full
p == -v3 x VL x IL X cos<p
So, the
load full
fault
load is supplied
440 V
is:
0
Note
that the
fault
fault
occurs
J3x
the
generator.)
it is
to
is)
5,000
VL xcos<p)
the nearer
increases
less, the circuit breaker (or fuse) is liable
and cause fire.)
explode
If
of a protection system to disconnect
the
faulted
circuits and to maintain
the
only
electrical
to
circuits
is
supplies
healthy
The
I L ==
fault
A)
17,600
level
to the
the
switchboard,
fitted.)
(W))
P
==
0.025
is:)
level
A
12,571
at the main
For a short-circuit
level
at the DB,the fault
The circuit breakeror fuse must have a breaking
current capacity in excess
of the prospective
fault
current
level expected
at the point at which
it is
is)
current
load
==
(0.025 + 0.01) 0
fault current
short-circuit
V
440
2.26).)
Figure
(see
point
for a short-circuit
and,
==
8.2
A
ability
called
J3x440xO.8)
discrimination.)
protective
a short-circuit fault
terminals.)
Suppose
at the
occurs
load
is achieved
Discrimination
coordinating
by
the
ratings and time settings of the fuses and
overcurrent relays used betweenthe generatorand
current
The total
is:)
impedance
the
ZF
and the
+ 0.01
== 0.025
V
=
ZF
the
prospective
8,800
A)
== 0.05
prospective short-circuit fault
IF
So,
+ 0.015
=
440 V
0.05 0
current
0)
is:)
= 8,800 A)
fault current
as shown
load,
If
a short-circuit
2.28.
Figure
fault occurs
Figure 2.28, the fault
level at the load is
in
The
protective
devices nearest the load have the lowest current
rating and the shortest operatingtime.Those
nearestthe generator
have
the highest current
and
the
rating
longest
operating time.)
operate
the fault.
all
protection
current
devices
the
in
lampholder
will be large enough
in
from the
to
generators to
the 5 A fuse protecting the lamp
the lo\037est current rating
and
shortest
time
in
the
so
it
will
be
the
operating
system,
to
will
This
action
clear
the
fault
quickest
operate.
and leave all other healthy
circuits
still connected.)))
circuit
has
However,
Electrical Distribution
150 A
15 s)
500 A
20 s
39)
60A
15A
10s)
5A
Short-circuit
5s)
Inst.)
fault
location)
\037
I
1
J)
G1
1
0-.
3-)
I
I
I
I
\037)
I
I
G2
I
____I)
3-)
Figure
In
the
2.28
- Protective
case
of fuses,
discrimination scheme)
it
is generally
that
accepted
if consecutive
discrimination will be achieved
have a ratio of about 2:1. The
shipbuilder
the current ratings of fuses, togetherwith
and time settings of relays, in the
current
fuses
specifies
the
protection
scheme.)
It
is
important
to
maintained
that the original settings are
correct discrimination.)
achieve
to a
The general term 'overcurrent'
applies
full
load
current
increase
overthe
small
relatively
of
due
to
mechanical
overloading
(FLC) rating (eg
rather
a motor),
caused
Generally,
to
match
Short-circuit faults in LV distribution
Main
supply
Overcurrent
MCCBs
fuses,
feeders
short-circuitsby circuit
magnetic trip
OCIT
inverse
(overcurrent
to operateat a definite
minimum
time, which is
This
is
called
an OCIDMT
design.
type
inverse
and
definite
minimum
(overcurrent
time)
OCIDMT
can
also be combined
relay action.
with
an instantaneous
(high set) trip to give the
fixed by
the
current
fastest
caused
action against extremelyhigh
by a short-circuit fault.)
currents
increase
(.)
<D
CI)
....)
circuits
and cleared almost
are mainly detected
by
an inverse current time
time), ie the biggerthe current,the faster it will
operate
(see Figure 2.29). The basic inverse 1ft
tend towards zero time for the highest
curve
would
T
o
make
the relay action more precise
currents.
at very high fault currents, the action is arranged
a CT, is
an overcurrent, supplied from
time
with
an
a
delay
appropriate
by
relay
the protected
circuit.)
instantaneously
have
called
fault.)
a short-circuit
by
detected
massive
the
than
types
relay
characteristic
The
Protection
Overcurrent
All
and MCBs.)
are usually
protected against
breakers
with instantaneous
action.)
Definite minimum
relay
.
Magnetic
.
thermal)
.
electronic.)
types:)
time)
o)
Ir
I Amp)
1m)
(High set)
instantaneous
Minimum
Figure
2.29 - Inverse current/time
operating
(I/t)
current)
curve)))
Practical Marine Electrical Knowledge)
40
2.30,
relay, as shown in Figure
directly
converts the current into an electromagnetic
force
to operate a trip switch.
One type is the attracted
armature
action
similar
in construction
to a simple
but
with
an
signalling
relay,
adjustment for the
current
The
time
of
operation is fixed at a
setting.
definite minimum time, which is usually
less
than
0.2 seconds. This is regarded as instantaneous,
ie
with no deliberate
time delay.)
A magnetic
A
can also
trip arrangement
currents.
(differential)
with a single phasing
effective
bell-crank
mechanical
operate
unbalanced
with
This is particularly
motor fault.
In this
further
bend
two of the bimetal
case,
strips
with increased
direction
normal
the
in
line current, while the other cools down
allowing
strip to move relatively backwards (differential
this
.)
action)
to cause
time taken to heat the bimetal
strip
sufficient bending fixes the requiredtime to
the relay can only be achieved
trip. Resetting
after the strip has cooled down back to the
ambient
The inverse 1ft overcurrent
temperature.
for
of a thermal relay is very
useful
characteristic
Its
the indirect temperature protection of motors.
far too long for
thermal
time delay is, however,
The
knob)
Adjusting
'))
,),\"\\\"',,\\
\302\267\037
__i
Contacts)
'*
..
\037, ,.,.,'
t
I,..)
--,)
c)
I)
a short-circuit fault so instantaneous
protection
must also be used in the form of fuses or a circuit
,...)
,.)
\037\\
'II)
. .'
, . ,..'
t\037l\037
*)
.
breaker.)
).
Trip drop flag)
C;)
.....
)
\\)
coil
Operating
\\
armature)
Attracted
Figure 2.30 - Magnetic overcurrent
relay
(instantaneous
action))
To obtain a magneticinversetime action,
motor overload protection, an induction
is similar
but the disc movement is
so is not allowed to actually
is very small, but
A
armature element and
The
rotate.
relay,
disc travel
a set of trip
and time settings are
an attracted
including
disc
induction
element,
will
action (high set current) and
instantaneous
measured current
a proportional
into
supply.)
auxiliary
by
to operate
sufficient
adjustable. combined
an
constrained a spring
Both current
contacts.
give
for
employed. This construction
energy meter used in a house
a kWh
to
switch
eg
disc
is usually
movement
relay usually converts the
voltage. This
the
is then compared
with a set voltage level within
or
which
be
unit,
monitoring
digital
analogue.
may
In an analogue
in Figure 2.32) the
unit
shown
(as
time
is obtained
delay
by the time taken to charge
This
a
up
capacitor.
type of relay has separate
and time settings,
for
overcurrent
adjustments
with
an
instantaneous
The
electronic
trip.
together
within
a
DC
the
low
amplifiers
voltage
relay require
V
24
V
DC
derived
from
a
220
AC
power supply, eg
overcurrent
An electronic
an inverse/time characteristic.)
Here, the input
from
(CT) is rectified
to
is
a line
produce
current transformer
a DC voltage that
to the line current. This voltage
C2 at a rate set in conjunction
capacitor
proportional
charges
determines
the
R5, which
potentiometer
inverse time characteristic for the relay. When
with
exceeds the predetermined
the
detector
circuit drives power
(set
by R2),
transistor
T1 to operate
the output
electromagnetic
RLA, which switches trip and alarm contacts
relay
this
voltage
capacitor
level
Figure 2.31 shows a thermal
bending action of a bimetallic
are
the
utilises
strip (one per each
a set of incorporated contacts,
phase) to operate
which
that
relay
in turn
intended
to trip
a contactor
in
the
circuits.)
external
or
circuit breaker.)
An instantaneous
current
applying the output
to the input of the
Full
load
the coil,
(FLC) will flow through
each phase of the load. This
wired in series
coil
heats
trip
lever.)
with
up the bimetallic strip, which is used as a
by
R4.
Both
event of overload, the current
heat radiated by the coil rises.
In the
and
the bimetallic
mechanism
strip
and
This causes
triggering the trip
NC contact opens.)
to bend,
the
increases
the
the
inverse-time
and
magnetic
designed give
to
(typically
of the
Therefore,
current,
less
a short-circuit
is obtained
by
bridge rectifier directly
amplifier with a voltage set
for higher values of fault
operation
trip
an
than
fault.)))
delay circuit is bypassed.)
electronic relays can be
instantaneous
trip
almost
0.05 seconds
or 50 ms) to clear
Distribution
Electrical
41)
Current input bar
,
Bimetal
circuit
Trip
Radiated
heat
, ,
Heater
vl
.!.
----
Contact
f\\
-
strip)
-)
,.....
Current
Bimetal
Load
Heater
input)
strip
terminal
()
\037
2T1)
Indirectly heated)
Heating element)
Current
setting dial)
test knob)
Trip
I
I
I)
Front cover)
Current input bar)
, !)
TEST
-)
..
,)
LRD2:
IS 17
\\
*)
Hand/auto
0.'
---;\037
\037)
\037
button)
Stop
reset setting)
\\\\
12r<:18
1
Reset button)
----)
n. P
-r
*)
91(
-__
(
98
95
\037\\!
2T\037
----)
c:.
Aux. contacts terminals)
96)
Load output
\
4 T2)
terminals)
6T3')
\0379\037971
-F1
12-18A
(In = 14A))
\037
T elemecanique
\037981)
thermal overloadrelay
LRD
and relative diagram's symbol)
Figure
2.31
- Bimetallic
thermal relay
action)
in MCCBs
relays are commonly fitted
overcurrent
MCBs to give a 'longtime'thermal
trip in addition to a magnetic action for an
instantaneous
trip with a short-circuit fault.)
Thermal
and
is where
a calibrated test current
the
normal
load
circuit.
This
through
requires
a large current injection test set. The
test
set is a
Primary
transformer and controller,
ie it gives
Overcurrent
circuits
relays
protection
in
are generally driven by
power
transformers
large
current
The CT secondary usually
for full load current in its
overcurrent
calibrated
current trip
a low
rather
voltage - high
like
current
a welding
set,
output.)
Small secondary
injection currents (5-50A) are
current directly into the overcurrent
relay,
fed
(CTs).)
All
injection
is fed
relays
test
levels
currents
and
has
a 5 A or 1 A rating
primary
can
into
winding.)
be tested
them
time delay
by
injecting
to check
settings.)
their
wired
into the
usually via a special test plug/socket
the CT
relay. Secondary injection does not prove
performance
(as it is disconnected
during the test),
but
is the usual
method for testing an overcurrent
relay.)))
Marine Electrical Knowledge)
Practical
42
1115 2125)
At
81;1-: 82'0.: 83 0.\"1
.,)
\"..1&
R5)
R6
./
S)
R7)
03)
Current
setting)
,f.1
'.
CT
'-)
-
..,
1
T!{\037
.....S
Detector
and
curve
shaping
circuits)
Input)
{,2t'
.) ..
CM
SRS)
Trip and
alarm circuits)
urr)
R=\037______
C2)
--+r)
-ve)
1418, 1216
C)
2428
2226
A2)
ABB electronic overload
- Electronic
2.32
Figure
overcurrent
circuit)
relay
is critical
up of an overcurrent
relay
so
is
in
carried
out
strict
protective
duty
accordance
with the manufacturer's instructions.)
The
relay)
are typically rated at 2-3 timesthe
current to withstand
the
large
Motor
fuses
to its
motor
full
Fuse Protection
current surge (up to 5-7 times full load)
starting
of the motor. The motor manufacturer
will specify
the correct rating
of fuse
link for a particular motor
A
setting
fuse
most common
is the
a short-circuit
against
fault
rating.)
type of protection
in
LV distribution
circuits, motor circuits and portableappliances.
It is relatively
and reliable.
simple, inexpensive
As re-wireablefusestend to be less reliable
than
the
cartridge
type and are open to abuse
size of fuse wire),
are not
they
recommended
for marine practice. HRC (high
- eg 80 kA) cartridge-type
fuse
rupturing
capacity
links are normally used. A typical
construction
is
(fitting
shown
overcurrents.
as
In
of a fuse is its
25%
HRC
An
overload,
to small
insensitivity
event
the
fault
must
fuse link
.
will blow at currents as
but only after about 4 hours.)
- faster than
Fuses
are fitted
a circuit
breaker.)
three
one
The
others
them
protection
reference
include
the
small
overcurrents
overcurrent
A
starter
is
(eg due to shaft overloading
where necessary,
an
provided,
by
overcurrent
against relatively
relay
small
undervoltage
to
protects
overcurrents.
provide backup protection for
and generators
Undervoltage
all generator
circuit
breakers.
(OCR).)
relay
the
against a short-circuit
the motor
The fuse links
supply
cables
fault.)
may be seriously weakened, which
unreliable
for future
use.)
physical size and type of fixing
An
arrangement.)
Protection
mechanism
(UVR) is fitted
breakers and some main
feeder
Its main function
is to trip the
release
breaker when a severe voltagedip
occurs.)))
supply,
after a fault.
current
against short-circuits.Protectionagainstrelatively
on a motor)
in a three-phase
is found blown
symbols used on an HRC fuse link
rating, voltage, application
transformer,
diode,
general
use),
The
(eg motor,
to provide
in circuits
fuses
all
makes
fault current
replaced
even if only
replace
fuse
The advantage of a fuse is its very high speed
of
few
at
short-circuit
operation
(a
milliseconds) high
is
of a fuse blowing, the cause of the
be located and repaired beforethe
the replacement fuse link must be of the
correct current rating,
and type. Usually
grade
this means the replacementfuse link is
to the blown fuse link
identical
.
2.33.)
Figure
A disadvantage
low
.
to note about fuses:)
points
Important
the wrong
in
load
(around
50%)
Electrical Distribution
')\
[.)
......... .)
Live side clamp)
.,.;..
.,t.
,\037.
>
I
\\,',
I .
.,)
,\
\037I
,
43)
..\037
'-)
\037\
-)
Load side clamp)
i\
Fuse assembly
(DIN rail mounted))
-------
..)
*)
. ')
...)
Glass tube fuse)
/
/)
..\\)
Fuse holder
(shown In open state))
I..)
Fuse integrity
check points)
___________i)
DIN rail mounted fuse assembly)
Network terminal)
Screw cap)
. /....)
Colour coded
pop-out
indicator)
Securing cartridge)
Load terminal)
Cartridge fuse)
Screw cap)
Load conductor)
- ..
Glass window)
\"'\037)
\":1
\037
:
,[
:L '.
-<
......
Network conductor)
j \037)
Colour coded
-:- ; .......)
fitting
Melting wire)
Diazed
Figure 2.33 - HRC
This is achieved
the trip
mechanism
contacts
and
Securing cartridge)
(BoU/e) fuses)
construction)
fuse
releasing
by
the main
(which keeps
element)
contacts
the
mechanical
latch
to trigger
closed)
the breaker main
the load from the power
The UVR on a generator
circuit breaker
source.
prevents it being closed when the generator
voltage is very low or absent, and therefore)
that
disconnects
prevents closure of the
dead
generator's
circuit
breaker.)
opens
As shown in Figure
powered via
the
2.34,
safety
and incorporatedinto
breaker,
protection.)))
an undervoltage
release,
circuits of the generator
the
generator's
circuit
also provides overload and reverse power
Marine Electrical Knowledge)
Practical
44
220 VAC from Generator's power circuits)
Attracted
Coil)
Incorporated
contacts)
armature)
\037)
.)
45,\" R 61
LB/. .789OM
m\"..
. LVZ4)
-1UA16)
c..,)
Overcurrent relay)
'\" <0) 0> ..... v
.: :'\037
-. 3WX3153
fJJOO
RC unit)
-:-
AC220/230V\037
3WN
-1 FV01)
...... \037N)
3
\037. '
4503)
5
8)
J
-1 UA09)
Reverse power
-1Q01
relay)
r-----)
20
21
2
5
8
16)
3
UVR)
Siemens
I
ACB 3WS Undervoltage
release
generators' circuit breakers.)
Siemens
2.34 - Undervoltage
Figure
for
Siemens
ACB 3WS Undervoltage
A generator
off-delay
and
busbars
connection
diagram.)
protection)
QUESTION)
A three-phase
release
\037WS)
short-circuit occurs on the main
the short-circuit trip of the running
during
UVR is often off-delayed (by means of
which prevents spurious tripping
units),
transient
%
dips (typically 15 ) caused
voltage
by large
motor starting currents.)
2.9
Electric
how
generator breaker fails to operate.
Explain
the undervoltage relay providesa backup trip.)
ANSWER
short-circuit
reduces the busbar voltage to
which
causes
the U/V release
to trip the
The
zero,
breaker.)
Undervoltage protection is also required
The starter contactor normally
for
protection
as
it
out
drops
voltage is lostor is drastically
circuit will
not
when the voltage
special automatic
normally
provides
when
the supply
reduced.
The
allow the
supply
starter
motor to restart
except when
is restored,
facilities
restarting
are provided.)
of generator
Checking and calibration
undervoltage
releases can only be carried out accurately
by
calibrated
variable
voltage injection. A known
is directly applied across the undervoltage
voltage
release
terminals
\302\267The
voltage
\302\267the
voltage
to check:)
at which
at which
the UVRs coil pulls in
it
drops
cables
have to withstand
a wide
Ship
wiring
variety
of environmental conditions. Improved
materials
have
led to ship wiring
cables
of a fairly
standard
that are safe, durable and efficient
under
all
design
conditions.)
starters.
this
motor
Cables)
out.)
The normal distribution
on ships is 440 V
voltage
and
cables
for use at this voltage are designated
600/1000V, ie 600 V to earth or 1000V between
conductors.)
systems require cables with
eg for a 3.3 kV three-phase
earthed
neutral system, the required cable rating
is
V. For three-phase insulated systems,
1900/3300
Higher
voltage
ratings,
appropriate
the cablerating
would
be
3300/3300
V.)
are of annealed stranded copper,
circular or shaped. Cables with
conductors
and cores are usually smaller
shaped
and lighter
than
cables
with circular cores.)))
Cable
conductors
which
may
be
ElectricalDistribution
insulation
Cable
the
has a thickness appropriateto
rating. Insulation materials are
QUESTION
voltage
system
generallyorganicplastic
What is the purpose of
rubber,
Butyl
compounds.
which is tough and resilient,has goodheat,
ozone
and moisture
resistance.
However, it has now been
The sheath of a cable
from damage - it is not
as
(XLPE),
shown
at high temperatures
at 150\302\260C), and hardens
(melts
and cracks at low temperatures (-8\302\260C). Even
become
example,
the gland
PVC tends to flow and
temperatures,
distorted under mechanical stress - for
occurs at cable glands, causing
necking
its watertight
lose
to
Multicoreshipwiring
identified
either
by
cables
have
the cores
printed
numerals
untaped cores or numberedtapes on
taped
(PCP or neoprene) is a common
has been largely superseded
Polychloroprene
sheath
but
material
by chlorosulphonated polyethylene (CSP or
CSP-HOFR
is
hypalon).
sheathing
compound
well suited to shipboardconditions.
It offers
good
resistance
to cuts and abrasions, resistsweather,
acid fumes
and alkalis, and is flexible.)
ozone,
mechanical
Extra
with
armouring
non-magnetic
sheath
cores.)
The
phosphor
bronze.
wire braiding
interference
communication
compacted
stranded
conductors
XLPE
insulation
Cold easy strip semi-conducting
with the insulation
screenextruded
Copper tape
Cores laid up with
polypropylene fillers
Extruded
PVC bedding
Steel wire
armour
Black
..
*
. -
'-. .
,. .
*
t'
-- -
:---
*
\\' .
.\037
t\037-
.:\"\",
\037
..'
<\037-\037
.>-.
_._C\"- -
>
---
\037
-
-,)
Figure
2.35
- XLPE
cable construction)))
. .
.
I
J
\037-
--=-, \037
outer
braid.
also acts as a screento reduce
by magnetic fields) in adjacent
instrumentation
circuits.)
(caused
and
Round
I
The
properties of phosphor bronze are
for single
core cables. A protective
of CSP compound coversthe wire
preferred
on
is provided by
wire braid of either
protection
basket-woven
galvanisedsteelor tinned
properties.)
colour,
(HOFR).
flexible.)
in
used as an insulant
has
but
inferior mechanical
and thermal propertieswhen
with EPR. Polyvinyl
chloride (PVC) is not
compared
used
for ships' cables, even though
it is
generally
and flow
very common ashore. PVC tends to soften
at normal
on a cable?)
the insulation
as an insulant.
to be heat,
oil and
chemical resistant and flame
retardant
The sheath must also be tough
and
is also
2.35,
protects
classed
Sheath materialsare required
resistance to moisture and ozone. It should
not,
be exposed to oils and greases.)
however,
Figure
sheath
the
ANSWER)
rubber
largely superseded by ethylene
propylene
electrical
and
(EPR) insulation. EPR has similar
rubber
but with better
properties to butyl
physical
Cross-linkedpolyethylene
45)
PVC
oversheath
Marine Electrical
Practical
46
Knowledge)
A special
is covered with PVC for weatherproofing.
termination is used with MIMS cables to provide a
QUESTION)
Will cable
materials
insulation
moisture-proof seal for the hygroscopic
by a
powder. For an MICCcable,this is achieved
on to
compound-filled brass pot screwed directly
2.36.)
the copper sheath, as shown in Figure
burn?)
ANSWER)
All organic materials will eventually
burn in
a severe fire. Cable sheathmaterials
commonly
in use are organic plastic compoundsthat
are
classed
as flame retardant, ie will not sustain
a fire. Most cable materialsnow
achieve
this
Yes.
property
to
fumes
is the current the
without
the conductor
exceeding 80\302\260Cwith an ambient air temperature of
45\302\260C(ie a 35\302\260Crise).
This rating must be reduced
exceeds 45\302\260C
(de-rated)if the ambient temperature
or when
cables
are bunched together or enclosed
The current
by developing chlorine gas and acid
smother
the flame.)
However,
produce
feature for fire-fighting
personnel.
burning cable materials still tend
dense black smoke.)
a cable
continuously
in a pipe
or trunking, which
reduces
cable current ratings are based upon
PVC is notorious for its release
of deadly acid
fumes, but PCP and CSP do the same. EPR
and XLPEdo not. Somenewer
materials
do
- an
not produce acid fumes when burning
important
of
rating
cable can carry
sheath
cooling.
MICC
a copper
of 150\302\260C maximum.)
temperature
all types of cable, the size of conductors
for a particular installation is estimated
from
current
tables issued by suppliers.
rating
These
tables show current ratings for a range
of
For
required
to
conductor area and
cable types,
volt-drop/amp/
metre.)
MIMS Cables
Mineral
insulated,
are very
useful
These cableshave
as insulation with
(MICC- mineral
(MIMS)
fire-risk areas.
temperature,
oxide
powder
usually copper
which)
covered),
a magnesium
a
metal
sheath,
insulated,
from the main switchboard
cables
to the appliance must not exceed
6%
(in practice
it is about 2%). The cables installed
must
comply
with both the current rating
and
the volt-drop
limitation. Cable volt-drop only becomes
a problem
The volt drop in
cables
sheathed
metal
in high
copper
in
Copper sheath
Screw-on
brass
I
I
I
,)
pot
very
long
cables.)
PVCsleeve)
;
Compound
\\
I
,
\\
i
I
/)
\\)
I
i
I)
/)
. ,)
. \302\267
..
*)
\302\267
\037
':t <'.
.'
. .)
.
... ..\037. ..
'.
-)
. .\037
.. ,.
. .-.
.' ., .\".
. ., '. .... :. \".
.
...
.
\" .
.:.
.\".\037.. .....!..
.. .
-:-...
\". .
,.....
.. -!...)
. \" ,
\302\267
..... t
-III ....
.4
_,-.)
\302\267
.
..
III
......',,)
I')
.
.)
.)
\"
. \"\", .'
-.\":
.)
*
\\)
/
/
Figure
2.36
- MICC
cable termination)))
Cable
sheath
\\)
screw
to pot)
Disc)
/
I
Copper
conductor)
Distribution
Electrical
is the
What
purpose
overheating. Periodic
of localised
a source
QUESTION)
maintenanceshould
the
checking
cables are
include
always
tightness of terminal
terminated in terminal
of a cable gland?)
47)
Small
connections.
blocks.)
ANSWER)
should be periodically inspected and tested,
checking their connected appliances.
resistance
should
be measured
Cable insulation
Cables
are insulated,
Cables
mechanically protected
and
may be armoured
in a hazardous
explosive
these properties
maintains
and watertight.
They
suitable for installation
area. A cable gland
where the cable is terminated
box.)
eg at a motor terminal
an
at
appliance,
when
ideally
and the value
or a faulty
of mechanical
damage
the ingress of water. Cables
a heating current from
by injecting
injection set or a welding transformer,
cable gland is screwed into
terminal
box. Nuts
on the gland
the
appliance
compress sealing
on the inner and
seals
the armour braiding.
watertight
rings to maintain
outer sheaths and to clamp
The gland must be matched to the size and type
of cable. A typical
Ex-protected
gland construction
an equivalent
(which is more complicatedthan
2.37.)
industrial
type) is shown in Figure
In most
earthing of the cable
is by the cable gland. Where cables
cases,
armouring
pass
through
and fire-stop
bulkheads
watertight
barriers, they must be speciallyglanded to maintain
the
of such bulkheads.)
integrity
to
sockets
can be soldered
Conductor termination
the conductors but are more frequently crimped
tool.)
onto each wire by a compression
Cable sockets must be securely attached to the
screw
by nuts and shakeproof
applianceterminal
washers. A loose
will invariably
terminal
become)
a
permitting
gland
can be
The
and
in exposed
Cables
recorded.
damp situations,eg decklighting,
may
develop
low insulation resistance. Usually this is a result
out
dried
a current
in
shown
as
Figure 2.38.)
The procedure must
further
the cables, which
cause
The cable should be disconnected
from equipment
and connected as
ends
cables
must
shown.The injection
connections at each end. Current
satisfactory
be made
should
check
final
have
good
flow
and
cable
should be carefully
monitored.
When
insulation values have been restored
,
temperature
a
in
could
damage.
both
at
out carefully
carried
be
to overheat
not
order
normal ambient
the
with
cable
at
temperature.)
The injectedheating
never
must
current
exceed
- it is advisable
the rated current
for the cable
to
use an ammeter and to start at the lowest available
setting on the injection
be in the
region
the current
measured
\"
\037)
set.
The
of 30 to 55 V
voltage
depending
should
upon
setting. The cable temperaturecan be
with
a contact
thermometer
secured to)
l)
.,....,')
I)
\037)
\037
I
'*)
l....)
r A)
'
11-)
//
/)
/
,./
/)
,,/
/)
/
Compound
filter)
Figure
2.37
- Exd cable
gland)
1O-ring seal)
\\
\\
----1)
Armour
clamp)
Cable
clamp)
Cable)))
48
Practical Marine
Electrical
Knowledge)
Supply
Short-circuit
from
welding set)
link)
.)
-..)
-----J)
Two-core
cable)
Supply from
Short-circuit
welding set)
links)
--
\037
---=-----./
--\037)
--)
C
Three-core
2.38
Figure
- Cable
dry-out connections)
the cable or with an
be allowed to exceed
and
Temperature
measured and
sensor
infrared
a temperature
insulation
recorded
resistance
every
hour.
and should not
rise of 30\302\260C.
should be
When the
insulation resistance becomes steady,
heating
be carried out for a further
four
hours
before
switching off. Final readings of at least 20 MO
to earth
and 100 MO between cores should
be
should
expected.)
to cables must be made
the damaged
section
repairing
damage
good
by
with
adhesive
that
section
Unprotected
metal
heat-shrink
of cable.
tubing
In
the
case
or by replacing
of a partial cable
is also
replacement, adhesive heat-shrink
tubing
used for reconnection to an undamaged cable.)
armouring
and
insulation
material are vulnerable to attack
by moisture,
live
chemicals and corrosive gases, while
exposed
are clearly dangerous. A temporary
conductors
and binding
repair
may be effected by preparing
adhesive
the damaged section with a suitable
plastic electrical insulating
tape.)
repair of this type will
A temporary
Mechanical
either
cable)
acceptable
in
a
hazardous
zone.
not
be
Permanent
cable repairs must be madeas soonas
possible.)))
Three
Chapter
The
electrical
vary
according
on board ship will
ship type and its day-to-day
to the
To meet
(at sea or in port).
power demand, two or more main generators
needs
operational
An emergency generator, typically
100
250 kW at 440 V or 220 V, will be diesel
fitted
with
an automatic
start facility.)
demand
power
the
are
are used, which
backed
up by an emergency
service.)
generator and an emergency battery
The
with
is described,
together
generators
The
transitional
power must
Generator
AC
main
Operation)
power,
power
ratings range from, typically,
2 MW at 440 V, 60 Hz AC or 380 V,
50 Hz AC driven by diesel,
steam
turbine,
gas
turbine or propulsion shaft-driven
movers.
prime
As the demand for increased electricalpower
installations
arises
(eg for specialist offshore
vessels and cruise liners), it is necessary to
Main
250
generator
typically
also
at
6.6
(HV)
voltage
kV, 60 Hz but
with voltages
kV and 11 kV
3.3
generators).
to supply
in
come
immediately
the emergency
essential
general
without
intermediate
Battery
recharging.
from lead-acid or alkaline cells are usually
are
24 V DC.)
45\302\260
90\302\260)
I L)
------\037)
\\{)
-\037e\037-)
\\ \\
\\
S)
N
,_.JY\"'Y'YL:
;)
!
I
v
vL
I
;;;..\037
\037 IT
\037
?0
\037(l).:s
\037\037
q.'li \037\037VJ
J
/)
Phasor
rotation \\
e
....,
IL
q-'li
\037)
\037\037J
\037)
(lags
\037------)
I
r))ffI
/.)
L
\037)
W
One
Figure 3.1 - Principle
of generator
line diagram)
operation)
alarm,
and navigation aids, the fire alarm
system,
to supply
etc). Its capacity must be sufficient
these essential consumers for a periodof at least
30 minutes, during
which
time the battery voltage
must remain within
:t 12%
of the rated voltage,
radio
used.)
Rotor
the
of electrical
source
and
automatically
construction.)
battery which,
of the main
consumers (emergencylighting,
kW to
generate at high
will
operation
as
of emergency electrical
a storage
of failure
event
into
source
(either
a generator
or as
while the ship is under
be
and
of emergency
up to the power of the
increased
be
driven
supply
mode
the power ratings
generatorsmay
kW to
can be used during
emergency
generator
in port for the main
power
Therefore,
switchboard.)
3.1
time
a harbour generatorin single
in parallel
with one of the main
breakers and the main
of main circuit
a review
The
Note:
lay
protection and
operation,
construction,
maintenanceof generators
Breakers)
Circuit
Main
and
Generators
\\{)
Phasor diagram
(One phasehighlighted))))
bye))
supplies
rated
at
Marine Electrical
Practical
50
vast
the
As
(sometimes
Knowledge)
majority of ships use AC generators
called alternators),
the principles and
operational features will
this
cover
type
The two basic
relationships for
only.)
and
emf
dictate how to control the voltage
output of a generator. In practice,
frequency
the
speed
the
generator's
maintained practically constant by
The basic principle of
AC
an
An
rms
(emf) which,
is
An
into
induced
times larger than
eg if E is 440
rms
the
level,)
x 440:=
E MAX := 1.414
size
of emf
magnetic
flux
The
of
other
0
out
Three-phase
colour
with
coding
in blue).)
the
are
windings
phase
connected to outgoing conductorscalledlines,
which
are coded
as L 1, L2 and L3.)
622 volts.)
generated depends on the strength
this flux
(dJ) and the rate at which
three
output line voltages (represented by VL)
the three output
line
currents
(represented
to create the three-phase electrical
by IL ) combine
The
and
cuts the coils, so)
E:=nxcp)
the
rotor
poles
of:
output
power
n is the rotational speed of
where
size of pole flux
The emf
poles.
with
of phase
magnetic
is 120
two phases.
labelledas U-V-W
The other ends of
then)
by the
windings are
of red, yellow
and white used on terminals and busbars. One
end of each of the three-phase windings is joined
to form
the neutral
point of a star connection
(often
the
colour-coded
V)
the
has three sets of coils, called
located in slots in the stator
generator
windings,
surrounding the rotating
induced in each phase
(E) is calledthe root mean
and all equipment
is rated in
or maximum,
is 1.414 (-V2)
level
(rms) value
A peak,
terms.
output frequency. The
size of generated
the
fixes
which
is
).)
AC
phase
emf level
useful
square
on the
mover,
(excitation
ideally, has a sinusoidalwaveform,
each stator phase winding.)
The
prime
constant speed then allows
emf to be directly controlled
coils of wire
force
electromotive
alternating
poles
3.1.)
in Figure
shown
as
stator,
is very
are driven
generator
simple. Pairs of electromagnetic
fixed
(by the prime mover)
past
frequency
and
P := -v3 x V L x IL X coscp
in
(w))
rev/so)
In a
The
V
load current
flowing
internal
An
at the generator terminals is
where I is the
calculation]
in the stator phase windings.
of (I x Z) occurs
due
volt-drop
available
- (I x Z) [phasor
voltage
:= E
phase
to the impedance Z of a phase winding,
which
made up from its resistance and reactance.)
is
star
any line voltage
connection,
up from two phase
V
The
-v3 factor
between
L
in Hertz) of the emf
is
of waveform cycles per second.This
on the rotational speed and the number of
f (measured
number
the
depends
poles,
phase
made
:= -v3
x V
pH
0
For example, if
voltages.
:= 440
V)
V pH := 254
V)
L
then)
so)
The
f:=nxp)
is
is due to the 120 displacement
V
The frequency
VL,
voltages, where
rated
conditions
values
of a machine always refer
(as stated
on the rating
line
to
plate).)
or)
f:= (NI60) x p
where n := speed
in revis, N:= revlmin
and
p := pairs
of poles. Related speeds and frequencies,
with the
number of pole pairs, are given
in table
3.1.)
Table
Pole Pairs
For 60 Hz
For
(p)
rev/min (N)
rev/min (N)
1
3600
3000
2
1800
1500
3
1200
1000
4
900
3.1 - Speed
and frequency
50
750)
for
pole
pairs)
Hz
is the phase
is determined
Angle
which
cp
angle between
by
the
types
load on the generator (eg lighting,
equipment
the
current
voltage.)))
pH ,
motors,
galley
etc).)
Coscp is the powerfactor
is typically
I
VpHand
of electrical
about
0.8
waveform
of
lagging,
electrical
load and
which means that
the
lags about 37
0
behind
the
Generators
and Main
Breakers
Circuit
51)
QUESTION)
COS,n
\\ \\
\037
\\,\\
,,\\'\\\"
o.
\" '
'\"
,,\"
\\ \\ \\ \\
\\
' . .0.8
If the
above
500 kW generator circuit breaker is
protectedby an overcurrent
relay (OCR) setting
of 125%,what will be the actual minimum
I
\\ \\ \\ III
I IND
,
0.7 0.6
level?)
current
tripping
1
\"\"-
\037\"-0.9
........
........
ANSWER)
-?'-0.8
\037-0.7
The full
==- -0.6
')
,......1
CAP
{ -1.5 1&
SA
overcurrent
the
factor meter)
A)
(SG) generator can be an
electric power from
shaft-driven
for extracting
method
efficient
3.2 - Power
is 790.5 A, so the
relay will trip at 125%:
790 x 5 x 125/100 == 988
\037
\037)
A propulsion
Figure
current
line
load
generator
main engine as the power is derived
from
cost fuel than
that
used
for an auxiliary
DG
The SG may be fitted
in-line
with the
directly
ship's
lower
unit.
QUESTION)
slow speed propulsionshaft
or, more
to
a
gear-driven up
higher speed.)
in Figure 3.2
The powerfactor
meter
shown
has its scale divided
into
two segments,
each
is the significance
of
calibrated 0.6-1.0. What
each segment?)
electric
a shaft
using
By
units
power
periods
maintenance
a reduced
sea
long
during
for short
operate
as the main
generator
An
upper half of the scale
load is inductive (IND) or lagging.
of the scale (with
negative
marks)
in the
indication
shows that
The lower
the
half
that the load is capacitive(CAP)
indicates
or
leading.)
V
at the output of the shaft
to
generator
a constant 60 Hz to the ship's electric
Such
consumers.
power
utilises an electricAC/DC/AC
in
==
J3
X VL X cos
At the
<p)
frequency
phase
a fixed
500,000
J3 x440
==
790.5
A)
means
temperature
The
speed
limits.)
regulator
as
converter,
rectifier stage, the AC
three-phase
is converted to a DC
controlled
inverter converts
shown
generator
voltage.
output frequency by
A DC link inductor
switching.
x 0.83
that the phase windings,cable
and
circuit breaker must
conductors
generator
this full load current
be capable of carrying
without
their
and
exceeding
(FLC) continuously
This
a frequency
3.3.)
Figure
P
'L
is
for
is set
%
the ship's full-away speed range (eg 70-100
).
This means
that the frequency must be separately
maintain
AC generator rated at 500 kW, 440
deliver
a full load line current of:)
frequency control as this
by the main engine, which
determined
regulated
A three-phase
at 0.83 lag will
no direct
it has
creates
which
of a shaft generator
disadvantage
apparent
is that
the DG
requirement.)
ANSWER)
An
of
source
passages,
only,
be
commonly,
The
thyristor
sequenced
coil
three-
the DCback to
is interposed
to smooth the
between the rectifier
and
inverter
normal current flow and act as a current limiter
the event of a short-circuit fault.)
in
switch is turned on by a
thyristor
current pulse to its gate when its anode is
with
to its cathode. The thyristor
positive
respect
is only turned
off when its current is
to
zero.
This is a problem for the
(approximately)
An
inverter
positive
reduced
of an auxiliary
diesel-driven
generator
electronic
(DG) is accurately managed by an
that maintains an almostconstant output
governor
over its load range.)
frequency
inverter
thyristors
when
inductive
load (typically
lagging).
In
this
case,
driving
about
into
0.8
the current
the
power
ship's
factor
continues to flow)))
Marine Electrical
Practical
52
Knowledge)
.---/)
Main busbars
3 x 440V;
/\"
Main
()
/)
/)
60Hz
engine)
)
J)
converter)
Frequency
Shaft
I
L-----J
c:..---_-=j)
Three-phase
generator)
Three-phase
DC
bridge
controlled
link)
rectifier)
p)
inverter
C7l)
.......)
\037
J--\037
A
K
- \037.))
\037I. G
Ship's
,-\037:))
;
t)
'\\
;. _-/\ )
,
,---
Frequency
Voltage
voltage
control)
regulator)
&
Frequency
control
\037
.)
j
------------------
kVAr
j
u)
control
'Set'
3.3 - Shaft-driven
in a
thyristor
point,
a zero
generator
compensator)
\037)
To overcome
the thyristor
after its voltage has gone through
causing disruption of the inverter
this problem,
current
it
in phase
the leading kVAr
instant,
match the lagging kVAr
the
must
compensation
(- Q)
and
to have
necessary
with its voltage
(+
Q) must
operating
regulating
its
DC
of the ship's load, so
be automatically
controlled.
is to include
a synchronous
inverter.)
3.2.1 Construction)
main
two
The
parts
of any
rotating
AC
machine
are
its stator and rotor.)
steel
fabricated
The
stator core and
in
its
stator frame supports the
as shown
windings,
three-phase
3.4.)
Figure
The stator
core is assembled from
housed in slots
with the windings
periphery of the cylindrical
laminated
around
steel,
the inner
core.)
compensator,
power factor is controlled by
field current.)
controlled
Cooling)
exactly
Overall, the busbar voltage is fixed by the field flux
in the
shaft
and the busbar frequencyis
generator
regulatedby the
Construction
Generator
3.2
is
The practical solution
motor, operating as a synchronous
whose
feedback)
control)
so that turn-off is automatically
achieved (line
at
the
end
of
each
AC half cycle.
commutation)
The addition of leading
kVAr compensation
to the
to
create
an
overall
power system
unity power
factor solves the problem.Therefore,
the
SG/
converter
must only supply true power P (kW).
At
every
Voltage and frequency
sequence.)
switching
Synchronous
voltage)
'Set' frequency)
Figure
load
P, -Q)
coils are interconnected (in the
to form three separate
regions)
with
six ends. These phase ends
phasewindings
are found in the stator terminal box, as shown in
The
stator
end-winding
Figure
3.5.)
Occasionally,
terminal
the
or star point
stator winding
in
only three terminals are available
box and, if this is the case, the neutral
is an internal part of the
connection
arrangement.)))
and Main Circuit Breakers
Generators
Exciter
stator)
1\\..111)
I\037.)
Automatic
voltage
.lI\"! \037)
regulator)
..,..,)
Terminal box)
.......)
. \\
Exciter
I)
rotor)
Main field)
..
. = \\
*)
.. ..)
Silent
rotor)
pole
*)
Air
filter)
...:)
Stator core)
\037
*
Rotating rectifier)
\
\")
\037
.,
)
\037)
Stator winding)
Figure
3.4 - Generator
construction)
.........\037_.
....IQ.)
1\
.)
.J.,\037)
..
\037
'I
-)
\\)
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.'
,.-'I\"\"'''''\037'
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.)
')
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\037:I:\\to\037\037\037c;;\037g)
':J,'P,'<9.'<=>\037\037)
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. \037-\037,
\037\037\037.)
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u)
v)
w)
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l')
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Figure
3.5 - Generator
.i\037\037
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y)
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terminal box)
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OJ ..)))
53)
54
Practical
The
main
circuit
Knowledge)
connected to these
electric power to
at the main switchboard.)
cables
outgoing
the
conduct
terminals
its
Marine Electrical
breaker
generator's
material
by a thin layer of insulating
the bearing pedestal. The pedestal holding
must also be insulated by suitable
bolts
earth
from
beneath
down
sleeving.)
The rotor
field
of
a main
excitation
from
AC generator
provides the
its electromagnetic
poles.
of rotor
are available,
Two constructional forms
shown in Figure 3.6.)
Salient
In normal
as
marine
for
generators.)
Cylindrical type rotors are generally
with
used
large
slots.)
brushes on a pair
Under unbalancedfault
the
prevent
(usually
the
eliminated
conditions,
is
shaft-mounted
slip rings.)
the
end)
a shaft-mounted
by
as shown in Figure
bridge
its
rotating
The diodes
3.7.
as a three-phaseAC/DC
Negative
are
assemblies
output
rectifier,
are connected
circuit.)
Varistor)
link diode)
:\037\\: .'\\ \"-
Positive link)
\037)
AC terminal)
.\"
,
.\037)
\037.1\037\\)
.....
I:)
\\. ...)
AC terminal)
\037\037)
Negative link)
bearing
\037)
\037-)
is electrically isolated)
I)
Pole shoe)
Positive link diode)
DC output terminals)
3.7 - Rotor
Figure
diode plate)
Excitation
winding
in slot)
connector)
Inter-pole
Rotor body)
* ,)
Rotor body)
-.,.
,,. :..,.)
*)
*)
Pole axis)
(\";)
*)
I)
\037)
......)
End windings /
Excitation
. .)
...
winding)
Salient pole (4-pole))
Figure
with
equipment
an AC exciter, with
by using
rectified
being
flow of shaft current, one bearing
non-drive
of
commutators and slip ring
bearings
problem may be severe.)
To
exciter
a conventional DCgenerator,oris static
(see
Section
3.3 on excitation methods), the DCexcitation
current
is fed into the field windings via carbon
of large generators are usually
to prevent
insulated
stray currents from
circulating
Unbalanced
through.
(stray) end-winding magnetic
flux
induces
an emf along the steel shaft. This
will
cause
a current
to circulate through
the
shaft,
and bedplate to produce arcing across the
bearings
of the oil layer.
bearingsurfacesand degradation
shaft
The
(main field) is supplied
an exciter. If the
To eliminate the maintenanceproblemsassociated
a brushless
contacts,
rotating
arrangement
All brush gear,
is usual for marine
generators.
power, high speed
(1500-3600
rpm) steam/gas
turbine drives. The excitation
are wedged
windings
into axial slots around the steel rotor.
Unwound
sections
of the rotor form
the
between
pole faces
the winding
DC from
volts.)
with
type
Cylindrical
rotor winding
The
The salient poletype has projecting
poles bolted
or keyed onto the shaft hub. Field excitation
each
windings are fitted around
pole. This type of
rotor
is used
with medium and slow shaft
speeds
(1800
rpm and below) and is the most common
arrangement
measuring
as a few
type
pole
the effectiveness of the
operation,
insulation
can be checked by
pedestal
its voltage
to earth, which may show
3.6 - Generator rotors, salient and cylindrical
Cylindrical
construction)))
(2-pole))
and Main Circuit Breakers
Generators
The
six diodes,
AC exciter output
main
the
into
on the shaft,
mounted
the
convert
then fed directly
DC, which'is
to
rotor field windings.)
generator
Heater
power
single-phase,
to the
supplies
are
supplied
from a distribution
normally
55)
220 V AC
box
local
generator.)
The AC exciter has its
on
its stator
three-phase
AC
fitted
own
DC field poles
while the rotor carries its
construction layout
that of the main
3.2.2
is
inverted
with
compared
Cooling)
10
%
of
the
generator
in the
heating
and
windings
magnetic cores of both the rotor and the stator.
This heat must be continuously
transferred
out of
the generator to prevent
excessive
temperature
rise causing breakdown of the winding
insulation.)
air circulation in a closed
circuit (to prevent
via an air cooler, is pressurised by a
Forced
ingress of dirt),
fan
on the
rotor shaft.)
factors
generated
emf
stator core, between rotor
air gap (a few millimetres)
and
poles
between
in the
ducts
ventilation
the
through
the stator and
rotor.)
Water
used
of the circulating air may
cooling
for generators with a large power
also
be
rating.
RTDs
such
as
Temperature detectors (often
Pt 100) are used to monitor
the temperature
of
stator windings, bearings and the coolingair/water
of the generator.
Single or grouped temperature
alarms are activated
at
the
main
watchkeeping
position.)
While
the
forming
may
during
standby
or
low power electric heaters
the
machine
internal condensation
prevent
on the winding
insulation. These heaters
within
auxiliary
is stopped
generator
maintenance
be
periods,
switched
contacts
on manually or automatically from
on the generator circuit breaker.)
The water cooling system on a largegenerator
is
out
of service
due to a faulty
inlet
valve.
How will
this
affect
the generator
operation?)
ANSWER)
The generator can only be used to supply a
to keep)
much reduced electricalpower
output
for the production of a
are rotational
generator
regulated to maintain
the load power
continually
as
voltage
demand fluctuates.)
are either rotary or static.
utilises an exciter, which is
and
rotates
with the main generator
most
common
is to use a
arrangement
methods
Excitation
A
method
rotary
The
exciter.)
AC
shaft-mounted
In some
applications, a small additional
rotary
pilot
exciter may be used to supplycurrent
to the main
exciter field. A pilot exciter
is a small permanent
AC
that
is
driven from the
magnet generator
generator shaft.
Its
output
(eg
1000
DC before being fed
into
frequency
high
A
Figure
3.8.
carbon
dust
The
is generally at a
is changed
to
Hz)
the main exciter field.)
voltage
but
this
is shown in
of brushes, brushgear and
reliability and considerably
scheme
excitation
brushless
absence
improves
reduces generatormaintenance.Rectification
of
the AC exciter voltage is achieved by six shaft-
silicon diodes that form a three-phase
rectifier.
The suppression varistor
rotating
connected
across
the main generator field protects
mounted
the diodes againstvoltage
sudden
changes
the machine
QUESTION)
be
must
excitation
the generator output
shaft-mounted
through
AC
an
in
speed (n) and magneticflux (lP). Field windings on
the rotor create strong magneticfield poles when
direct current is passed through
them.
Various
methods
have been devised to supply
the correct
DC field (excitation) current to producethe required
AC output
voltage from the stator terminals.The
rotor.
air is forced
Cooling
essential
two
The
generator.)
Power losses, typically
rating, cause internal
Methods)
Excitation
3.3
output windings. This
exciter
in
excitation
arising
current.)
surges
temperatures belowtheir
from
maximum
emergency doors in
the
air cooling ducts may be opened
generator's
in such
The penalty is that
cases.
the
normally
closed air circuit of the generator is now
to
open
the engine room atmosphere.)))
permitted
levels.
External
56
Electrical
Marine
Practical
Knowledge)
Generator's 3 ....PH
voltage
II)
feedback)
AVR)
- .--1)
Generator
Rotor
Frame)
PH current feedback)
Generator's
CT)
components)
L1)
,---------------------------,
I
I
L2)
c::_
i
I
I
I
\\
i
I
I
I
I)
I
_\037
Exciter
stator (DC)
Exciter
Rotating
(3PH x AC))
Surge
rectifier
suppression
rotor
L3)
Stator)
Main
field
(DC)
varistor)
3.8 - Brushless excitation
Figure
scheme)
QUESTION)
What
QUESTION)
is likely
to
if
happen
of the
one
rotating
diodes fails and becomes:)
factors govern the overall
voltage
sudden
of
a
to
response
(transient)
generator
What
load
(a)
an
(b)
a short-circuit?)
changes?)
circuit?
open
ANSWER)
The main opposition to changes in
ANSWER
(a) The remaining
continue
healthy
to supply the main
the total field current,
AVR
be
will
voltage,
the
control,
would
diodes
field,
although
and so generator
slightly reduced. Under
exciter field current would
boosted
to maintain
the
be automatically
correct generator voltage, while the diode
failure would probably be undetected.The
exciter
will
overheat.
gradually
A short-circuited diode is moreseriousas
it leads
to a short-circuited
exciter. Rapid
(b)
overheating
the generator
of
the
will
exciter
lose
will
occur
and
excitation.)
current
required
voltage
are:)
.
Inductance of main
.
inductanceof exciter
.
automatic
voltage
diode failures are rare, somegenerator
are fitted with an electronic detector
systems
to give
an alarm and/or trip signal
to the
field
relay
generator's
occur.
field
affected
circuit breaker should sucha fault
the detector monitors the exciter
whose
size and shape is noticeably
Usually,
current,
by
a diode
failure.)
Generators with rotary exciters,
conventional
or
brush less, have a relatively
to
sluggish
response
sudden load changes. For example, it may take up
to one second to correcta 15% voltage
dip caused
motor.)
by the startup of a large pump
field
rotor
field
field
winding
winding
response.)
regulator's
The transient voltage response of a generator
can be improved by eliminating
the rotary exciter
in favour
of a static excitation method. In this
the generator field draws its DC
arrangement,
current
via a static excitation transformer/rectifier
and
unit
fed directly from the generator voltage
known
current
This
is
as
output.
arrangement
as
compounding
Although
the
to correct the generator output
it
is controlled
by voltage
(shunt
feedback.
effect) and current (series effect)
second
to
correct
times
as
low
as
0.1
Response
a 15% voltage dip are common with
static
excited
This
fast
compound
response is
generators.
desirable
where
heavy
and
frequent
load surges
arise from the deck machinery. However, despite
method
is utilised
advantages, this excitation
less frequently on board than
the
method
rotary
explained
in
the
paragraph
above.)
Static excitation equipment may be located
the generator casing or insidethe main)))
within
This type of generator has two
shaft
and brushgear to connect the static
to the rotor field winding.)
equipment
switchboard.
rings
slip
excitation
The
capacitors.
manual
trimmer
of a self-excited compounded
scheme
basic
generatoris
in
shown
operation is shownfor
Note:
3.9 (single-phase
Figure
is
and
voltage
On no load, the generatorexcitation
is provided
of the excitation
transformer.
by the PRI.1 winding
On load, the generator current injectsan additional
excitation
via PRI.2 of the transformer,
to
current,
a constant
If the
voltage.
output
excitation
the generator
components are carefully
designed,
voltage of a compoundedgeneratorcan be closely
at all
maintained
manual
or
AVR
loads
manual
for
synchronising
use
of an
addition
may provide
the load range and
This
over
of the generator voltage, eg
and kVAr load balancing between
control
excitation scheme
as reactors and)
static
excitation
associated
generator.)
/------------------,
systems
Automatic
3.4
require the static
Voltage
Sudden
load
starting)
on
change
current
surges
(eg due to large motor
a generator
cause a corresponding
its
in
voltage
drop
the effect is usually
load shedding will
busbars. An
This is due to
voltage.
output
the
in
generator
called
an
windings
or non-compounded
not
be realistic
unregulated
excitation system would
generator
on board ship due to the varying
load
demand.
by the fluctuating
regulation (AVR)
such
An
AVR
:t 2.5%
is necessary
equipment
changes
voltage
caused
voltage
Automatic
voltage
to rapidly
(see Figure 3.11).)
the generator's voltage to
of
its set value
over
the full load)
(or better)
will control
\\)
breaker)
,)
Excitation
\037)
transformer)
\037---------------I
:
PRI.2
:)
Flux
I
link)
'
Rotor)
Tl
+)
'
:
\302\253
Flux
-)
link)
( :'
I
I)
MaIn
Bridge
rectifier)
Slip
I
,)
Figure
rings
and
brushes assembly)
3.9 - Single-phase
compound
excitation
L________________)))
I
/)
circuit)
and
voltage
dip. Similarly,
an overvoltage
at the
produce
Main
Stator)
its
match
Regulation)
such
components,
I
or
will
an adjustment to the field
the resulting voltage surge so
output voltage remains practically
to closely
componentsto be designed
correct
three-phase
practical
has additional
surge
back
Compound
generators.)
A
the
that
quickly
internal
trimmer. However, some
do include
an AVR and
in such a compounded
rheostat
a manual
trimmer
static excitation
scheme.
closer voltage
regulation
allow
the
without
voltage
generator manufacturers
no AVR
has
current
load
A
constant.)
excitation
the
that
derived from the generator output
its current.)
maintain
3.10
Figure
simplicity).)
means
compounded
in
regulator.
57)
to correct
excitation
The
circuit
feed
automatically
Main Circuit Breakers
and
Generators
I
busbars)
Practical
58
Marine Electrical Knowledge)
I \037------------------,
Main busbars)
\\
I
I
I
I
I
I)
Excitation
transformer
Main
breaker)
--------------.,
1--------')
1
Stator)
:
1
........,)
(PRI.
2)
1
1
1
1
1
L_______J)
Reactor
coils)
Rotor)
W .
+)
(:
-
'-'\\
1/ I .
\\\\ t../
r
I)
Slip rings and
brushes
assembly)
I
,------------------_/)
Figure 3.10 - Three-phasecompound
I
I
I
f
I
I
I
I
I
I
I
I
Bridge
rectifier)
circuit)
excitation
(])
(])
Q)
t))
co
\037
\037
100%
(440
\037
V))
\037)
15%
max.)
I
I
I
I
I
I
\037)
..)
1.5
__________J_______
sec.
max.)
Voltage
'dip')
Time)
Time)
A VR response)
Unregulated
(no A VR))
Figure
- Generator/AVR
3.11
range. This is its
steady
voltage response)
state
voltage
regulation.
Transient voltage dip is usually
limited
to 150/0 for
a specified sudden load change
with recovery
back to rated voltage within
1.5 seconds.
In special
cases where unusually
are expected
large
surges
and cargo cranes),
the generator/
(eg from thrusters
AVR
limits may be extended.)
performance
The AVR
senses
acts to alter
the
the generator
output
field current to maintain
voltage and
the
voltage)
at its set value.A manual
be fitted on the generator
voltage level
More
commonly,
eg
440
trimmer
regulator
may
control panel to set the
V.)
two voltage
trimmer
potentiometers are assembled.Oneis inside the
into
generator's
panel and the other is incorporated
the control
card of the AVR.
This
more
option
gives
to personnel
for adjusting the generator's
flexibility
voltage.)))
manual
External
Main Circuit Breakers
and
Generators
59)
voltage trimmer
fitted))
(if
\037
/
--------
---------------
-----
\037R.
---------------\037
.
H
.
Comparator
Amplifier
.
Voltage
sensIng)
\037
Thyristor
J)
\037
G)
/
control)
'Set' voltage)
A
K)
-
-
'------)
--_/)
\
AC supply from
rotary or static
exciter)
DC field
3.12
The
control
- AVR block
generator,as well as solid state elements, mounted
on an electronicmodulefitted into the generator's
board.)
termination
complete
the
control circuit design varies with
the basic scheme contains the
AVR
the
manufacturer,
elements shown
in
Figure
driving
circuit
field
regulating
s).)
thyristor(
is a fast acting electronicswitch
controlled
by a voltage
rectifies
Additional
and
regulates
components
includedin the
.
Rapid
.
fair current
.
.
AVR
signal at its gate terminal.
the generator field current.)
and sub-circuits
to ensure:)
time
response
with voltage
are
stability
and reactive load (kVAr)
sharing
are to be operated in parallel
when
generators
quick
voltage
overvoltage/undervoltage
buildup
during
generator
alarm/trip
run-up
protection.)
and
stable
performance.)
feedback control system. However,
that, after replacing a faulty
AVR,
assembled
AVR
It
should
unit
checks,
running
compared
previous
generator
are
adjust
preset
such
a
bear
in mind
the
newly
be adjusted.)
as guided
by the
DC voltage
and
at installed test points.Theseare
measurements
with
to
with
always
manufacturer, consist of AC
range
A thyristor
resistors
variable
You should resist the temptation
controls unless fully competent
3.12.)
rectifies
The voltage sensing unit transforms
down,
and smooths the generator output
voltage.
This produces
a low voltage DC signal that is
to the AC generator voltage.This
proportional
a set DC value
DC signal is compared with
actual
diodes
circuit
of
zener
a
reference
produced by
from
the
An
error
resistors.
and
output
signal
made
suitable
for
and
then
is
amplified
comparator
the
is fairly
circuit
AVR
includes a few preset
control of sensitivity,
to achieve an optimum
Although
60Hz
complex and
for the
offset
error and stability
and differential control).
integral
(proportional,
These are adjusted and set during generator trials
The
of
consists
and current transformers, mounted on the
voltage
V,
output)
diagram)
for a modern AVR
circuit
x
3-)
\037
v)
Figure
3 440
,)
G
current
values
usually
found acceptable
trials. The voltmeter
during
type and its
for
test.)
each
specified
Mostships will carry a spare AVR unit or spare
a suspected
cards that may be interchangedafter
should
failure. An AVR
only be
changeover
attempted when its generator is stopped and
at the test pointson the new
off. Checks
locked
AVR
field current level and the manual
excitation
operation
(if fitted) should be proven with
regulator
the
generator
running on no load before attempting
on to the busbars.)
to synchronise
are
load sharing
When
generators
check
sharing
for approximately
equal
the machines.
between
correct
of their AVRs.)))
operation
in
parallel,
current (or kVAr)
This will
indicate
Marine Electrical
Practical
60
Knowledge)
QUESTION)
What
must be taken when testing
of generator
cables
and wiring
to an AVR unit?)
the insulation
connected
load)
under
Running
precaution
Q1)
ANSWER)
Electronic
such as transistors,
components,
capacitors,integrated
circuit
thyristors, etc, are likely
a high
test the
generator
electronicparts,
either:)
Short-circuit
all
during the IR
\302\267 remove
.
Ship's
load)
Q2)
(500 V) megger test. To
its cables
to earth and protect the
voltage
and
.
to
Incomer)
(ICs),
be damaged
during
chips
cable
outgoing
terminals
- Two
3.13
Figure
generators to be synchronised)
test
electronic
card(s)
disconnectall cables
separately.)
achieve
smooth
incomermust
be
To
at both
ends and test
manual
brought
synchronising, the
to obtain
up to speed
approximately the same frequency
is shown
that
on
the busbar frequencymeter,eg 60 Hz.)
QUESTION)
Main
generator
or diesel drives)
share
in Parallel)
Generators
3.5
units
(gas
have
to
turbine, steam turbine
be run in parallel
to
a total load if it exceeds
a single machine.Changeover
standby
generator
units
What
are the likely
consequences
to close the incomer'scircuit
requires
a smooth transition
without
blackout.
For simplicity
and security, it is
not normally
to
run
a
main
in
possible
generator
with either the emergency generator or
parallel
a shore supply
in cases
where the ship's
(except
to allow this type of
powerplant is constructed
interlocks
are used to
operation).Circuit breaker
prevent such an arrangement.)
Parallel
in
the
two
are usually
operations
automatically,
manual
but
is generally
auto control.)
use
and
At the
instant
phase
difference
smoothly
synchronised
the voltage
the breaker,
a large
circulating
prime movers,and
each
the
generator
current
circulating
breaker.)
large
is set
by its AVR
to
carried out
control
is still
provided as a backup
in
common
the
to
the incoming generator,
with the live busbars.)
parallel
causes
current between the machines,which
produces
a large magnetic force to pull the generator
voltages
(and field poles) into synchronism.
This means
rapid acceleration of one rotor and
deceleration
of the other. The large forcesmay
the generators
and their
physically
damage
Fine
of the speed can now
be observed
on
tuning
the synchroscope or synchronisinglamps.The
incomer
is adjusted
so that the synchroscope
indicator
rotates slowly clockwise (fast direction) at
about
The
indicator
be
closing
The incoming generator voltage
be equal to the busbar voltage.)
The generator already on the bars is calledthe
machine
and the generator to be brought
running
into
service
is the incoming machine.)
To
of
of
stages
synchronising and load sharing.)
Both
voltages are not in synchronism?)
generator
may trip
is achieved
running
of attempting
the
when
ANSWER)
the capacity of
of main
and
a brief parallel
to achieve
period
running
breaker
it
must
4 seconds
per indicator revolution.)
breaker
circuit
approaches
should be closed as the
the 12 o'clock (in-phase)
position. The breaker closingbetween
5-past
the 12 o\037clock
satisfactory
slow.)))
synchroscope
5-to
position
as long as the pointer rotation
and
is
is fairly
In each
QUESTION)
the
synchronised
optimum
The incoming generator ammeter pointer
show
very little kick when correctly
will
synchronised.)
equally
is usually
type synchroscope
to
20
to
minutes) avoid
(eg up
Do not forget to switch it off after a
traditional
as it displays
bright.)
pointer
short time
QUESTION)
rated
overheating.
How could you
procedure.)
paralleling
or synchronising
light
phase difference
generator
the
between
up to show the
ANSWER)
voltages.)
.
lamps
.
sequence
a voltmeter, as shown in
(expect
up to 500 V on
behindthe doorof the
the front
dark method
bright
Connect
(2
method
a 440
Figure
V system)
3.16,
across
one pole of the open incoming generator circuit
breaker. This procedure is moreeasily
(and
at the synchroscope terminals
performed
safely)
methods:)
Lamps
lamps?)
a circular
use
As a backup,or alternative,
to the synchroscope,
a set of lamps may be used. The correct
synchronised position may be shown by either of
the following
monitor the correct instant
for
the aid of a synchroscope
without
synchronising
Modern synchroscopeindicators
set of LEDs that sequentially
.
in Figure
3.15a,
a rotation
of lamp
whether
the incoming
brightness that indicates
machine is running
fast
or slow (anti(clockwise)
the lamp
clockwise). As with the synchroscope,
clockwise.
sequence must appear to rotate
slowly
Correct synchronisation
occurs when the top or
key lamp is dark and the two bottom lamps are
ANSWER)
A
case, the lamps are connectedbetween
and the busbars. The
generator
is preferred
condition?)
lamps)
circuit
of
the
diagrams
main
panel
synchronising
before
such
at
Check the
switchboard.
testing.)
(2 lamps)
(3 lamps).)
method)
L1
L2
L3)
Busbar
Incomer
volts)
volts)
Incomer
'\\IIIII
V
500
\",,\037\"''\\
\037\037\"300
\037........
i--zoo
t:
\037
-0
...:E:)
c:\".1G1
\037
coscp
\"'\037
0'k'\037:\037l\037
.....\037\"t
\037'.o.a
\037'().8
t:\037::
,.
eN'
.
.-\037'1(!)
..\"1i.
S:
Synchroscope)
...
:::)
\037)
Busbar
, F)
EG
generator)
(V)
3.14 - Synchronising
instruments)
-
i,i,i.i,i.:,j;i. i,,,i
II:1' illl'lI \",:,i. :II
G1)
G _ G2)
Incoming
..
I 'IIIIIIII\037IIII
I hml
V
1 J:1II11II\037'rI1ll1
1[-'010 II t.)
frequency)
frequency)
Figure
61)
incoming
sequence method,as shown
is available to show the
indication
What
Main Circuit Breakers
and
Generators
,
SG)
ISOL)))
Hz)
\"1:-\".10
:5)
Marine Electrical
Practical
62
Knowledge)
the
L1
L2
L3)
')/0'-')
Circuit
breaker
watch
keeper,
;/)
a permit-to-close
allows
only
\\F
angle and frequency of the
with respect to the busbars.
is initiated by the
operation
but the check synchronisingmonitor
phase
generator
voltage,
incoming
conditions
synchronising
limits. This
signal when all
are within
the
acceptable
method provides a useful
safeguard
overall
error, but retains
operator
against
watch keeper
control for adjusting the voltage
and
frequency.)
lamps
Sync.
(sequence
method))
Auto
synchronising
an
everything
of an incoming generator does
would do. It senses
and
controls
the voltage and frequencythen
circuit breaker close signal at the correct
Incommg
generator)
Figure 3.15a - Synchronising
operator
three
with
initiates
a
instant.
The auto synchronising equipmentuses electronic
circuits
to monitor
the size of voltage, frequency
lamps)
and phase angledifference,
them until
they
are
equal
then
acts to regulate
to the existing busbar
conditions.)
Adjust the generator speed until the voltmeter
very
Close
slowly fluctuates from zero to maximum.
the breaker when the voltmeter
through
A
check
Figure
indication
Usually, the check or auto
switched between a set of
passes
zero.)
are
and when
units
synchroniser
as
generators
required.)
synchronising
has
3.15b,
unit, as shown in
an electronic circuit to
monitor)
.1.
'. . \" .
\"')
..
. '!\\
., \"
.)
.
\".
...
. ..,.
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TER NB.230
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r
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ill
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r
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3.15b
-
Synchronising
unit)))
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Figure
;.
A-..
',-,p.;\037)
,,_
r;
i
I
I
14; 2O.-.Lj
t\037
\037_\037
.... 11'
tU.T.,.,...,....
...............
\037\"I
\037II-
is achieved by
load sharing
kW
Manual
Main busbars)
Main Circuit Breakers
and
Generators
63)
raising
machine
setting of the incoming
while
machine.
lowering the setting on the running
The balance
of power sharing is dictated
by the
the
L1
L2
L3)
L)
: t'
OfF
,;
. --)
:. .
mover.
Current
voltage
droop
is set by
generator AVR.)
(or kVAr) sharing
of each
the
For equal load sharing of kW and kVAr, each
machine must have similar droop characteristics,
which
2-4% between no-load and
are
typically
...)
C\"'Vvo......
.. 6.. ,.
\037..:.\037,)
A.
o
droop of each generatorprime
(speed)
governor
fl'LUKI,
1\"-..\037)
n..\037.)
Lt,L1
I)
I .'.-.r.,r
'\
governor
values.)
full-load
\\.)
\037)
An
Incoming
generator)
Figure 3.16 - Synchronising
with
a voltmeter)
comparing
meters of each
generator.)
equipment
The
the
synchronised,
total
load can now be shared
busbar
to the
a
operation,
parallel
generator
while
its
directly controlspower
(kW),
new machine.
governor
synchronising
should be switchedoff.)
between generatorsor totally
transferred
or
connections.)
Manual load sharing is the normal
control equipment fails.)
fallback
if the
auto
now
are load sharing in
generators
1 delivers
PQS
(from
power triangle):
Q == P x tanqJ1 == 500
x tan36.9\302\260
== 375
parallel:)
500 kW at 0.8 power factor
(b))
and)
Generator
tanqJ
2
==
== ---.\302\243
Q
-350
P2
400)
==
0.875
so
2 delivers
400 kW
kVAr lag.)
350
and
({J2
== 41
.2\302\260
then,
pf 2 == COS({J2
Calculate:
(a)
the kVAr
(b)
the pf of Generator2
(c)
the
loading
busbar
total
of Generator
loading
== 0.75
1
ANSWER
in
kW,
kVAr
==
so
qJ1
.2\302\260
Lagging)
+ 400
== 900
and
Total Q == 375
Overall tan({J
and
qJ
==
+ 350
-Q == -725
P
900
== 38.9\302\260)
so,
== 36.9\302\260)
kW)
and
(c))
COSqJ1 0.8)
== cos41
Total P == 500
power factor.)
(a)
kVAr
factor'.)
Generator
lag,
and
of each
checkingthe tightnessof the
QUESTION)
Two
kW
factor (cosqJ)
In
AVR trimmer controls reactive power (kVAr)
'power
power
sharing equipment compares the kW
generator (via CTs and VTs) and
is used to provide an error signal
any difference
to
raise/lower
the governor
setting of each prime
mover
as necessary.
The equipment is usually
trouble
little maintenance
other
free,
requiring
than
an occasional
visual inspection, cleaning and
an incoming generator has been
successfully
the
Autoload
loading
When
of load sharing for
balance
overall
can be seen by
overall
load pf == cos38.9\302\260
== 0.78
Lagging)))
== 725
==
0.81
kVAr)
kVAr
Practical Marine Electrical Knowledge)
64
normal
In
are load sharing equally in
generators
when
a
total
loss of excitation
occurs
parallel
No.2 machine. What is the likely
outcome?)
called
the transfer
However,
when
with
No.2
run
will
an induction
as
generator, drawing its excitation kVAr from
No.1.
Both generator
currents will rise rapidly
with No.1 becoming more lagging while
No.2
runs with a leading pf (indicated on coscpmeter).
A loss
of excitation
trip (if fitted) or the
overcurrent
should
relay
trip No.2 generator
probably causing an overload
No.1.
on
Result
main
undervoltage.)
the
emergency
and
generator
generators
needed.
if
run
in
parallel
in this
Therefore,
for
power failure, the emergency
of main
event
the
In
it
as
DG units.)
main
generator
mover
prime
The run-up is initiated
should
start
an
electrical
by
automatically.
relay that
normal voltage supply (eg 440 V)
of the emergency switchboardwhich,
is connected to the main
operation,
via the transfer line.)
the
side
at
the
in
normal
switchboard
- total power failure!)
are moored at a
generator can
vessels
cargo
situation, synchronisation should be provided
also offers a reduced maintenancerequirement
monitors
No.1 trips on overcurrent, which
Alternatively,
No.2
of excitation and its breaker trips
deprives
on
a feeder
line.)
berth, for example,
be used as a harbour
Generator
board is
by
in
ANSWER)
out
main
the
from
supplied
Two
the emergency
switchboard
operation,
QUESTION)
to
Falling mains voltage causes the startup
relay
the emergency generator prime mover's
operate
starter.)
3.6
Generators)
Emergency
cranked
mover may be electrically
prime
24 V battery and starter motor
its own
The
from
The powerrating of an emergency
generator
is determined by the size and role of the ship.
On smaller vessels, a few kW will suffice for
and more
emergency lighting
only.
Larger
or
complicated vessels, such as LPG carriers
liners, may require hundreds of kW for
passenger
emergency
lighting, re-starting of the main
engine
auxiliaries
and to supply firefighting
pumps.)
construction
The
generatoris
similar
and operation of an emergency
to that
of a main generator.
either
static or rotary,
will
Excitation
supplies,
usually
be governed
by
an
automatic
voltage
regulator.)
will
at 440
operate
usually
switchboard
will
room 440 V main
be
V
and
interconnected
in normal
switchboard
A
manual
in
the
operation.)
is
not
normally
possible
emergencyand
main
interlocks
control
in
the
breakers, at each end
prevent parallel running.)
to synchronise
the
Special
circuits of the circuit
of the interconnector,
generators.
own
or,
for
hydraulically-
may
startup
the
Weekly
be initiated
by
room.)
of
production
of the
testing
includesimulation
can be achieved
the
buttons
of
by
auto-start
equipment
of emergency
power.)
the
is
emergency generator should
loss of normal power. This
off a transfer line
switching
the
circuit breaker at the side of the
turn,
push
generator
emergency
to
generator engine.)
emergency
Correct functioning
vital
emergency
switchboard.
main
switchboard
will
be
blacked
as a result, automatic
of the
starting
emergency generator should be initiated
along
with its circuit breaker switching to supply the
out and,
emergencyconsumers.)
generators
Emergency
checked and run
to comply with
running
It
to the
locally
the
emergency
with the engine
its
from
driven hand starter and accumulator reservoirfitted
In
Generally, the emergencygeneratoroutput
voltage
is at the same level as that
of the main generators,
AC. In an HV/LV
eg 440 V, 60 Hz, three-phase
system,
eg 6.6 kV/440 V, the emergency
generator
be started
example,
checks
up
safety
should,
be regularly
for short test runs
These
no-load
regulations.
should
to speed
when
practicable,
be
supplemented occasionallyby an actual load
test. This requires the disconnectionof normal
mains
power from the emergency board while
the
is loaded up to near its
emergency
generator
rated
value.
the
Only a proper load test will prove
of the emergency generator,its prime
performance
mover
and the circuit breaker operation.)))
by the
determined
Protection)
Generator
3.7
Main Circuit Breakers
and
Generators
65)
overall protective discrimination
scheme.)
Other than
direct
through
temperature
functions
relay
increases
the
with
together
level and time
by
relay
adjacent
via a special multi-pole
(usually
to the relay and internally
Chapter 2 for
circuit
general
Overcurrent
Inverse
The OCITrelay
function
balanced
in
NPS
the
Sequence
4
4
relay
stator
currents,
A
generator stator and rotor temperature.
small
of
unbalance
causesa
relatively
degree
increased
rise, so the
significantly
temperature
NPS current setting is low at around 0.2 x In.)
settings)
..)
'\\
;)
,J
G
Thermal
\037
monitor
,
/ trip
Alarm
EL)
\037
\037
I
.
.........\037
(inst)
NPS)
\037e-
breaker
RP
UF/OF
.......---
1-
circuit
,
UV/OV
-
I
Generator
(--
.......
.......
Fault trips
I
IU<I
.......
.......)
LO
\037
.......
\037
3 -
Figure
3.17
- Generator
DIFF.)
I
,
OCIT
OC
-Q1
(NPS)
the amount of unbalance
which is an indirect
measure
determines
of the
4
4
3-
Phase
Negative
general
--
are:
ranges
t==0.1-1s.)
generator
overloading and has current/time
(HV system)
against
extremely
by a short-circuit fault.
protect
and
(OCIT)
NER
to
caused
1\302\273==2-10xln)
3.17.)
monitors
trip
setting
Typical
An
Time
Os.)
overcurrent
high
methods.)
for
current))
to it). See
wired
Some typical relay types employed
are outlined in Figure
protection
generator
(INST)
socket
protection
or rated
'Instantaneous'
may be grouped
case.
relay
Settings for
must
be periodically checked
and/or voltages directly into
currents
injecting
the
OC
functions
delay
1 -1
t ==
a single
within
are:
and
rating and voltage level.Electronicprotective
inside the generator's main
are mounted
relays
switchboard
Protection
can be also provided
panel.
the
circuit
breaker
PLC-based logic
by
generator's
module.Someprotective
(t)
1>==0.7-2xln
(In == normal
kVA
generator
for current (I) and time
ranges
setting
Typical
of the stator windings and the
internal
of a generator is largely
air, the protection
on the sensing of current and voltage from
based
CTs
and VTs. The number and type of protective
measurement
Main busbars)
protection scheme)
Alarm
system)))
Practical Marine Electrical Knowledge)
66
Differential
This is a OIFF measurementof
at each
current
for this very serious fault
settings
0.1 x In.)
low, eg about
Earth
An
EL
sequence) detectsan
very
returning
connection. In a
the earth fault
neutral
transformer,
(NER), or earthing
current
is
pick-up
setting very low, eg
time delay of 0.1-0.5s.)
resistor
1.2.Un
current
earthing
so the
1-5A with a
Also
be required in many
protection
voltage),
function
may
not
schemes.)
are
settings
(UF/OF)
typically
system) .)
Lock
Out
(LO)
or
Power Protection (RP)
intended
generator should be inspected
insulation and tightness of
for signs of oil and
of cable insulation within
.Check
to
operate
in parallel
must
have RP.)
RP relay monitors the direction of power
flowing
between
the generator and the load. If a prime
mover failure occurs, the generator
a
An
acts as
motor.
The RP relay detects this fault
breaker.)
trip the generator circuit
water
terminal
that the cooling air intake
contamination
boxes.
exhaust
and
and are free of dirt
Inspect and clean the generator rotor and stator
a dry, lint-free
cloth.
windings
by removing dust with
Low pressure, dry compressed
air may be used to
dislodge heavier dirt, but be careful not to drive the
dirt
deeper
cleaner
Generators
to the
relay
trip/hand-reset
alarm.)
and
acts
to
pick-up power level setting and time
delay
are adjustable
and are preset to suit the
setting
mover. If the prime mover is a turbine, very
prime
little
is absorbed
when motoring and a
power
reverse power pick-up setting of 2-3% is usual.
If the
mover is a diesel, a setting range of)
prime
The
wiring
are not blocked
openings
and dust.)
the
circuit
responsible for tripping
generator
breaker. Its action is instantaneouswhen
triggered
also be used to trip
by a protective relay. It can
the
generator
prime mover, and initiate
generator
field suppression
of an
together with the signalling
Reverse
All
Check
This is the master LO
that
switched off and isolated.
or frayed
damage
terminal
connections.)
58 Hz and 62 Hz for
a 60 Hz system (48 Hz and 52 Hz for a 50 Hz
UF/OF
that the generator
off, auto-start circuits
electric
heaters
are
ensure
is locked
are disabled and
for
Over Frequency
and
Under
(Un
== rated
breaker
circuit
gear is
inefficient operation.)
and
the generator
prime mover is
locked off before you begin any
and
down
failure
maintenance
control
associated
their
that
ensure
Always
the correct
and
inspection
Regular
shut
(UV/OV)
with settings of
delays of about 2s. A UV
with time
a
Maintenance)
Generator
of generators and
essential to prevent
Overvoltage
monitored
are
functions
UV/OV
around 0.8.Unand
is easily checked during
operation
relay
maintenance.
and
Undervoltage
of
current
fault
neutral
HV generator system,
ship's
is limited by a high
impedance
range
delay
breaker.)
3.8
earth
earthed
the
time
A
The outgoing generator is
generator
changeover.
so that it motors,
throttled
down
causing
gradually
the reverse power relay to trip its generator
circuit
called zero phase
(sometimes
back through
RP
The
(EL)
Leakage
relay
are
adopted.
about 0.5-3s is usual.)
end of a stator phase winding.
This
comparison
of current is to detect an internal
fault
in the
stator windings, which may be caused by partially
short-circuited
coil turns and/or earth faults.)
Current
is usually
5-15%
(DIFF)
into the windings. An industrial
vacuum
is very effective for removing
dirt from the
coated
nozzle
windings. Use a rubberor plastic
on the vacuum cleaner tube to prevent
abrasive
to the sensitive winding
insulation.
Oil on
damage
the surface of winding
insulation
will reduce
the
insulation resistance and shorten its life. The oily
the windings
deposits can be removed by washing
with special slow or fast drying
degreasant
liquids.
Minor abrasions
repaired,
suitable air drying
Brushless
to winding
after cleaning, by
insulation
insulating
generators
can
the
application
varnish.)
be
of a
usually require less
maintenance.Generatorswith
static
excitation
systems
require additional care. Rotor
slip
rings
must be checked for uniform
wear
and that
(even)
the carbon brushes have free movement
in their
boxes. Correct brush pressure can be checked)))
spring balance and then
comparing
the manufacturer's instructions. A pull of
around 1-1.5 kg is usual. If the brushes
become
too short (below about 2 cm),the reducedspring
will cause
pressure
sparking at the slip ring contact.
with the correct type and bed them
brushes
Replace
of the slip rings.This can be done
to the curvature
using
a pull-type
a thin
IR value
based
may be acceptable to a surveyor
on 1 kO/volt, eg 450 kO or 0.45 MO for a 450 V
it is the historicaltrend of the
However,
generator.
machine
IR values that
will provide
a better picture
value
of the insulation
paper (not emery
its cutting surface
paper)overthe slip
under the carbonbrush. Pull the glass paper around
the slip ring until the brush surface has the same
contour
as the ring. The last few passes of the
glass
direction as the
paper should be made in the same
by placing
strip
of glass
with
ring,
normal rotor direction. Remove all
dust with
Generator
components
A special
oil and dampness.
contact
dirt,
grease
is used between the diode connections
to prevent
action
between dissimilar
electrolytic
occurring
After
the
windings
to earth
(assuming
neutral
disconnection at the
.)
circuit
box).)
or short-circuit
to disconnect
Remember
electronic
damaged
by
the wiring
diagrams
a high
that
are
likely
electrical
With
all
and
dampness
- dirt,
equipment
overheating
are. the enemy!)
Main Switchboard)
3.9
instructions before testing. Recordthe IR values
and note the prevailing temperature and humidity.)
A
main
ship's
3.18.)
typical
Figure
switchboard
is shown in
3 X 440V, 60Hz MAIN SWITCHBOARD
3 x 440V - consumers
Gen. 1
Gen. 2
Synchr. panel
.
Ib1
.1
.e.' _\037 ...
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-.\037
IS]
....-
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0 I...
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-e L\037
I, I , I , I , I !I , .
I
.
\037II ! I . I , I :
l il ,l jl ll i
-
Figure
3.18
II II , I ,
I I I I I i 1 11 ,
.
.
- Main
.
I I
.
M
-e
....
.
.
I
(g
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10
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switchboard)))
.!J
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.
.
.
.
.
.
.
.
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3 x220V consumers
3 x 440Vconsumers
Gen.3
I
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IS]
should
load,
any
to be
insulation
test.
Consult
voltage
and the manufacturer's
components
On
its insulation.)
is available for
point
terminal
checks
stator phases
and between
the
that
running
loading.
-e
I I
-e
-e
-.
L!J\037
.
-e
-e
\037L
.
I I
I I
I I
.
.
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.
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.
I I
I
.
.
I I I \037
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1
I
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I
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.
it
if a generator
is to be left idle for a long
Finally,
are suitably
time, make sure that its windings
heated to prevent internal
condensation
forming
do not disturb
of the stator and rotor
insulation
Measure
drying
high
1
i
\037
---'
.
is
to check for excess temperature rise and
when running in parallel.)
stability
important
load-sharing
them unnecessarily.
no-load
maintenance,
precede synchronisingand
metals.)
.but
the
during
air drying insulating
varnish.
Should
the IR
quality
value remain low during
a dry-out,
the machine
insulation needs to be completelyreimpregnatedor
rewound
(generally
by a shore-based
workshop).)
of
tightness
steady
should be covered with
its windings
period,
excitation transformers, AVR
diodes must be kept free
and rotating
Checkcontactsfor
become
has
which
value,
of carbon
traces
condition.)
with very low IR values
Generators
than
(less
0.5 MO) should be given
a thorough
then
cleaning
dried out. If the IR has recovered to a reasonable
cleaner.)
a vacuum
67)
with previous
test results. A minimum
is usually taken to be 1 MO, but a lower
Compare
it with
Main Circuit Breakers
and
Generators
I
I
--.J
!J
.
.
.
.)
on
68 PracticalMarine
Electrical
Knowledge)
The central section of the main
used for the control of the main
switchboard
is
generators.
The
The electricaldistribution
diagrams
physical arrangement of the main
switchgear cubicles on either sideof the generator
panels are used for essential services and, flanking
are the grouped
motor starter panels.)
these,
layout.
are
HV systems), handles for
(including
doors on switchboard cubicles
panel's
cases
some
In
the
linked
usually
switch.This
be
that
Efficient
scheme.
component
key
fault finding
only be achieved
can
network
in
on a distribution
a thorough
with
of the scheme and its normal
understanding
are isolating switches that
fuses.
The action of opening the switch
incorporate
isolatesthe
that
can be replaced
they
isolators
fuses so
and controls for particular
For example,
has all the
panel
instruments
Switchboard
are
functions
opened.)
Fused
ship
your
operation.)
off before the door can
are switched
cubicle
the
in
to an isolating
to components
interlocked)
supplies
(or
ensures
the electrical circuit and
to identify, locate
study
and appreciate the role of each
the
opening
should
You
layout diagrams for
the
will follow
switchboard
together.
grouped
the generator synchronising
instruments, relays and switches necessaryfor
paralleling.)
generator
generator panel has all the instruments,
switches, controls and status lamps
for control of the generators. The
necessary
Each
safely.)
Fused isolatorscan alsobe interlocked
with
door handle. Motor starters frequently
relays,
the
instruments on panels of outgoing
circuits
are
usually limited to an ammeter, status lamps,
cubicle
this
incorporate
arrangement.)
switches
function
One type of interlockedfused
isolator
can be
and
removed
to ensure
completely withdrawn
complete safety when carrying
out
and push
manual/off/auto)
(eg
buttons.)
on
maintenance
equipment.)
control and instrument wiring
is of
small cross-section, with multi-coloured
insulation
that is clearly identified
plastic
against
the larger main power cables.)
Low
power
relatively
Maintenance on fused isolatorsconsistsof
the operating mechanism.
checking
periodically
Contacts must be inspectedfor
greased
electrical
an
with
mechanism (if fitted) should
correct and safe operation.)
section
A separate
220 V AC
low
near
engine
control
The main
main
the
mounted
and
lightly
The interlock
also
be examined for
switches the three-phase
and lighting
services.)
V lighting
440/220
The
power
damage
lubricant.
it
to
the
supply
cables
busbars
three
are connected
that
run
through
of the switchboard.The busbarsmay be
rear doors of the switchboard cubicle
are opened,but it is also possible they are in a
enclosed
busbar duct acting as an internal
special
the length
seen
fire
the
if
barrier.)
Take
care when opening doors on switchboards.
Live
parts
are
panel.Green
and
expos\037d
LV
ship's
of the front,
switchboard,
electrical
and
showing
will
include
drawings
of the main
fitted equipment.)
the rear,
the
breakers
circuit
generator
and other large
(600-6000
A) on board
of an air break type called
ship
traditionally
an air circuit
breaker
This means that the
(ACB).
circuit
breaker
contacts separate in air. An ACB
breakers
circuit
are
outline is shown in
3.19.)
Figure
6.6
High voltage (HV) installations, eg at
11 kV, generally
use the vacuum
interrupter
or gas-filled (sulphur hexafluoride -
kV
and
type
SF6)breakers.
Outlines
are
in Figure
shown
- you are in danger.)
diagrams
perhaps
Breakers)
Circuit
Main
distribution
In
The
yellow
instruments and panel doors,etc,is connected
to
a common
the
copper earth bonding bar running
of the switchboard at its rear. This
earth
bar
length
is electrically bonded to the ship's steel hull.)
3.10
circuit breakers.
Short
directly to their respective
circuit breaker
copper bars from each generator
connect
wiring is supplied
behind the appropriate
earth wiring from
striped
control
and
are located
that
fuses
transformers are generally
switchboard (often in the
room).)
generator
The instrumentation
from
a vacuum
by a few millimetres
level of a vacuum
the
vacuum
the contacts
interrupter,
be separated
sealed
is checked by applying
a
in
as
only
the
need
to
insulation
high. The quality
chamber
interrupter
short
duration
HV pulse)))
is extremely
the
of
3.20.)
(eg
10 kV for a 6.6 kV
across
breaker)
Figure 3.21 shows how
mounted on guide rails
the open
contacts.)
cubicle, from
In the
special
typically
gas breaker, the contacts separate in a
chamber containing SF6 gas,
interrupter
at 500
kPa (5 bar) at 20\302\260C.)
isolated
mechanism
operating
breakersis
that
to
similar
main
a main
be withdrawn
for vacuum and SF6
for an ACB.)
employed
and its guide rails are usually
mounted
cassette bolted into the switchboard
and electrically connected to the busbars.)
breaker
in a special
cubicle
Structure
Internal
Motor charging
1
and
busbars for maintenance and
from the
testing.)
The
The
breaker
switchboard
circuit
each
inside
it must
which
Main Circuit Breakers
and
Generators
{'......------
type
Stored energy type)
3)
19
!
------J)
1 - Overcurrent
2 - Arc chutes
GJ)
4)
5)
6)
trip device
3 - Isolating contacts of control
circuits
4 - Line-side main circuit terminals
5 - Draw-out
moulded
base
6 - Load-side main circuit terminals
7 - Isolating contacts of main circuits
8 - Fixed main contacts
9 - Moving main contacts
10 - Closing mechanism
11- Trip bar
12 - Inst. trip devices
13- CT (for overcurrent
(for marine use)
trip
14 - Charging motor
15- Closing latch release
18 - Quick-close/slow-close
selectorlever
19 - Auxiliary switches)
15)
3.19
- Air circuit breaker
device)
16 - Closing
spring
17 - Charging handle
-14)
Figure
(solid-state)
components)
Fixed
main contact)
Epoxy resin case)
Contacts
in vacuum
chamber)
Magnetic
*)
Metal bellows)
Fixed contact)
*. . -.,----
/)
.1)
'I)
.
-----
r)
coil)
Arcing
chamber)
I)
\\ ' .)
\\
Moving
main
contact)
*)
Ceramic
\\)
Moving
*-)
contact)
Operating
mechanism)
*)
Insulator)
I)
SF6
Vacuum Interrupter (one phase))
Figure
3.20
- Vacuum
and SF6 interrupter
units)))
SF6
Interrupter
gas)
(one phase))
69)
is
Marine Electrical Knowledge)
Practical
70
Front of switchboard)
Breaker
cubicle)
Circuit
Circuit
Main contacts
breaker
(engaged))
body)
Test
Circuit
breaker
disengaged)
body)
body)
Isolated
Figure 3.21 - Circuit
breaker
special hoist or fork
heavy duty units.)
The
action
that the breaker is to be
its cassette,
then a
lift is usually
required for large,
circuit
the
breaker
a safety shutter to cover the live busbar
contacts at the rear of its cubicle. The mechanical
linkage in a circuit breaker is quite complex
causes
and should not
be
interfered
maintenance and lubrication
man ufactu rer.)
The
main fixed
and moving
with except
for
as
by the
specified
contacts
contacts
are
of copper
normally
suffer
burning and may be
dressed by a smooth file. Carborundum and emery
should not be used - the hard particles can embed
themselves the
in
trou
soft
contacts
and cause
Arc chutes, or arc splitter boxes, confine
and
control
the arc to rapidly
accelerate
its extinction.
parts
must be removed and inspectedfor
of the splitter plates.)
and erosion
of different types of circuit
may be fitted.)
breaker
mechanism
manual
spring
The spring charge is directly
applied
by manual
of
the
handle.
T
he
last
few
depression
closing
centimetres
of handle movement releases the
to close
the breaker. Closing speed is
spring
independent the
of
operator.)
stored
Motor-driven
charge
for
spring
marine
Closing springs are charged by a
unit. Spring recharging is automatic
gearbox
closure
of the breaker, which is initiated
following
a
button.
This may be a directmechanical
push
by
releaseof the charged spring or, more commonly,
applications.
motor
an electricalreleasevia
stored
Manual-wound
This
latch.)
charge spring
stored charge
to a motor-driven
is similar
spring,but
a solenoid
with
manually
charged
closing springs.)
future
ble.)
These
closing
This is the mostcommontype
or silver
(sometimes of special arc-resistant
alloy
and
silver
coated.
Main
tipped)
usually
alloy
contacts
should
not be scraped or filed. If the main
contacts
suffer severe burning
will probably
they
require realignment.)
Arcing
A number
Independent
of withdrawing
position)
positions)
from
removed
completely
Remove
position)
demands
work
position)
Circuit
breaker
repair
disengaged)
body)
position)
Engaged
If
breaker
broken
Solenoid
The breakeris closedby a DC solenoid energised
from the generator or busbarsvia a transformer/
rectifier unit, contactor, push button
and,
sometimes,
a timing
relay.)))
Generators
are held
breakers
Circuit
position by
in
closed
or ON
The breaker is
the
latch.
a mechanical
this latch, allowing the kick-off
tripped by releasing
springs and contact pressuretoforcethe contacts
.
Circuit breakers
their
springs
for:)
.
Store
in
the
button or relay (such as an
contact and kick-off
circuit
springs.)
must be exercised when handling
when either the closing springs
care
Extreme
breakers
are chargedor
the
circuit
breaker
is in
the
position.)
main
if
still
circuit
in the
ON
ON
Care must be taken
force if the
breaker
be
to the
Electrical
circuit
Isolated circuit breakers racked out for
maintenance
should be left with the closing
springs discharged and in the OFF position.)
Tripping can be initiated:)
.
to
position.)
springs
.
a remote
electronic
relay).)
Mechanical interlocks are fitted
breakers to prevent racking out
closing
or relay
device
coil - when energised by
trip
overcurrent
store energy in
charge mechanisms
trip
(trips when energised)
push
WARNING:
71)
(trips when de-energised)
\302\267 overcurrent/short-circuit
\302\267 solenoid
open.)
release
undervoltage
Main Circuit Breakers
and
-
a push button
Manually
linkage trips the latch)
with
mechanical
not to exert
undue
will not move as damage may
switches
are connected into
control circuits to prevent incorrect
interlock
breaker
sequence operation,eg when
breaker
caused
interlocks and other mechanicalparts.)
a shore
supply
is closed onto a switchboard.)
The ship's generatorbreakers
are
usually
interlocked
OFF to prevent parallel running
and the shore supply.)))
ship's generator
of
a
Four
Chapter
The
ship
Starters)
and
Motors
on board
gears, mooring winches,
drive
power
for almost
(eg
thrusters,
cargo
all gears
pumps, compressorsand fans) comes from electric
motors, the mostcommonof which is the threephase AC cage rotor
because it is simple,
motor starters.)
reliable
Three-phase induction
at 440 V, 60 Hz (380
6.6 kV,
and requires very little
and stops with simple
and
tough
it starts
and
attention,
It is popular
motor.
induction
60
usually
3.3
supplied
kV and
used for bow
sometimes
Hz are
thrusters and
are
motors
V, 50 Hz), but
winding. The conductorbars are set in a laminated
steel magnetic core. The essential reliability
of the
motor comes
induction
from
this
having
type
of
simple, robust rotor, which usually has no insulation
on the conductorbars and does not have any
troublesome rotary contacts such as brushes,
commutator
or slip rings.
Figure 4.1 shows the
main
items
used
in the construction of a typical
fan ventilated
enclosed,
totally
(TEFV) induction
motor.)
gears.)
cargo
The rotor winding
consists
of copper
or aluminium
conductor bars that are connected
at
together
their ends by short-circuiting
to
form
a
rings
cage
on ships
include
types of motor found
DC commutator motors for driving
deck
machinery
where speed control is important,
and
single-phase
AC motors in galley
and domestic tools.)
equipment
Special
synchronous
power
High
used for
electric
propulsion
This chapter will
deal
AC motors are frequently
drives (see Chapter 8).)
motor,
three-phase AC cage rotor induction
with its control and protection.The more
together
of motor speed control methods
common
types
followed
are alsodiscussed,
procedures
maintenance
by
Enclosure
particles
is defined
by
a two
where
motor
has two main components,
carries three
the stator and the rotor. The stator
separate insulated phase windings
120
0
(electrical)
apart
and
lying
that
in slots
are
spaced
cut into a
laminated steel magneticcore.This type of stator
winding is similar to the construction used for an
The ends of the stator windings
AC generator.
in the stator terminal box, where
are
terminated
the
to the incoming cable from
connected
are
they
three-phase
the ingress protection (lP) Code,
figure number is used to indicate the
AC power supply.)
the ingress
against
of solids
and liquids.)
ventilated
open
of
valves may
induction
opposition
liquids. The enclosure protection
and
degree of protection
Drip-proof,
The
of its
for motors and starters.)
Motor Construction)
equipment is
to the ingress of
for electrical
protection
defined in terms
the risk
4.1
Ratings)
Motor Enclosures
solid
with the
principally
and
Enclosures
4.2
liquids
be
motors are used where
leaking from overhead pipes and
a problem.
Air is drawn into the
cooling. The
screens to
from entering
the motor and
prevent any objects
The
must
screens
causing damage.
always be kept
machine
by an
internal
ventilation
ducts
are
clean and free from
due
to inadequate
fan
to provide
fitted with mesh
dust
or the
motor
will
overheat
ventilation.)
When a greater degreeof
protection
is required,
and
No
the enclosure is made TEFV
jet-proof.
To improve
external air is allowedinsidethe motor.
to increase
heat transfer, the motor casing is finned
across
the fins is
the surface area, and airflow
fan and cowl
achieved by means of an external
arrangement.)))
Marine Electrical
Practical
74
Knowledge)
Terminal box
cover)
*)
Cover seal
gasket)
Links)
* \037..........
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Terminals)
__\037n\037n)
Fan cover)
*\
i
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-t.
Terminal box)
preloading
,,'
LI. 1f)
\302\267
....,. =:\037t
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'-, :,
I,
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*)
Stator frame)
\037
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J..:'
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----.
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, ----End shield)
Fan)
-- ,._
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Driving shaft
key)
Rating plate)
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End shield)
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ring)
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4
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./)
\037.)
..
..:.\".)
\037;.\"
...: .\037
I'; -:)
..)
\037\037\"
..)
J
,\":.
\" \037.\037
.....:j \"'.
.:\\
:.. I \"t..
1',
,; l'
. I:.I,
J .: '
.)
,:' j
j
\037)
\" \"..
.)
\"::.:
...)
/I.')
,'.
t:)
\"'--... \
.)
-'':'\037
. \" 'f\"
. .\037)
.\037:)
'-.)
..... .\037).,.)
't
..
\"\"....\037.\037. ..._t_)
'-:. \037..,f')
.....:)
\\-t\"')
,\037
\037\"\037
.\037\037.
.)
........
\037
\037..)
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\037..\037
'.t; .)
..40)
'\\'
\037\\')
-\", \037-\037
.......:\037)
:,,'--)
,.)))
Figure
4.1 - Induction
motor components)
and
Motors
Motors located outsideon weather deckshave
but the external fan is
enclosures,
watertight
omitted
because
of the possibility of ice formation.)
deck
, .11)
u'
'.'
Deck watertight motors
and a watertight
bearings
(IP56) have
box.
\037:.,
\\
,-)
sealed
terminal
Starters
They
,\037)
\\:
water
for
can be completely immersedin shallow
under
all
short periods. Sealing washers are fitted
screws
and a coat of special
corrosion-resisting
and internal
paint is generally applied to all external
\
\\
..')
\037
\
surfaces.)
Figure
of Protection
Degree
numeral)
the
No protection of equipment
solid foreign bodies.
Protection
contact with
for
body,
ingress
of
Protection
o)
No protection)
1)
Protection against drops of condensed water:
of condensed
water falling on the
Drops
enclosure shall have no harmful effect.)
2)
Protection against drops of liquid:
of falling liquid shall have no harmful
Drops
effect when the enclosure is tilted at any angle
from the vertical.)
up to 15\302\260
accidental
or inadvertent
against
live or moving parts inside
the
example,
against
numeral)
enclosure.
against
by a large surface of the human
a hand but not protection
deliberate
access to such parts.
against
ingress of large solid foreign
enclosure
1)
against ingress of liquids)
2nd
against contact with
No protection
of persons
live or moving parts inside
o)
of Protection
Degree
against contact with live or moving parts inside
the enclosure and protection
of equipment
against ingress of solid bodies.
1st
4.2 - TEFV motor enclosure)
bodies.)
Protection
contact
against
live
with
parts inside the enclosure
Protection against
ingress
2)
or moving
by fingers.
of medium
size solid
bodies.
foreign
Protection against contact with live or moving
parts inside the enclosure by tools, wires or
such objects of thickness
than 2.5 mm.
greater
Protection
against
ingress of small solid foreign
3)
Protection against
3)
with
4)
rain:
falling in rain at an angle up to 60\302\260
shall have no harmful
respect to the vertical
effect.)
bodies.
Protection
against contact with live or moving
parts inside the enclosure by tools, wires or
such objects of thickness
than 1 mm.
greater
Protection against
of small solid foreign
ingress
Water
Protection
4)
Liquid
have
against splashing:
from any direction shall
no harmful effect.)
splashed
bodies.
protection against contact with live or
the enclosure.
Protection
moving parts inside
of dust. The ingress
against harmful
deposits
of dust is not totally prevented, but dust cannot
enter in an amount sufficient to interfere
with satisfactory
operation of the equipment
Complete
5)
Protection against
5)
Water
projected
under
stated
have no
by
water-jets:
a nozzle
conditions
harmful
effect.)
from any direction
shall
enclosed.)
Complete
6
moving parts inside
against ingress of dust.)
Note
the
against contact with live or
the enclosure.
Protection
protection
that the higher the
greater
numeral
2nd characteristic,
degree of protection
6)
of the 1st and
7)
the
enclosure
Protection against conditions
(deck watertight
equipment):
Water from heavy seas shall
enclosure under prescribed
Protection against immersion
It must
not be possible for
enclosure under
IP55 meets all
IP22,IP23,
the
less
IP34
onerous
and
IP54.)
degrees such as
ships'
not enter
conditions.
decks
the
in water:
water
conditions
to enter the
of pressure
and time.
offers:)
Protection
eg Jet-proof
stated
on
against
indefinite
immersion
in
water
under
8)
specified pressure.
It must
not be possible for
enclosure.)))
water
to enter
the
75)
Marine Electrical
Practical
76
Motor
Knowledge)
Ratings
The motor converts electricalenergy taken
electric
from
power supply
at the motor shaft. Power lossesoccur
the
which results in
conversion,
during
energy
the
of
in
heat
the
motor.
The losses
production
the
mechanical
rotational
into
IArERT
energy
increase when the load on the motor
because
the motor takes more current
Type
.
the
from
su pply.)
life of the
The
on the temperatureat which
marine practice based on an ambient
of
45\302\260C. An
temperature
is
limit
4.3 - Motor rating
Figure
temperature
maximum
the
that
Standard
exceeded.)
not
Motor nameplate definitions:)
and their average
the
motor
without
supply
for the insulating
value
supply voltage.
exceeds
of
burnout
stator
the
voltage
supply
limit,
stalling
overheating,
and
the
motor
supply
frequency.
are directly affected
losses
If
is operated
it is rated at,
motor
the
at any frequency other than
overheating can occur.)
the
one
rating
This is the shaft
of the motor when it
output
power
to rated voltage and frequencywhen
its rated current from the supply.)
is connected
4.1 - Output
speed
This
is the full
Motor
Induction
the
three-phase
three
load
speed
voltage
of the
the resulting phase currents producea multi-pole
rotated
is physically
flux (w). This flux
magnetic
around the stator core by the switched
sequence
called
of the L1-L2-L3currents at a speed
of synchronous
speed (n s)' The value
synchronous
on
how
pole-pairs
magnetic
speed
depends
many
winding arrangement
(p) are fixed by the stator
and by the frequency
(f) of the voltage supply
connected to the
stator
Indicatesthe degreeof protection
given
by the
motor enclosure.)
rating
as
winding.
or
are shown
example
in
s
==
fx60
rev/min
p)
QUESTION)
What is the synchronousspeed of a 6-pole
motor supplied at 60 Hz?)
ANSWER)
details
in the
N
motor when
and frequency.)
IP number
nameplate
Operation)
AC supply voltages are
stator phase windings,
p
connectedto rated
The motor
39 64 90 125 162321780)
power ratings)
n s ==! rev/s
Rated
power
ratings
(FLC) for 4-pole,
11 22 37 55 75 100200500
connected to the
and
drawing
current
load
winding can result.)
speed
Power
full
7.9 20.1
3.1
1.4
4.3
When
by
AC induction motors are
60 frame sizes, with
power
0.37 kW to 500 kW. Table 4.1
of
Rated frequency
Motor
0308)
to operate
designed
successfully when connected to this
the rated voltage
1.5 4.0
kW 0.55
Table
the
2.08/1.2A
440 V motors.)
A
Rated voltage
If
from about
ratings
can continuously
take from the
exceeding the temperature limit
materials used.)
been
1.73/1.0A
label)
shows a sample selectionof output
Rated full load current (FLC)
This
is the maximum
value of current that
has
.
0.60HP
three-phase
in about
manufactured
The motor
81
0.50HP
for the insulation
lifespan
adequate
is based on the assumption
Nr.: 634518
it
for
selected
are
materials
E(B)
: 6/Y
on motor
used
materials
insulating
windings depends
is operated.
Insulating
3 - Mot
IP55
50Hz
220/380V
0.37kW
: 6/Y
220 1 440V
0.45kW
60Hz
: 6/Y
220-240V /380-420
50Hz
: 6/Y
60Hz
250-277V /440-480
0.78/0.71
2740/3400 min-1
cas;
Th CI
increases
MadeinEU
IEC 60034
71ZAA2
AM
on the motor
Figure
4.3.)
20 rev/s
or
1200
rev/min)))
The stator rotating
magnetic
rotor conductorsto
induce
togetherat
the
cuts
alternating
through the
emf into
How is the rotor
ANSWER)
currents
also produce a magneticflux
with the stator rotating
which
interacts
flux,
Simply
rotor
that
(T) on the
a torque
produces
as shown in Figure
conductor
rotor
bars,
is the
stator flux,
rotor cu rrent
is the
angle
is the
<P
IR X cosqJ)
The
rotor
reactance
flux,
which
depends
it
varies with the rate of cutting
on the rotor speed. Therefore,
accelerates
T == V2 (as
to
of the
direction
rotate
at
of friction
and
windage.)
([J ==
Vand
torque
'R
==
Slip speed is the difference betweenthe ns of the
rotor speed (n R ).)
rotating magnetic flux and actual
is
is usually
Slip
([J))
speed:
synchronous
rotor torque causes the rotor
s = ns
same direction as the rotating
in the
3-phase
AC
current
.
/
.
L1
.L2
.
.
.
L3)
. .
(
Stator
core
phase
windings)
100
\037nR
...N
'\\.
I
\037 I
I /)i'
.t
//,\037....-)
/
/
/
/
/
\"
/
i
\",.
\\)
.
Force
C
\\.;
/
I
i
, .
j I
I)
. .
t
\037
\
\037)
.\\)
....
Force
@)
(F)
\\\\')
\"
Rotating
flux)
\"
/ i
, /
..( )'
\037,
.\037)
......\037
--\037\037
'.....,
Rotating
stator
,,/)
......)
s)
Twisting
force
(torque
Figure 4.4 - Induction
motor
action)))
(F))
.)
0)
,. 'i
i
,. ,)
stator
%)
)X
and
I
./)
as a percentage of the
expressed
field.)
magnetic
normally
losses
rotational
mechanical
the
will vary during
motor
startup
is
up to its rated speed. If coscp
ignored (for simplicity) then the shaft
approximately
given by:
The
run
factor)
(power
coscp
([Jand 'R')
between
magnetic
synchronous
speed. This is because the rotor
conductors
would
then be stationary with
respect
to the rotating magnetic field. No emf would
be
induced in the rotor and there would be no rotor
current
and no torque developed. Even when
the motor
is on no load, the rotor speed has to
be slightly
less than the synchronous speed (ns)
so that
current can be induced into the rotor
conductors
to produce the torque to overcome
and
cp
cannot
motor
induction
An
where
'R
This
box.
fi e I d .)
4.4.)
T == CP x
any two supply line
over
swapping
by
connections at the stator terminal
reverses
the direction of the rotating
torque size is determinedas:
Rotor
as
reversed?)
direction
the
ends,
currents.)
The
77)
QUESTION)
conductors are connected
emfs set up rotor
induced
the rotor
Since
them.
flux
an
Starters
and
Motors
=
on rotor bars
F x
radius))
flux)
Practical Marine Electrical Knowledge)
78
At
QUESTION)
If a 6-pole
a slip
with
the
startup,
is
motor is suppliedat 60
of 5%, what is the actual
Hz and
rotor
necessary
load accelerate.
The speed increases until, at the
of the two characteristics, the torque
developed by the motor is the same as the torque
requiredby the load at that speed. The motor
and
load will then run at this steady
speed, as the
the demand.)
matches
torque supplied
exactly
runs
intersection
speed?)
ANSWER)
The synchronous
speed is 1200rpm,
rotor slips
of 1200,
by
5%
ie by
60
and
rpm
motor develops more torque than
to turn the load, so the motor
and
the
so the
rotor runs at 1140rpm.)
the rotor will
slip),which
to
to slow
tend
down (increasing
rotor conductors
the
allows
supply
no load and full
and
almost
5
%
its
three-phase
stator
current
of 5-8 times full-load
current
(FLC)
This is due to the maximum
rate
of flux
%
cutting (s == 100
) in the rotor creating large
is taken.
inducedrotor
small (between 1o\037
motors are considered to be
The
machines.)
is very
currents.)
is very
load
), so induction
constant
speed
indicates
drive the load at different
the
torque
necessary
supply power factor at startup
about
0.2 lagging,
which rises
corresponding
low, typically
to about 0.5 laggingon no load
0.85 lagging on full load.)
The characteristicin Figure 4.5 shows the
variation of torque with slip for a standard cagemotor.
Also shown
is a typical load
type induction
characteristicthat
motor is connected directly to
AC supply voltage, a very
large
induction
an
When
demand.
reduced,
Equipment)
the
to cut the
increased
rate. This causes morecurrent
in the rotor, which is matched by morestator
current
to meet the increased shaft torque
The
motor
will now run at this new, slightly
The fall of motor speed
between
speed.
flow
Control
4.4
is increased,
shaft
an
at
flux
on the motor
load torque
If the
This
to
starting
then
to about
surge current reduces as the motor
its running
speed.)
up to
accelerates
speeds.)
p.u.
torque)
2.5)
Max.
torque
point
(stalling or pull-out))
2.0)
Starting
1.5)
torque)
1.0)
Full/oad
runningpoint
0.5)
---
Figure 4.5 - Motor
----
----
0.25
0.5
0.75
1.0
0.75
0.5
0.25
torque/speed
slip)
--
o)
.-)
at 3-5%
:-.
- - .)
curve
and shaft loading)))
:1.0
0
p.u.
speed
p.u. slip)
at low power factor is
is relatively high,
current
supply
FR
resistive
causing
significant
(copper) losses.
The only way to improve the power factor of the
motor
on light loads is to reduce the supplyvoltage.
This
can
be achieved
with an electronic voltage
called
a soft starter and/or energy
controller,
Operating
on light
inefficient
as
loads
the
match
the supply voltage to
conditions.
Such a controller
manager,which
can
and
load
aims to maintain
the
the startup
as
to minimise
possible
losses.)
Note:
This
control shaft
if
the
are
may
of other
malfunction
the
in
electrical equipment connected to the supply, eg
lighting dip and flickering effects, and even cause
of unessential
consumers
tripping
by means of
undervoltage releases.)
the starting
bow thrusters,
current,
limit
To
(eg
reduced
voltage
voltage
reconnected
close to their
rated
large induction
motors
cargo gears, etc) are
started
and then have the full supply
when they have accelerated
speeds.)
starting option is also used.)
frequency.)
Relatively
result
Two methods of reduced voltage starting
by
are called star-delta starting and
switching
autotransformer
but an electronic
'soft'
starting,
controller does not
is controlled by
(which
speed
small
size induction
motors (up to 20 kW
is sufficient)
because such
from the main switchboard
power
on line (DOL) started
direct
startersare
and
inexpensive
maintain. The high
starting
simple
current
and
to operate
surge
will
not
initiated
stop/start push buttons.
the rated current
for the
out automatically
(OCR) to disconnect
(see Section 4.8).)
Coil
Moving
,)
section
perform
and
to connect
to
motor.)
the
is an electromagnetically-operated
switch
tripped
4.6,
Figure
disconnect the powersupply
three-pole
When large motors (20 kW and over) are started
disturbance
of
DOL, they cause a significant
voltage (voltage dip) on the supplylines due to)
ring)
in
action in starters
The contactor
serious
unless
heating damage to the motor
the motor is repeatedly started and stopped in a
short
time period.)
Phase shift
shown
as
Contactors,
the switching
cause
from
If the
motor,
by
the motor
an
local and/or remote
current goes above
its contactor
overcurrent
the
from
will
relay
supply
of
electromagnet
1)
Fixed
section
of
Return
electromagnet
Contacts
spring
assembly
\\)
I
I)
\\)
,
1)
I)
I)
-)
I
, .... .)
')
I
o)
1-)
...)
i:)
\"!\302\243
j)
Telemecanique
Figure
4.6
79)
current surge. This voltage
starting
large
disturbance
at
supply current and power
of voltage
type
power factor as high
operating
the
Starters
and
Motors
- Contactor
construction)))
LC1 D contactor
internal components)
be
80 PracticalMarine
Electrical
Line
on
Direct
4.5
Knowledge)
(DOL)
Starting)
In
the
shown
circuit
example
in
4.7,
Figure
.
press
.
on overload, the OCR-F1 trips out the NC
-F1
should
contact 95-96 (to start motor
again,
be reset by hand after the internal heater's
the
circuit
.
.
Manual
generator as long
is not greater than
dip
voltage
run-up period. For large motor
the supply
of motor
starter
protector -Q1
-KM1. -KM1
contactor
main
of
closing
surge
contactor 'holds-in'
.
-KM1
Control
.
.
.
contactor
out, motor
drops
circuit
control
transformer)
circuit
breaker
stops.)
13-14
contact
of -KM 1 'latches'
indicator
remote
1
L1
contactor).)
will
cause
an
the
as
-H1
lamp
%
10-15
drives,
within
this
'on')
3 x 380 -
X1
-F2
1
3
2
4
h.r1
-Q1
3
5
Start
Stop
-51
-52
-T1
1
-F3
380v/24
v
3
r'\"f1
r'\"f1
X1.7
4
1
I
2
\037-Eft-KM1
I
,-
4
L_
13
14
-F1
L...r
-KM1
X1.9
X1.8
-F1
A1
-H1
X1
Figure
4.7
- DOL starter
-KM1
A2)
circuit)
the
starting
motors
is the reason why
(eg bow
large
and
fire)))
and stern thrusters, cargogears,ballast
3
L3
to
voltage dip at the
unacceptable
2
L2
large
corresponding
This
contactor
.
extra
by
switch,
as all the other connected
compounded
an increased
motors compensate by demanding
current to maintain their original power output. If
current loading may cause
this sudden
prolonged,
line and generator protection to trip.)
supply
1
-S
limit
is further
(eg 24 V from
after closing -F2 miniature
press start button
auxiliary
available
voltage
remote
eg
of other
supply busbars, with likely malfunctions
flicker
and possible
consumers, eg lighting
drop out
breakers
due to
of unessential consumers' circuit
dip
tripping of undervoltage releases. The voltage
circuit operation
Control
can be made for
control (by pilot switches,
additions
but
DOL switching demands a short duration
the
times
FLC
fixed
current
of
5-7
by
starting
motor impedance and is generally
acceptable
operation
closing
automatic
liquid level switch, pressure switch,
an
etc) and motor reversing (with
follows:)
Power
circuit
Further
and
for this starter circuit is as
sequence
switching
-S2
button
cooling down time).)
motor is directly
switched
onto the
AC
lines
means
of
three-phase
power supply
by
contactor
-KM1. This is a very simple
starting
that is used for the majority
of small
arrangement
sized induction motor drives.)
induction
The
stop
Motors
etc) require a more complicatedstarting
to limit the size of starting
current
and
and
other
the
consumers.
protect
generator supply
a reduced voltage at startup.)
This
means
applying
pumps,
Power
method
.
Reduced
4.6
Starting)
Voltage
During
the
current
can be limited
either by
'soft'
and
starting
starting
a motor
is DOL started
a reduced
applying
in
closing contactor
closing -KM2:
star
contactor
.
openingof -KM2:
star
connection
.
closing -KM3: delta contactor
-KM1,-KM3contactors
out,
of
operated
.
starting.)
.
the
with
stator
winding
.
power
.
circuit
the
as
relay,
phase
shown
of pneumatic, electronicand
are available from manufacturers.)
circuit
control
transformer)
circuit
breaker)
time
-S
available
(eg 24 V from
after closing -F2 miniature
1 to
close -KM 1 ; -KM1
-KM3
relay -KT1 energises and begins to
preset time delay
-KT1
time
are
windings
A variety
4.8.
Figure
solid
.
controlled
contactors
in
.
time
state
for this starter
sequence
elapsed,
delay
close
21-22
closingof -KM3 by -KT1 (NO contacts 15-18
contacts
21-22 open
close);-KM3 interlocking
stop by S2 button or OCR trip F1: -KM1, -KM3
21-22 close.)
relay
5-9 secondtime
circuit:)
-KM3 interlocking contacts
-KT1
gap
is usually
depending
set for a
size of
on the
motor.)
-F2
tl
-51
\",
-F3)
5v-'F\037T1
-Q1)
4)
Lj124V
-F1)
1
3
mS)
S)
-KM1)
-KM2)
2
4
6)
2
4
6)
-KT1)
-F1)
X2.2)))
Figure
4.8 - Star-delta
motor starter diagram)
de-energises
15-16 open); -KM2 interlocking
contacts
de-energises;
relays
-KM2
count
-KT1
time
switching
voltage
press start button
Note:
The
stops.)
operation
Control
(NC
automatically switchedusing
by a timing
motor
drop
by
way.)
motors,
opens
of
down
starters for small motors may be
by a manual changeover switch.For
large
contactor
neutral
-KM1:
of
contacts
Star-delta
-Q1
of fused-isolator
closing
Control
star connected, it will only take one third of the
it would
take if the windings
starting current that
current
of a
were delta connected. The starting
motor that is designed
to run delta connected can
be reduced this
operation
holds in; -KM2 closes interlocking
(-KM2 NC contacts 21-22open)
Star-delta
If
81)
starting
some
additional
supply voltage or by inserting
circuit impedance. The mostcommonarrangement
is to apply reduced voltage, which is sub-divided
into
the
methods
of star-delta switching, autotransformer
Manual
.
.
.
the size of motor
period,
run-up
circuit
Starters
and
-KM1)
15)
Marine Electrical
Practical
82
Knowledge)
This means
interlocking contacts of -KM2
are the
Why
-KM3
the
that
from the motor
output
power
is the same when the motor is star connected as
when the motor
so the power
is delta
connected,
must
be
the
same when
inputs and line currents
QUESTION
and
necessary?)
connection.)
in either
running
ANSWER)
This is to prevent
a full short-circuit
fault across
the supplylines during
the
from star
changeover
to delta.)
has
of starting, when the supply
on and the motor has not yet
instant
the
At
switched
been
to rotate, there is no mechanicaloutput
motor The only factors that
determine
taken
the
are the supply voltage (V) and
of the motor phase windings
(ZpH).)
impedance
Compare
the
to
current when star connected
when delta connected, as in
the starting
current
starting
4.9.)
Figure
are equal
connection.)
a star
in
This will
current
motor
the
by
cause
tripped
may occur
malfunction
This
L3
L2)
L2)
the delta contactorfrom
must
4.9 - Star-delta
Figure
line
a very
dip that
voltage
VLI
==
==
3)
affects
every
One way
current of a delta
starting
can
be reduced
to one third
if
full
is also
an
reduced
induction
motor is running
electrical energy input
converts
output. The input
energy
the load on the motor
An
induction
connected
both
cases
motor
current
on
to
load,
load on the system.
limit the starting surge
the
initial
mechanical
is determined
the
speed,
has
reduced
to
supplied
voltage
a transformer.
using
accelerated
up to almost
voltage is replaced by
the
in operation
the
during
starting
period. For induction motor starting,
the
autotransformer
is a three-phase unit and,
of expense,
because
this method is only used with
motor
drives, eg electriccargopumps.)
large
short
by
shaft.)
will
reduce
transformer and it is only
it
at the same speed
as when it is delta
because the flux speed
is the same
(being set by the supply
frequency).)
when it is star
supply
a severe
voltage. The transformer used in this
is not the usual type, with
starter
separate
primary
and secondary
windings, but is an autotransformer
that uses only one winding
for both
input and
This
is
output.
arrangement cheaper,smaller
than
an equivalent double wound
and
lighter
problem.)
When
the
causes
full mains
is star
motor
torque
to
Then, when the motor
connected for starting. The shaft
to one third, which reduces
the shaft acceleration and increases the run-up
time
for the drive, although this is not usually a
the
will
the motor is to step it down
the
connected motor
run-up period will
2
'}{
This shows that
a long
with
high current surge from
current.)
/J3xz
.J3 x
IL(I!.)
and
starting
Reduced voltagestarting
ratio of: IL(y)
closing.)
for a few seconds. This
generator
connections)
interlock
mechanical
connections.)
Starting a large motor
demand
a
overcurrent protection, the overcurrent
be fitted in the phase
connections
correct
Autotransformer
Delta configuration)
timing
prevents
relays
Star configuration)
control
the
is not completed or the star contactor
not in the
L3
if
sequence
For
Vl)
eventual
by the overcurrent relay.
Rememberthat the motor copper losses are
produced by the FR heating effect, so the motor
will run (-V3)2 == 3 times
hotter if left to run in the
star connection
when designed for delta running.
L1)
Vl)
'and
over.heating
unless
burnout
remains closedwhile
L1)
(for the line
in delta
voltage of 440 V) but is run as star connected, and
will be
on full load, then each stator phase winding
an
overcurrent
of
-v3
times
rated
phase
carrying
current. This is because phase and line currents
started
the
from
the
just
to run
is designed
motor
the
If
run
Figure
connected
connected
in
4.10
shows that the supply voltage
across
the complete winding
motor is connected to the reduced voltage
A number
of tappings are usually
available
is
and
the
tapping.
on)))
Motors
QUESTION)
current surge in open
when going from the start to the
the
causes
What
large
starters
transition
condition?)
run
generate a back emf
against
the
When
the
voltage when they are running.
is
removed
from
a
induction
motor,
running
supply
the magnetic field does not immediately
collapse.)
transformer
the
winding, giving
from about 500/0to 80%
ranging
of
output
points
to
give
0
current
demand
As with
the
use
the
60%
of 440
== 264
star-delta
what
is called
cycle.
open
a
V.)
the autotransformer
starter,
starting
the closedtransition
sequence
an
an open transition)
from the supply during
the
Most autotransformer starters used
disconnected
switching
provide
sequence
between
method.)
or a closed transition
switching
the start and run conditions.
In
to
transition, the reduced voltage is supplied
at start, then disconnected and the full
to the motor.)
voltage
rapidly reconnected
motor
the
supply
is that a
current
can
flow
after
the
large
enough
surge
transition
from reduced to full voltage.)
The
problem
A typical
Figure
with open transition
starter circuit is shown in
autotransformer
4.11.)
points
Tapping
X% V L
x = N 1 / N 2)
to motor)
X%)
V L supply
N 1 turns)
N2
turns
X% VL)
Tapping points
Star point
______________-1)
Single-phase
Figure 4.10 - Autotransformer
unit)
connections)
the
further
actually
outputs
on
An
at
stage, causing
dip and
voltage
so affecting other consumers. Closedtransition
starters
overcome
this because the motor is never
mains
a set
50k and 65%),
may
of
usually has a few tapping
of reduced voltages (eg 40%,
which helps to match the motor
to the supply capability.)
autotransformer
The
voltage
For example,a 60% tap
supplied at 440 V would
supply voltage.
autotransformer
voltage
The motor begins to slow down but still generates
an emf. When
in open transition,
reconnected
the supply voltage and motor
emf
are not
is similar to
necessarily in phase
(the condition
changeover
supply
83)
Starters
synchronising a generator onto the busbars).
additional current surge is, therefore,likely
ANSWER)
All motors
and
Three-phase
unit)))
Marine Electrical
84
Practical
The
switching
Knowledge)
for this starter circuit is as
sequence
.
press start
operation
of fused-isolator
closing
\302\267 Manual
\302\267
\302\267
\302\267
.
of transformer
connection
star
-KM1:
closing
of -KM3:
motor supply via transformer
of -KM1:
star connection opens
direct
supply to motor
closingof -KM2:
(Note the electricalinterlock
contactors
\302\267-KM2
drop
of
-F2; control
- T1
from
L2
-K1/55-56
by opened
of
(after time delay has elapsed)
.
KM1-KM2)
(eg 24 V
-KM3
de-energising
-KM1/43-44
by opened
.
closing
contact
-KM1/21-22
.
energising -KM2 by
closed
K1/67-68
.
interlocking of -KM1 by
.
de-energising
interlocking
circuit breaker
available
voltage
de-energising -KM1
OCR trip
))
-KM2/21-22
of -KM2 by
stop
button
-S2
or
(-F1).)
3 x 380 -
1
2
L1
L3
circuit
top mounted
with
module
by -KM1/21-22
of -KM2
interlocking
.
out, motor stops.)
of miniature
closing
relay
time
of -KM3 via closed -KM1/43-44
energising
.
Control circuit operation
\302\267 Manual
control
pneumatic On-delay
-Q1
closing
opening
energising-K1
.
circuit
Power
-KM1, which
to energise
S1
button
in by -KM1/13-14
holds
follows:)
3
X1
1
3
5
2
4
6
1
-F2
..Fv-
3
-
-Q1
-F1 L.J
-52 \n
1
3
5
2
4
6
3
-KM3
-KM2
-51
13
-K1
E4)
67)
-K1)
43
-KM1)
1
-KM1
-F1)
3
5
\\--\\-\\
-KM3)
-K1)
-KM1)
LLj6)
X2.2)
Figure
'Soft'
4.11
- Autotransformer
motor starter)
each
starting
This method of supplying a gradually
increasing
voltage during startup generally refers to
efficient
electronic
switching technique.)
AC
A
basic
method,
shown
back to
back
supply
lines which
connected
in
Figure
thyristors
are gated to
AC
a reduced
an
is to use
or triacs in the
4.12,
delay
turn-on
within)
half cycle.
average
This delayed switching
applies
AC voltage to the motor.)
The applied motor voltage is gradually
ramped
the
full
up by the starter software program until
level is 'reached. To achieve
maximum
voltage
the electronic switching circuit can now
efficiency,
be bypassed
for normal running.)))
and
Motors
soft
starter
to become
adapted
may be further
a voltage controller over the motor
load
operating
In
this
of
efficient
range.
type
energy manager
A
application, the controller monitors
factor,
which
measure
full
voltage,
and
load
light
is a
motor
the
power
of the motor loading.On
the power factor is low
so the controller reduces the motor
85)
that
this type of soft-start/energy manager
IS
a speed
controller.
To electrically change
the speed of an induction
motor it is necessary
to vary the applied frequency.Motor
speed
\037ote
not
are outlined in
methods
control
Section
4.7.)
which
voltage,
current while improving power factor
reduces
Starters
and
efficiency.)
QUESTION)
and compare the likely
Estimate
surges
for a motor that
when
started:)
(a)
DOL
takes
starting
200
A star-delta
(c)
The autotransformer method reduces the
current
A on full
starter reduces the initial
to one-third of the equivalent
starting
surge
DOL
ie
to
about 330 A in this case.
value,
(b)
load
initial
X == t
(b) Star Delta
(c)
.
applng
In this
with a 500/0tapping.)
Autotransformer
to (X)2x I DOL where
surge
starting
point.
x == 0.5,
example,
level is 0.52 x 1000
== 250
so the
surge current
A.)
ANSWER
(a)
When
DOL,
starting
is about
the
initial
5 x FLC, ie 1000A.)
surge
current
Soft starter)
Supply voltage
to starter)
._ ___________
_____
/ -- \"
/ ,,-- \"
3 - supply
Motor
:
\037
\037
:
i
L)
Start
& stop commands)
AC voltage controlby delayed
switching on both half-cycles)
4.12
/
\\
- 'Soft'
starter block diagram)
;-
_---l\037---'t\\--------,7-- '
=:- - ---- I
--
Rising RMS voltage --f-=-==-:.l\\; \\
eg 440 V, 60 Hz)
Figure
voltage
\\
\\
' ...- \"I
ri
Y
\\-\\
\\
\\
\"...-)))
Marine Electrical
Practical
86
4.7
Knowledge)
rotor induction
The standardcage rotor AC induction motor
its
over
operates as an almost constantspeeddrive
load range. This feature is satisfactory
for most
of
the ship's auxiliary
such
services,
as those
forms
main
available:
\302\267
or
speeds,
motors to give
eg 2-speed forced-
fans
and
3-speed
winches
for induction
variable
continuously
using variable
the
60
are
direction
from the winch
operated
One
control
achieved
contactors
reversing
pedestal.)
of an
Remember
that to reverse the rotation
motor it is necessary
to switch over
induction
stator
the
winding.)
in
An alternate method, giving
two
fixed speeds
a 2: 1 ratio from a cage rotor
induction
is
motor,
that
has centre-tap
to use a single stator winding
connections
available on each phase.This method
uses
a starter with
a set of contactors
to switch the
phase windings into
motor is arranged to
power
create
fields.Estimate
rotor
slips
supply is at a frequencyof
At high
speed
n s == 6012
but
rotor
n R == 95%
either
star
single
(low speed))
== 30
p == 2),
(4-pole,
revls
or 1800 rpm
runs at
x 12/100
== 28.5
or 1710
revls
rpm.
Hz.)
At
ns
but
low
rotor
L1)
W3)
==
L2)
L2)
4.13
- Star-double
speed))
star connections)
revls
or 900
rpm
==
revls
14.25
or 855 rpm.)
L1)
L3)
(low
15
runs at
x 15/100
L3)
Star
p == 4),
(8-poles,
speed
== 6014
n R == 95%
Figure
windings.
ANSWER
and 8-pole stator magnetic
4-pole
the
rated
speeds
assuming that the
and
by 5\302\2601o
stator
three
Speed control and drive
and
by a set of switching
frequency.)
induction
wound
dual
winch motor can be
change
having
poles.)
stator winding
gives a low speed,
(usually
24-pole)
to give medium
while the other is dual wound
outputs.)
speed (8-pole) and high speed
(4-pole)
control, eg smooth
electric ship propulsion
QUESTION)
A
pole
3-speed
by
speed
and
of winches
control
of magnetic
two of the supplylines to
fixed
draught
number
change/control are
more
Pole-changing
two
\302\267
of speed
each
different
arranged
Variable speed control
is necessary
for cranes,
winches, windlass, capstans, forced
fans,
draught
etc. A ship's electric propulsion with electronic
speed
control may use DC motors or AC induction
motors
for low/medium power applications. Largepower
electric
propulsion,
eg for a passenger cruise ship,
will use AC synchronous
motors (see Chapter8).)
Two
winding,
A
supplying
fans and circulating pumps.)
to ventilation
power
can be obtainedfrom a cage
motor by using a dual wound stator
winding
being designed to create a
set speeds
Fixed
Control)
Speed
Double
Star
(high
speed))))
Motors and Starters
or
double-star
stator
(high
speed).
are
shown
windings
The supply linesto the
in
Figure
4.13.)
additional
beneath
.
Electrohydraulic
.
wound
.
Where continuously
be combined with
acceleration,
variable
high
including
control of induction
Ward-Leonard DC motor
variable
drive
The
induction or synchronous
frequency
control.)
motor
drive, often used for deck
a relatively simpleelectrical
section.This is a constant single speed induction
motor supplied from a DOL or star-delta starter.
The
electrohydraulic
control, has
crane
The motor
runs
to maintain
continuously
pressure to the variable
hydraulic
speed
problem
DC
power
AC
electrical
A
torque
inching
control
4.15.
drives
supplies
output
for lifts, cranes
Ward-Leonard
drive,
method
Figure
oil
or more DC motors.The generator
one
is controlled
voltage
by adjusting its small
via the speed regulator. The
is directly controlled by the
current
speed
DC motor
speed
generator
voltage.)
of
the value
Increasing
decreases
rotor
the
reducing
the
a high
starting
starting
of external resistance
This has the benefits of
speed.
current surge while providing
torque.)
The wound rotor arrangementis more expensive
than
an equivalent
cage rotor machine. It requires
more
maintenance
on account of the slip rings
resistor bank, which may require)
and
the external
and winches
as shown in
Here, a constant speed induction
a DC generator which, in turn,
rotor induction
control is provided by the
motor. The rotor has a
three-phase
winding (similar to its stator
winding)
mounted
on
which is connected to three slip rings
4.14.
An external
the shaft, as shown in Figure
three-phase resistor bank is connectedto brushes
motor
start
on the rotor slip rings. During
up, a
set of large sizecontactorsvaries
the
amount
of
circuit.)
resistance added to the rotor
wound
and
to consider
system?)
in the
motor
motors.)
is
is: where does the necessary
come from on a ship with
an
supply
traditional
is found
excitation
A crude form
has to
smooth
regenerative
braking,
necessary
the merits of a DC motor drive. Speed and torque
control
of a DC motor requires only
the
variation
of
armature voltage and field current.)
drive
rotor resistance
speed
and
it
motors
.
the
from
extraction
variable speed range of motor
more complication and expense
than
that
to obtain a couple of set speeds.
required
Various methods are available, including:
A continuously
control
involves
(eg forced cooling by a
the bank and compulsoryair
bow thruster room).)
facilities
cooling
situated
fan
The motor generator (M-G)set requiresspaceand
maintenance.
An alternative
is to replace the rotary
M-G
set with a static electronic thyristor
controller,
which
is supplied with
constant
AC voltage
but
delivers a variable
DC output
to
the
drive
voltage
motor, as shown in Figure
excellent
limited
4.16.)
the Ward-Leonard
Although
scheme providesan
drive, practical commutators are
750 V DC maximum, which
also
power
about
to
limits the upper power range. The commutators
on the DC machinesalsodemand
an increased
maintenance
requirement.)
To eliminate these problemsmeansreturning
to
the simplicity
of the cage rotor
induction
motor)
Wound rotor construction
I)
.3t)
rings
assembly)
Slip
\037 '\\
\":,','
'\\
. 4'4\037)
'. .)
-.. .)
;r\037)
Three-phase
rotor resistors'
bank)
Figure
4.14
- Wound
rotor construction)
: ,:.
1 .\037......,.) :;. :&,. -..\"', ..,)
-,)
-,-. .\037.
. . ....\037-
..)
87)
--- i,'
...)
. - .,
.....- .:.\037'::::'.
\037
:')
.
\",f
.,..,....,..,\"
..;.; \037)
.\037)
, ,
'.
';\",
'))
\"'\"
'i\037;:-':\"
L)
i \037:..
.-:)
t .......\037.
J; ,\".l
! \037.
'
.. .....,
-\037.
.
...I
\037
..)
/ . :. , \037
...... \
\"\"!-)
,'-)))
Marine Electrical Knowledge)
Practical
88
+
\037
Speed
Field
,-
control
rectifier
*
M
.
3-)
.J.
J.)
G
M)
r,)
\\../)
M-G set)
3 - supply)
- Ward-Leonard
4.15
Figure
- motor)
3
speed
,.)
,.)
DC
Load shaft)
DC motor)
generator)
method)
control
+)
-f*-)
Field
rectifier)
+)
,)
M)
\037)
3 - supply)
\\)
AC/DC
\037)
Speed
Load
thyristor
control)
shaft)
controller)
DC motor)
Figure 4.16 - Electronic
However,
the
variable
speed
for a DC motor)
control
only way to achieve a continuously
output by electrical control is to
electronic
to the motor. A static
frequency
transistor
or thyristor
(high
power)
controller
can be used to
frequency
output
to
shown
in Figure
the
vary
as
motor,
In
an
supply
electronic
the fixed
AC
generate
control
directly
a variable
the speed of the
such
4.17.)
variable
speed drive (VSD),
is rectified and smoothed by
input
to a steady DC link voltage
(about
600 V DC from a 440 V rms AC supply).
The
a capacitor
voltage is then
chopped
into
variable
width,
constant level, voltage pulses in the computercontrolled
inverter section using insulatedgate
transistors
This process is called
bipolar
(IGBTs).
or PWM (see Figure 4.18).
pulse width modulation
By varying
the
but)
pulse
widths
is
possible
it
and
polarity
of
to generate
an
over a wide range
averaged sinusoidalAC output
of frequencies. Dueto the smoothing
effect
of
the motor inductance, the motor
currents
appear
to be approximately sinusoidal in shape.
By
the currents in sequence
into the three
stator winding,
a reversible
rotating magnetic
field is produced at a frequencyset by the PWM
directing
DC
the
DC voltage,
modulator.)))
Motors and Starters
. .HJB[p)
Handheld
programmer)
.I
I)
- - - -- --- _.- - ---- - -- -
-- ----------_.- -- -- -.-- _._.-..-- _.- - - - _.- -.- -.,
Variable
.)
electronics)
Control
frequency
AC supply
to motor
three-phase
eg 0.5 Hz - 120Hz)
I)
I)
t)
IGBT)
+)
DC
o
r
o
AC supply
three-phase
eg 3 -- 440
- Electronic
4.17
T
inverter
bridge
\"'
VSD controller)
+
..
IGBT
PWM
-<
input
low frequency
A veraged
voltage
output
Controlled
A veraged
inverter
,
PWM
(one-phase
- PWM
4.18
of shaft torque, acceleration time
few of the many
are
a
operational
braking
that
can
be programmed into the
parameters
The
VSD can
VSD,
usually via a handheld unit.
motor drive to
be closely tuned to the connected
and
features
and protection
control
achieve optimum
load
for the overall drive. Speed regulation
against
made
and
can
be
is
precise
changes
very good
by
the
addition
of feedback
from
a shaft
speed
encoder.)
only shown))
A
of
a complex
process.)
of chopping
it creates
disadvantage
such
a drive
back into
voltage
is that
the
supply
power
large currents with
harmonic
voltages
network. A harmonic
is a distorted sinusoidal
waveform
waveshape.)
covered
The analysis
(not
here) of a distorted
of
sinusoidal
harmonic
revealsa
set
waveshape
the
base
upon
superimposed
(or
voltages
fundamental)
can be easily
controlled,
VSDs, being digitally
networked to other computerdevices,eg
controllers
(PLCs), for the
logic
programmable
overall control
principle
control method)
control
Accurate
high
frequency
..)
bridge
Figure
\037)
Controlled
Bridge
r
DC voltage
3-)
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rectifier
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V, 60 Hz)
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;
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e)
.
Figure
--
--B*-)
o)
Fixed
link
capacitor
frequency.
Harmonic
frequencies
of the
are integer (whole number) multiples
In
an
AC
fundamental
system,
frequency.
even numbered harmonics are conveniently
are multiples
self-cancelling,
as
three-phase
network.
of three in a
This leaves
harmonic)))
89)
Marine Electrical
Practical
90
numbered
of 5, 7, 11, 13,
frequencies
the
Fortunately,
Knowledge)
higher
the harmonic
17, 19,etc.
lower the amplitude of the harmonic
For a
voltage.
5t
60 Hz fundamental
a 5 th harmonic
(1
harmonic),
would
be at a frequency of 300 Hz and a
7th harmonic
would
be at 420 Hz. The amplitude
th
of a 5
harmonic
may be up to about 20% of the
the
while
fundamental
7
th
down
be
will
to about
14% and so on.)
disturbances
caused
voltage
can interfere with
other
connected
to the power system,
installation
acceptable
filters,
rating and length, earthing and bonding
cable
etc, beforefitting
a drive.)
such
and
converters
Very large drives use thyristor
motors, eg for ship's electric
synchronous
in Chapter 8.)
as outlined
propulsion,
harmonic
Such
by
Be guided by the manufacturer's
notes regarding the need for
number, the
current
switching
equipment
for example,
in,
resulting
breakdown due to
the lighting
and
progressive
and
Minimising harmonic disturbance involves
good
circuit
of harmonic
filters
design and the fitting
filter is a
adjacent to the VSD drive. A harmonic
combination of inductanceand
tuned to absorb the unwanted
circuits
The
circuits
control
in Figure 4.19 show typical motor
on LV and HV supplies.)
instrumentation/
circuits.)
control
Protection)
insulation
spikes,
voltage
flickering of
malfunction
of low current devices
high
such as electronic
computers
Motor
4.8
units
capacitance
frequencies.)
In the
HV motor protection scheme, the backup
fuses
are
releases
tension
trigger
the trigger type. This type of fuse
held in
a trigger actuated by a spring
the
until the element
melts. When
released,
fuse
or
to
indicate
a
blown
be
used
to
may
or contactor. Trigger fuses are
a single phasing
against
the motor is definitely tripped out
so that
a single fuse blows.)
trip
a circuit
an
additional
fault,
when
HVeg
breaker
protection
3 x 6,6kV-)
-
LV 3 x 380
1
L1
VT
2
L2
3
L3
6600/110 V)
Isolating plug
& socket)
X1)
uv)
Trigger
relay)
5)
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Motor starter
-Q1
protector
r-Ef3-I
with
r-
..r.ri\037.,
Contactor)
Lockout
trip/reset
LO
and
thermal
magnetic releases)
L_)
Under voltage
fuses)
relay)
Isolatmg plug
& socket)
)
Alarms)
Contactor)
-KM1)
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Thermal
overload relay
-F1)
OCIT
CTs
DIFF
eg 500/5 A)
EF)
Combined
(OCR))
motor relay with:
overcurrent inverse
X1)
time
differential (single-phasing)
earth
HV motor with
L V motor)
combined
protection
Figure
4.19
- LV and
HV
motor
protection
scheme)
relay)))
fault)
To protect an electricmotor
be prevented
it must
If
If the
Remember,
temperature of the insulation
its working life by
reduce
The
half.)
the
If
windings.
the maximum set value
for
contactor is tripped to
stop
exceeds
temperature
the motor
the
insulation, its
and allow it to
motor
down.)
.
Thermocouple
.
resistance
.
thermistor.)
and it may
interrupt the fault
short-circuit current will
of
that
are
Thermistors
more
characteristic
closely
than the other types.
of semiconductor
embedded
upon the insulation
a motor
small
pellets
of
material that are
manufacture.
all three-phase stator windings during
When
a thermistor gets hot its resistance changes
so that
connected
are
They
dramatically.
indirectly
the
in
electronic,thermal
or
current
the full
five times
capable
safely.)
of
tripping
severe
before
this
stalled.
motor, which
current.
stalled
current
This is the
is the
possible
load
the
tripping
4.20,
of the
so
coordinated
as
characteristics,
OCR and fuses/circuit
that
the contactor
that the motor fuses are not
rated current but for their inverse
emphasised
for their
(I/t) characteristic. This means that
rating of fuses used to protecta motor
to have any direct relationship to
not appear
FLC rating of the motor.)
the
current
will
the
QUESTION
value of current shouldthe OCR
At what
be
set?)
ANSWER)
To protect a modern continuous
maximum
rating
(CMR) motor, the thermal OCR should be set
at the
full load current (FLC) rating
of the motor.
will
within
This will ensure
that tripping
not occur
two hours at 105% FLC. At 120% FLC, tripping
will occur
within two hours.)
Fuses used for backup
have a special time/current
will
be
about
The contactor is
current quickly and
of motor
protection
characteristic.
circuits
They
are generally carrying steady currents well below
DOL
rated capacity to allow for short duration
currents
without
blowing. Consequently,
starting
their
not
they
do
do
protect
protect against normal overloads but
the motor and supply system against a
fault.
short-circuit
of the
The
current
time-delayed
electromagnetic
has
contacts
current.
This method uses
coil, after a pre-set time delay,
overheating can occur.)
starting
be
must
current/time
the
the
overcurrent relays (OCRs) in the motor starter.
The system is designed so that if the motor takes
of being
too much current as a result
mechanically
will
the
OCR
overloaded,
trip out the contactor
The largest overcurrent
taken when the motor
at its
occur
fault.)
that
Figure
the
if
monitoring
measuring
by
lines.
supply
will
protection.)
chosen
is usually
Direct thermistor protection
only fitted
FD fans, air
to large motors, eg bow thrusters,
conditioning compressors, etc.)
flowing
a short-circuit
breakerare
temperature
gets too high the starter
will
be tripped,
contactor
by an electronic protection
to stop
the motor.)
relay,
temperature
arcing
fail to
instantaneously, thereby protecting the contactor
during
motor
Most motors are protectedby
or
flow.
will
cause
serious
prolonged
to the motor, starter and cable, with an
damage
attendant
risk of an electrical fire. To prevent
this a set of fuses, or a circuit
is fitted
breaker,
upstream of the contactor.This will trip out almost
backup
is probably the most
sensor
thermistor
matches
serious
It
commonas its thermal
the starter
fault current
the
fuses/circuit
trips on thermal overcurrent while
breaker
This
interrupt short-circuit fault currents.
contactor
and fuse arrangement is usually
called
device (RTD)
temperature
motor,
a huge
91)
tries to open under short-circuit
contactor
It is important
sensors
the
in
and
conditions,
shown in
Three main types of direct
temperature
can be used. These are:)
The
can
against
way to protect a motor
is to directly monitor the temperature
best
overheating
motor
of the
cool
maximum
the
10\302\260Cabove
every
recommended
occurs
a short-circuit
the supplycable,then
from getting too hot.)
Starters
Motors
Fuses
backup protection
current
rating
to their
fusing
A typical
have
for motor circuit
designed
continuous
a restricted
'M' rating),
(called
characteristic.)
fuse designation for
which is different
motor
circuits
could
be '32M63', which indicates a continuous rating
of 63 A for the starting period.)))
32 A, but a rating
of
Marine Electrical
Practical
92
Knowledge)
time (t)
Tripping
.
,
,
,
,,
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3)
2)
4)
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.-:)
- tripped by OCR)
Overloads
Note: Inverse/time
4.20 - Motor
Figure
motor
scale)
protection
curves)
.
by a thermal OCR and
motor
exceed
its rated
is protected
backupfuses.
temperature without
being
tripped
drawn
is usually
indicated by
the
motor
above
by
rising
rated value, a number of other
situations
contribute to motor overheating:)
There are three types
used for motor protection:)
.
.
Electronic
thermal
\302\267
a star-delta
.
overheating
electromagnetic.)
of
temperature
.
.
Yes!
current
ambient
overcurrent
relay
high
starter stuck in the
star
connection)
ANSWER)
the
Very
inadequateventilation
by the
protection?)
Although
by fuses)
.
the
Can
Faults - tripped
graphs
have log/log
QU ESTION)
A
Current x FLC)
10
5)
its
can
(OCR)
stoppingand
worn
or
dry
starting
shaft
too
often
bearings.)
The motor windings can only be
these conditions by using
against
protected
direct
thermal
protection.)
OCIT
relays
have largely superseded
as they
have no moving
electromagnetictypes
parts (exceptfor their
very reliable tripping
matched to the motor
is robust, smallerand
electromagnetic
type.)))
output
trip relay)
can
characteristics
circuit.
This
lighter
than
and their
be closely
type of relay
the equivalent
and
Starters
are
operated
Motors
A
block
of such
4.21.)
diagram
in
shown
Figure
The block diagram of
shows that
maximum output
and
temperature,
they have been found to be inadequatefor
continuous
maximum
rated (CMR) motors.)
well below their
OCIT
electronic
the
and time
current
the
sustained overloadsto motorsthat
an electronic OCRis
relay
settings can be
range to match the motor
time. A self-test
of the OCR
with a fixed
be applied
performance can usually
six
FLC.
times
The
setting of, typically,
trippingFLC
and
Most LV motors
are protected
thermal OCRs. Inversetime
a limited
over
adjusted
run-up
time can be measuredand compared
against
manufacturer's
current/time characteristics.)
devices
electromagnetic
Although
can provide
protection
adequate
with time
against
/\037------
-------,
I
OCR)
bimetal
The strips
are heated by
as shown
strips,
the
expensive
OCRs
in
usually
4.22.
Figure
and
current
motor
bend depending on the temperature. If the motor
an overload current, the strips operate
and
the incorporated
open
normally-closed
(NC)
in turn,
contact 95-96which,
trips out the line
the
takes
delays
contactor to stop the motor.)
large,)
I
...
m)
-------------
work with
by less
thermal
t
CT
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t:
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40
filter)
20
Current
o)
1)
setting)
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t
20)
tI
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/)
Test current level
eg 6 x FLC)
\037
Time
setting)
t:
ol.)
(l)
CI)
10)
Test)
20 Second
Detector)
5)
Trip/alarm
output)
Amplifier)
4.21
5 Second
setting)
,----------------------------\037/)
Figure
settmg)
......)
- Electronic
1)
2)
3)
5 6
4
I)
(x FLC)
overcurrent relay and 1ft curves)
Current input
Radiated
Trip
heat
Bimetal
'\\
'\\
'\\
strip
/
/
/
Current input
Heater
----
\0375_r
96\037-
------....
----.
------ .-
Heater
Indirectly
Figure 4.22 - Thermal
circuit
Heating element)
heated)
overload
relay
action (single-phase
is shown))))
Bimetal
strip
Load terminal)
bar)
Marine Electrical
Practical
94
can
tripping current of such a device
a small range. This adjustment
minimum
The
be
over
adjusted
altersthe distancethe
operating the trip
For
the
Knowledge)
have
strips
before
to bend
contact.)
larger motors, the heaters do not
full motor current. They are supplied
from
transformers
(CTs) that proportionally
the motor current so that
smaller
step-down
To
is not so simple with
a delta
motor. Normally, the line current divides
between
two phases
of the motor
situation
connected
heater
phasorally
windings.)
motors must be
induction
connectedto a three-phaseAC
started,
is correctly
OCR
The
may be used.)
correctly,
operate
so the line connected
current.
sensing the winding
If the overcurrent
a
setting is exceeded during
off.)
fault, the motor will be tripped
single-phase
are equal
currents
line
carry
current
components
supply.
Once
even
if one
they may continue to run
The
of
phasing
single
as shown in Figure
4.23,
is usually
caused when one phase out of the three-phase
power supply system is missingfor any reason
(for example, a blown fuse, the contactor's main
contact
fails to close or a bad contact,etc).The
effect
of single phasing is to increase the current
in the
two remaining
lines and cause the motor
to become
very noisy due to the uneven
torque
produced
in the
of the
one
When
lines becomes open circuited,
The table
below shows typical
and phase
currents at various levelsof motor
loading
during
For large HV
a negative
a single-phasing
to
measure
a separate
(NPS)
sequence
amount
the
in
the
motor
in
shown
Condition
(unbalanced)
,,-
% of rated FLC
I
Table
L2
and
I
ok of
rated
FLC
Iw
and
lu
L3
Iv
60
102
62
131
70
130
79
161
100
243
129
4.2 - Typical line and phase current
ffi Single-phase
fault)
L1)
\",
VL)
(\037
M
3-
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,
IL3)
'--
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I
L3
ffi)
L2)
IL2)
Unbalanced
Unbalanced rotor
stator current)
causing
Figure 4.23 - Single-phasingfault)
as
(balanced)
device, called
relay, is used
of unbalance
currents.)
fault,
of line
Single-phasing Fault
Healthy
machines,
phase
values
Figure 4.23.)
rotor.)
due to single phasing
will
be detected
by the protective OCR. The three
thermal
elements
of an OCR are arranged in such
a way that unequal heating of the bimetal
strips
causes a differential movement that operates
the
OCR switch contacts to trip out the motor contactor.)
a
balanced.)
longer
in line current
increase
= O.577/L)
J3
Condition
An
as
current
line
are
the
Now
I
the
condition no longer exists.
three-phase
sets
of line and phase currents
no
balanced
Single phasing,
=
/PH
and can result in motor
bu rnout.)
is just over half
current
phase
the three supply lines becomesdisconnected.
This
is called
motor windings, the phase
connected
star
For
and
torque
shaft vibration)))
values)
185)
Note that
V1-V2 is
in winding
current
the
considerablyhigher
95)
Worse still, if the operator
makes several attempts
to restart the motor,
it will burn out.)
other two
in' the
that
than
Starters
and
Motors
windings.)
condition where the motor
at the
Look
must
single phasing occurs, the line
102 % of the full-load value, but the
in winding V1-V2 is 131% of its full-load
current
will probably not
value. The 102% line current
OCR
and the motor
activate a line connected
of full
when
load
are
currents
remains connected. However,
in
V1-V2
winding
of the
the
local
motor will
quickly
Undervoltage protection is necessaryin a
that supplies motors. If there
system
is a total voltage loss or blackout, all the motors
be disconnected from the supply. This is to
prevent all the motors restarting together, which
in a huge current surge, tripping
would
result
out
the generator
Motors
must
be
restarted
in a
again.
controlled
after
a
failure.)
sequence
supply
must
overheating
in
result
Motors can be protectedagainstthis condition
by
out with
trips
using a differential type relay that
unbalanced currents. In fact, most modern thermal
OCRs for motors have this protection
against
feature.
single phasing incorporated as a normal
4.24.)
action is shown in Figure
A differential
lost.
For large
it
is
phasing
when
occurs
in
incorporatedinto
on
operation
closed,
normal
under
With no ventilation
delay will
result
to run
conditions,
the
on
stationary
and severe
in rapid
Trip
protection
motor, this time
overheating.)
DC
contact
function
OCR
protection
of the
all
functions.)
supply
voltage
not restart
will
becomes
its
until
energised. This will usually
to press the stop/reset button
start sequence.)
available,
coil is
the operator
the
initiating
contactor
require
before
Diff.
trip
95
\037
96
r.
'\\
\\
the
the motor
__n_
._______
UV protection
by an undervoltage release
air circuit breaker (or motor
which incorporates
relay
necessary
95
Bimetal strip
an
electronic
When
to speed.
up
the
motors,
starter protector)separatefrom the
or it may be part of a special motor
unless
light load, the motor keeps on running
If
the
motor
is
the protection
the
contactor.
trips
the
is
it
will
not
restart.
When
contactor
stopped,
current
will take a large starting
the
motor
The OCR is set to
no rotating
but develop
torque.
to flow long enough for the
allowthe starting
current
motor,
HV
covered
be
will
is
motors
spring-loaded motor contactor
drop out when the supply voltage
by the
because will
for LV
protection
(UV)
Undervoltage
provided
function
single
you
attempts,
the cause.)
investigate
distribution
damage.)
If
fails to start after two
a motor
If
60%
is at
\0375
.n___\037_
,e--r:.
\037
I
I
I
I
.
Threebimetals
cold
Three bimetals hot
position)
I
.)
I
Two bimetals hot,
(balanced)
(a))
,
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;
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(b))
Figure
4.24 - (a) Singlephasing
(b) OCRinternal
protection
components
(differential
(top cover
action) and
removed))))
t .)
I
1 cold (differential))
trip
96 PracticalMarine
system
restarted automatically
a blackout.
following
Knowledge)
loads, the restart may be performed
by a sequence restart system.
ensures
that essential services are
For essential
automatically
This
Electrical
on
restoration
Timer
relays
of
startup
in
Motors)
Single-Phase
Low
typically
supplied
Common
types
tools, domestic
for power
motors
power
equipment,refrigerators,
vacuum
at 220
cleaners,
V AC 50/60
shown
circuit,
as
During
the starting
capacitors
create
in
capacitors
4.25.)
period, the two
a large-phase
\302\267
.
Hz.)
motor
induction
shaded-pole
motor
\302\267AC
single-phase
similar
motor.)
commutator
Split-phase
A
motor
induction
to that
motor
induction
has a cage rotor
type. A single
a pulsating
magnetic field
AC
current.
This
single-phase
motor
induction
used
a three-phase
in
stator winding
produces
when energised with
field cannot exert a rotating
paralleled
angle to the'S'
current. As the rotor
runs
up to speed, a
switch cuts out one of the capacitors. The switch
on the rotor shaft or a
may be a centrifugal
type
relay
in the
terminal box. This type of motor gives
and running
with a reasonable
torque
start/run
capacitor
on the
force
cage
in
winding
etc are
are:
Split-phaseinduction
are used
two
Figure
current-operated,time-delay
.
additional
the
winding circuit may be disconnectedand
the
rotor will continue to be pulsed around by the
flux. This is called a capacitorstart
motor,
magnetic
which
is only useful for driving
a very
light load.)
For starting and running,
4.9
to run,
started
has
motor
induction
phase
starters
essential motor circuits are set to initiate
a controlled sequence.)
motor
the
When
of supply
the
in
start/run
Capacitor
rotor.)
motor
good
starting
power factor.
Mostsplit-phasemotors
are
for a 4-pole
arranged
stator winding
at 50 Hz, its synchronous (flux)
so,
will be 25 rev/s or 1500 rpm.
As with all
speed
induction motors, the rotor will slip causing the
shaft speed to be about 24 rev/s or 1440 rpm on
no load. On load, a single-phase induction
motor
will run with greater slip and operate with
less
than a three-phase version.)
efficiency
Shaded-pole
induction motor
low torque machine useful for low power
such as small coolingfans
in electronic
is a
This
drives,
equipment.)
used
a rotational
to produce
One
method
is to
0
at 90
to
employ two stator windings fitted
other with both connected across the same
each
force
split-phase motor. To get the
magnetic field (and therefore
inducea rotating
force
into the rotor), one winding
is electrically
phase shifted by adding
capacitance
in series with
one
of the windings.)
This
supply.
effect
of
is the
a shifting
.
.
.
S
v-
,
./.I
.
.
Figure 4.26 shows how
pole is partially
with
of each stator
side carrying a thick
face
the
one
called a shading ring. The pulsating
AC
into each half of the pole, but is time
in the
delayed
part with the shading ring. This is
dueto an induced current in the ring that opposes
flux change in the shaded
part. To the rotor, this)
wire
copper
flux
divides
Cage rotor
*
.
III
Laminated
steel core
r-T1
I
I
Cage rotor
+ Centrifugalswftch
Excitation
C1
Run
Figure
split,
4.25 - Capacitor-start motor
coil
Shading
C2
Start)
circuit)
Figure
4 26 - Shaded-polemotor
construction)))
ring
Motors
delay appears as a flux shift across the overall pole
face, which drags the rotor with it by the normal
induction motor action. The developedtorque
is small and the machine is not very efficient,
it is an inexpensive
but
drive for very low power
applications.As with all induction motors, the shaft
base speed is fixed
by
50 Hz the maximum
will
loading
speed
the rotor to slip below this value.)
cause
This is a DCseries motor,
The maintenance requirementsfor cage-rotor
induction
motors are very simple:)
.
operate very effectively on an AC
(see Figure 4.27).)
lubricate
,.,
\" .)
.'-.\037\037\"
I
.- ....,,'
:.,
'.....--:,' \"
;
\037 ,\037..
-'
,.\037'
'
- . -,...
- ==.- .\037.
. ,. <\\.\"
\037\037
\". , .-:.... \037 ...)
I'; .'
..
\037\\
'
and exterior are always
dry.)
these
requirements
are met, an induction
service during
give trouble-free
should
its
life.)
QUESTION)
:)
It
'-)
correctly
the interior
both
Provided
motor
long
,
bearings
and
clean
supply
voltage
contact
resistance low)
to
is designed
high and
resistance
insulation
Keep
\302\267 ensure
which
97)
Maintenance)
4.10
.
motor
commutator
AC
supply frequency, so at
is 3000 rpm and shaft
the
and Starters
,
.:'\037';-;.
, ,'''.>!)
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\\)
\037-. _--
\037\"tY'i.\037'
'.)
r .
,)
most common cause of
What
is the
motor
failure?)
induction
ANSWER)
.1
'
:.'
.;...\037
t')
1/)
,I)
4.27 - Commutator motor
Figure
Failure of stator insulation
major problemwith marine
when
particularly
to dampness
is a
motors.)
motors are mostat risk,
they are not used for long
ventilated
Open
construction)
due
periods.)
The
shaft
torque produced is given
by
([J is the flux produced
T == (]) x I, where
For motors installed on the outer decks (eg
by the
connected stator winding
and
I is the
in the rotor. As
armature (and supply)current
CP is produced
by the same current, the torque is
==
T
makes this single-phase
[2, which
essentially
AC motor more powerful
than
induction
types.)
series
At 220 V AC, the shaft speed on light load is
controlled
typically 12-18,000 rpm and is easily
or
electronic
an
additional
series
resistance
an
by
The
falls
with
speed
voltage
regulator.
rapidly
load torque.)
increased
rated
up to
sanders,
drills,
etc.)
The commutator and brush contacts will
some
sparking
in
normal
operation,
cause
which
can
cause radio/television interference,so a high
frequency
th is type
voltage
of motor.)
thrusters,
and ventilation
cargo
cranes,
fans
including
anti-condensation
and
suppressor
is usually
fitted
to
mooring winches
hold ventilation),
heaters should be regularly
that they are actually working
the motor dry. These
are normally
to see
checked
keeping
space heaters, usually 200 V AC, which are
switched off automatically when the motor
starts.)
cleanliness is extremelyimportant.
routine is required to remove
cleaning
harmful
of dust, dirt, grease and oil from
deposits
both inside and outside the motor.
The
cleaning
of the external surface is particularly
important
for totally enclosed
motors that run continuously.
The heat generated in these
motors
is removed
A thick layer of dust
the
external
surface.
through
will
reduce
the heat dissipation
and create very
Internal dust and dirt in open
temperatures.
high
ventilated
motors must be regularly
removed
by
screens
and
blowing or extraction and ventilation
For
all motors,
A regular
This type of motor is used in equipment
a few hundred watts, such as power
jigsaws,
bow
ducts
cleared
out.)))
Marine Electrical
Practical
98
are to be blown out, the air
If motors
absolutely
than
1.75
dry
and
bar.
If
the
the
is higher than
insulation
pressure
the
be
must
used
should not be more
pressure
the dust into
it forces
than
Knowledge)
winding
this,
rather
contaminated motors may
it.)
removing
blowing
other
flying
been dismantled for cleaning
has
motor
a
When
out a motor, remember to cover
up
machines in the area to protect them from
dust.
Suction
blowing
cleaning is better than
When
immersion
total
require
fluid. Broken
of the stator windings in cleaning
or
be repaired
or missing bearing covers must
replaced to prevent grease escaping.)
and overhaul,
be thoroughly inspected. In
can be detected beforethey evolve
it should
faults
this
way,
into
a major
breakdown.)
out.)
Stator
Lookat the
QUESTION)
How often should a motor
be
cleaned?)
ANSWER)
This will
by the local
determined
be
generally
conditionsand the type of ventilation. Only the
external surfaces of totally enclosed
motors
will
require
However,
cleaning.
regular
outside and inside of open
both the
motors
attention.
The inside of a totally
motor
can be cleaned if the motor
ventilated
will
routine
require
enclosed
been dismantled for bearing replacement.
in areas
where considerable
amounts
of airbornedust are expected
(hatch ventilation
stator
for damaged
windings
insulation
of the rotor into
replacement
the stator.
Oiscoloured insulation is an indication
that
the winding
has been overheated. The cause
of overheating
must
be found and corrected before
the
motor
back into service.)
allowing
by careless
caused
Carefully examinethe stator corefor
caused
with the rotor, usually
rubbing
bearing.
Even slight
the stator will
of
rubbing
generate
enough
the
signs
of
by
a worn
rotor against
heat
to destroy the
stator insulation. Replace the bearingsif necessary.)
has
Motors
fans are a good example)will
frequent
require
more
iron
cleaning.)
Contamination
by
have
been
steel core plates that
badly
may cause a local hot spot to be generated
when the motor
is running.
This is because the
Laminated
scored
and
oil
from motor
grease
bearings is often a cause of insulation failure.
The insulation
should
be cleaned
by brushing or
electro
solvent.
spraying with slow-drying
Badly)
will increase
losses
in
the
,)
'v'2
u 1 .-)
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.
3\302\267
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5
1
10
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7
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fy
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MQ
.
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U1
Figure
4.28
- Motor IR test)
I, \\
t C\037
-<)
'(OJ .OJ.L...
..VJ1)
y,)
damaged
area.
After
the motor has been put back into service with new
temperature.
bearings, check the motor
running
the motor
After a short period of service,
dismantle
and check for discolouration
at the core damage,
If you
which will indicate
local heating.
suspect
core
will need to be)
core hot spots then the motor
20')
-O-\\t\037)
,,'SULATION
TESTER)
NITEsr'\"
egohmmeter
\037
\037
C T111250
V
, ; .:\037\037:CCHII
CaLNr.5778
.6@ (E!
i
01 ED
T09'dIage
0
R. IIarI(&I
. U)
R;\037)))
0
8 G
0 O
and
Motors
dismantled for the laminations to be
re-insulated (which is a shore job).)
resistance
insulation
The
of
indication
moisture
an
phase
earth
failure
short-circuited
fault,
to phase
from view. The best policy
hidden
areas
as part
the bearings
reading is the best
in the motor windings.
Breakdownsdue to insulation
in
and
cleaned
result
usually
turns
a
in
or
phase,
99)
renew
is to
maintenance
a planned
of
Starters
programme. If this is not possible because of cost
or a shortageof replacements,
then
bearings
should be removed, cleaned and inspected
for
signs of damage before a decisionto refit or renew
is taken.)
faults.)
Before opening up
a bearing,
make sure that
the
around the housing is cleanand dry.
recommend
that bearings should
be removedfrom the shaft as seldom as possible,
but
and inspection
is best done with the
cleaning
off the shaft. If the correct
size of wedges
bearing
area
complete
Manufacturers
QUESTION)
How
do you check the insulation
resistance
on an induction motor?)
phases
between
or pullersis used, removal
should
not cause
any
damage. Bearings should be cleanedby immersion
in a solvent, such as clean white
or clean
spirit
ANSWER)
Largermotors
six terminal, which
usually
six ends of the stator windings
are
means that
all
are brought
out
to the
terminal
between the terminals are used to star or delta
the motor. Disconnectthe supply
leads
and remove
the links. Test between phases
with
an insulation
resistance
tester, as shown in
inside
the
is available
can arise on small,threeterminal
the star or delta connectionis made
motor.
Only one end of each winding
at the terminal block. Phase to phase
cannot
resistance
insulation
three
Once
terminal
asking
be checked.
If
a
motor is to be rewound,
consider
to convert it to a six terminal
the repairer
arrangement.)
motors
fitted with ball and/or roller
are
robust
and reliable
bearings
little trouble
very
provided they are
clean and lubricated
kept
absolutely
are
bearings.These
and should give
properly fitted,
correctly.)
Many
in
hand
one
and
slowly turn
the
race.
outer
Any
sticking or unevenness in the rotation requires a
re-wash of the bearing and rotation
in the cleaning
If the sticking
fluid.
persists, the bearing must be
with visible signs of
rejected.Similarly,
bearings
engineers
argue
that
if
be operating correctly it should
vibration
also
be replaced.)
When
shaft
fitting
a bearing
and apply a thin
bearing squareon
force the
(pipe),
The drift should
a bearing
seems
to
be tampered
not
.with.)
Portable
the
must be lightly
oiled.
bearing
Any
of metal particles, such as brass,indicate
wear
and the bearing must be replaced. If
cage
there
is no evidence
of metal particles,carefully
examine
the raceways
and rolling
elements
for
the
inner
race
signs of wear or damage. Hold
dry,
corrosion, overheating or damage, and those with
noticeable degree of roughness in rotation,
should
Bearings
Induction
skidding can damage the rolling
raceways.)
traces
where
motors
and
elements
of clean, dry
should not be spun by
Bearings
because
air jet
the
4.28.)
A problem
air.
compressed
connect
Figure
dried in a jet
paraffin, then thoroughly
block. Links
detection
results,
sampled
periodicallyand analysed, can be a very useful way
to recognise the onset of a bearing
failure. Bearing
or
temperature, eg using embeddeddetectors
with
infrared (IR) spot checks, is another
portable
indicator
of the general
health of a shaft
bearing.)
of
easy to predict (with any degree
that have
certainty) the unexpired life of bearings
already run for some time. Also, inspection may not
It is not
show damage to raceways
and
rolling
elements
in)
the
to a shaft, first clean
the
of light oil. Set the
shaft
and, with a tubular
film
bearing against the shaft
bear on the inner race as
drift
shoulder.
close
to the shaft as possible.Large
can be
bearings
heated for 10-15 minutes in clean
mineral
oil up
to 80\302\260Cto facilitate
fitting. Lubricate the bearings
with
the
correct
of grease
type and quantity
as recommended
the
Fill the
manufacturer.
by
bearing about one third
causes
Overgreasing
results
in
heating,
one
to
churning
full
with
grease.
and
friction,
which
of the
oxidation
possible leakagethrough
half
the
grease and
seals.)
On account of the high
ambient
and
temperature
excessive vibration that many
marine
motors
endure, grease life can be short and fresh grease
should be applied at regular intervals.
Unless
the
hole
to allow excess)))
bearing
housing has a vent
a
100 PracticalMarine
Electrical
to escape,
grease
it
Knowledge)
be
will
to clean out
necessary
the bearinghousingbefore chargingit with fresh
Because of the vibration
on ships,
grease.
bearings
can be damaged when the motor
is not running.)
The
starter and other control
motor
the
maintain
equipment
inspected to check and
be regularly
should
items:)
following
Enclosure
The shafts of stationary
be
should
motors
periodically rotated a quarter turn to
vibration damage to the bearings.)
Check for accumulations of dirt and
corroded parts must be cleanedand
minimise
where
motors tends
cage
to
involve
the
stator
mainly
windings and bearings.
rotors
little
or
no special care in
Cage
require
normal
service.
for
Inspect
signs of damage and
rotor
of
in the
overheating
cage
induction
its laminated
and
winding
steel core. Make sure that all core ventilating
ducts are clean and clear. If an internal
fan is
it must
be
in
condition
good
it is
if
to provide
adequate cooling.)
high
the
steering
flat and
of overheating
and loose
vibration
Maintenance
repainted.
its earth
and
bolts
fixing
bonding connection, particularly
is present, eg in the
Rotor
fitted
the starter
Examine
rust. Any
forecastle.)
and relays
Contactors
for
Check
signs
any
connections.
Remove
from insulating
breakdown
magnet
by
surface
armature
of
tracking.
contactors
or
rust
prevent
grease
voltage
Ensure that the
to prevent
components
Remove any dirt
may
any
and
dust
moves
freely.
from magnet
faces that
correct
closing.)
excessive
pitting
QUESTION)
has been flooded
with
seawater
and its insulation resistance is
to zero
MO. What is the procedurefor
down
the motor back into
service?)
putting
A
motor
induction
cage-rotor
ANSWER)
main problem is to restore
resistance of the stator winding
The
This is achieved in three
the
insulation
to
a high
value.
stages:)
Contacts
Examine for
and
roughness
to burning. Copper contacts may be smoothed
acts
as
using a fine file. Copper oxide,which
resistance, can be removed
using
glasspaper.)
due
a high
Do not file silver alloy contactsor removesilver
A thin
smear
as it acts as a good
conductor.
oxide
of electrical contact lubrication helps to prolong
have
to be
contacts
the life of all contacts. When
replaced, always replace both
.
Cleaning
.
contacts
re-varnishing.)
Salt contamination can be removedby washing
fresh hot water. Any grease
or oil on the
windings has to be removed
using a degreasant
with
The
pairs.
should
three-phases
drying
.
in
fixed
and moving
entire set of contacts in
be replaced.)
Check contact spring pressureand compare
contact
sets for equal pressure. Examine
powerand control fuse contacts for signs of
and
lubricate
the contact blades on
overheating
adjacent
fuse holders.)
liquid.)
Connections
the
Dry
heaters
stator
windings
or lamps with
current
special
injection
load
escape.)
injection
transformer.
level
well
Be sure to keep
below the motor's
rating.)
With the windings clean
IR test remains high
over
a couple of coats
insulating
to
the windings can be heated by
from a welding set or from
a
the injectedcurrent
full
electric
power
of ventilation
plenty
allow the dampness to
Alternatively,
low
with
varnish.)
of good
and dry,
a few
and
if the
hours, apply
quality air-drying
Examine
all power
and control connectionsfor
signs of overheating.
tightness
leads
for fraying and brittleness.)
and
Overcurrent
relays
Check
settings.
for
proper
A thorough
performance test may be carried
incorporated test buttons.)
Control
Check flexible
OCR
out by using
the
operation
a
Observe the sequence of operation
during
of the motor.
normal start up, control and shutdown
Remember to check that the emergency
stop
buttons are operational.)))
Five
Chapter
Services)
Electrical
Ancillary
5.1 Navigation and Signal
a typical
rating of 65 W,
power
ratings are also permitted
40 W
60 Wand
but
cases.)
in some
Lights)
Due to the essential safety
position and visible range of
on board ships is prescribedby
the
Maritime Organization
(IMO) in the
'International
for Preventing Collisions
Regulations
at Sea' (COLREGs).In the UK, the National
for maintaining
marine safety standards is
Authority
The
number,
lights
International
navigation
the MCA
and
(Maritime
The most common arrangementis to have
specially-designed
to as
referred
port,
starboard
Two
anchor
bridge. The side lights
for
and aft,
fitted forward
from the navigation
while
starboard,
also
red
(-)
Aft
()
Morse light)
mast
Each
light
from
a
fitting.)
supplied,
switched,
fused
a navigation
light panel
in
The electric
V AC, with
main
Anchor
Figure
light
light
5.1 - Ship
Aft)
(\037)
\\)
(\037)
The
navigation lights
arrangement)))
switchboard.)
light panel has indicator LEDs
alarm to warn of any lamp or
failure.
Each lamp circuit is monitored
navigation
audible
an
and
circuit
lamp
by the electroniccircuit
basic
Figure
navigation
5.2.)
for
the
light control
lamp
current.
A
panel is shown in
headlight
Anchor
light)
\302\260)
\302\2601
Side
main
standby powersupply.)
Steering
<.e.e
the
power is usually
provided
supply fed from the
(J
Stern
to have
or two lamps and
position,
a dual
is separately
and monitored
on the
of more than
masthead light(s) must be visible
from
a range
of
6 nautical milesand the other navigation
from
lights
3 nautical
miles.
To achieve
such visibility,
special
filament lamps are used, each with)
incandescent
vessels
each
practice
An alternative or standbypowersupply
is fed from
the emergency switchboard. A changeover
switch
on the navigation light
selects
the main or
panel
may
panel
light
at
lampholderswithin
for
requirement
is common
it
essential servicessectionof the
for port and green
the other lights
are
white.
For
50 metres
in length, the
are
two fittings
at 220
five
navigation
running lights
foremast, mainmast (or aftmast),
and stern (see Figure 5.1).)
lights,
be switched
lights,
wheelhouse.
Agency).)
Coastguard
navigation
Iight(s))
light Fwd
Fwd mast headlight)
Marine Electrical Knowledge)
Practical
102
.0)
2
3
4
Masthead
tightAft
Port
Sidelight
StarboaRl
Sidelight
0
0
0
1
Masthead
l\037htFwd
0
1,
I
2
1
I
2
2
5
Steml\037ht
0
2
2
'\".:')
6'
7
8
9
AncI10r
LightFwd
Anchor
Ugh(Aft
MorseUght
Steering
Ught
0
0
0
I
0
I)
1
.
2
.
2
.)
PanelDilnmer
Miri
Figure
Various
5.2 - Navigation
light
lights with
signal
in
shown
that
signal
international and national
Pilotage
requirements,
red,
and white
green
5.2
are
lights
states
relating
switched
regulations.)
health, dangerous
the
signal
Emergency
Lighting)
in
to various
cargo
with these
conditions,etc areall signalled
lights.
White morse code flashing
lights
may also be fitted
on
Powersup\037y
1.Mainsource
2. Elnergency
Source)
panel)
5.3. These
Figure
2)
Max)
colours are arranged on the signal mast, as
combinations
2
o
I
,
2
on
Depending
the
ship's
Classification
and
tonnage, the Safety of Life at Sea (SaLAS)
Convention prescribes requirementsfor emergency
the vessel. Emergency
lighting
throughout
fixtures
must
be marked as such for easy
lighting
identification
(eg with a red disk).)
mast.)
Most
The NUC (Not Under
state is signalled
Command)
mounted
at
using two all-round red lights vertically
least 2 m apart.
These
important
lights are fed from
the
24 V DC emergency supply, but some
ships
NUC
fed
may also have an additional
light-pair
from the 220 V AC emergency
power supply.)
of the
emergency
lighting
is continually
from the ship's emergencyswitchboard
powered
220 V AC. Emergency lights
at the staircases
through
ship's
the
route may
escape
24 V DC battery supply.)))
be supplied from
at
and
the
Electrical
Ancillary
-)
G
W
G
W
I!
\037
I
\037 I
\\.'\\ iI
\\
\037
!i
Ii'\",
',j
24 V)
NUC
220 V)
NUC
24 V)
NUC
220 V)
,! I
\037
------.-.---
7/
R
-
:::
W
II
II
II
R
-\"w
7--r
\037r=\037
,
I
j
!
\037oo
i
\037
Ll
w
rr
:.
!
--Tl-\037----
1
NUC
w\037
\037\037\037l_oR
!
:
1
I
= I-
-Tj-
'\\\037
L
R_
w'--
R
!
\037
103)
Aft Masthead Light)
j
i
i
!
-
Services
:
;
:
I
I,
!
!
I
\037\037)
Top of wheelhouse)
Hue24V)
Hue220V)
I)
i
I
I
STBD)
\\
--I
I
-
\037
I
b
\037)
DDD
I
D
;I[J , _J
I
1 _
if[
I\\
-
l:===-
\037
------------)
\037 .
r
\037I)
Figure
PORT)))
-
5.3 - Signal
lights arrangement)
Electrical Knowledge)
Marine
Practical
104
Mains
supply
eg 220 V AC
Power
--
and
24 V DC
rectifier
unit
battery
--
Junction box
-.\"
\037\037
t
!::J
LED modules
\037
...... -
\"',
j
Extruded
metal channel
house
LED modules)
to
Figure 5.4 - Low
lighting
(LLL))
and emergency
lighting
systems
of electrical power, associated
main
The
location
(sources
transformers,switchboards
central
and
Passenger
lighting
distribution panels) must be arranged so that a
or other incident would not cause the failure
of
both systems,
ie the components of the main and
must
not be located in
emergency lighting
systems
fire
If
rooms.)
same
the
power supply fails, the emergency
must
switch on automatically. Local
system
main
the
lighting
switchesmay
the
be
off the
switch
only where
provided
emergency
is
lighting
the ability
to
in
eg
required,
passenger
must
ships
a special
emergency lighting
routes in the engine
battery-supported
main escape
room and accommodation
along
system
and
at the lifeboat
on
deck.
the
positions
Generally,
illuminate
emergency lights in the accommodation
on
mains
failure.
The
immediately
system's
maintenance-free
battery, usually Ni-Cd (nickel-
cadmium),is continually
trickle-charged
from
the
normal mains supply via a transformer/rectifier
circuit. This battery is then
available
to supply
the lamp via a OCto AC inverter
when
the mains
power is absent.)
This
Where,
accordance
divided
into
main
with
fire zones,
a ship is
SaLAS,
at least two
to be provided for the lighting
of
each
switchboard,
emergency
service.
The
supply
if
this
fire
main
is permanently
in one
supply
power
only
function
light
fittings
the normal
arrangement
supply,
is called an
or UPS,
and it will
for a few hours.The battery-supported
can be simply tested by switching
mains power supplyor, in some
by a test switch on the actual
off
cases,
fitting.)
in
circuits must be routed so that
main fire zone does not
of
the other zones.)
lighting
a fire
power
uninterruptible
circuits
must
have its own power
zone, and each of these
circuit.
One
circuit
can
be
supply
supplied from the
the
with
wheelhouse.)
in
are
ships and RoRo
also be fitted
with
interfere
36 passengers
Passenger
ships carrying more than
are required, by the IMO, to be fitted
with
low
location
to
routes
lighting (LLL) identify
escape
normal emergency lighting
is less
effective
due to the presence of smoke.
An LLL system must
function
for at least
60 minutes after activation
and
it should
indicate a line along the corridorsof an
where
holds must be installed so
Lighting
when
that,
used, there is no overheating
properly
of the
fixtures
or their surroundings, even
lighting
fixtures
in cargo
when the ship is loaded.)
Adequate
escape
is to be provided for
illumination
the
the deck region
arrangements,
where personscomeon board or leave and at the
outboard
transfer
control positionsfor
the
mechanical
pilot hoist.)
route.)
of an
Figure 5.4 shows the main
components
LLL system, where the LEOsare wired
onto
a
circuit
board
within
a
clear
printed
polycarbonate
at each end)))
rectangular tube that has connectors
A
similar
is available
arrangement
using low power
incandescent lamps.)
room
the
When
Periodicinspection
and
is an essential
of all
testing
ships.)
Air
and
Refrigeration
the
basic
will
have
air
a domestic
In
the cooling effort is
to switch
refrigerator,
controlled by using a control thermostat
the compressor on or off.)
principle is common to them all. Each
a refrigerant
evaporator
(cooling unit),
an
and a condenser.)
compressor
The
sealed
hermetically
split-phasetype,
The refrigerant
used
is generally
Freon-R417
R404 or other
units
use
container
R-134a,
(reefer
which
is
classified
as almost
of
types refrigerant),
harmlessto the
ozone
layer
if
into the
it escapes
windings,
separate
start
5.6.)
in Figure
shown
as
motor is the
compressor
two
with
The motor
is accelerated
both
by connecting
start and run phase
to the supply. When
windings
about
reaches
motor
the start winding
is tripped
compressordrives,
in general
use are colourless
Freon refrigerants
and
almost odourless,non-toxic,non-corrosive
an
when
to
non-flammable.
However,
exposed
open flame
and run,
the
atmosphere.)
severe
natural
through the evaporator coilsor by
from a fan blowing
across
a bank of
cooling tubes.)
or role of the ship's refrigerators,
size
are cooled by
or compartments
rooms
forced
Refrigeration
the
solenoid
The
air circulation
Conditioning)
Whatever
refrigerant.
stop the compressor.)
The
5.3
the
suction
resulting pressure drop in the compressor
line will operate
a low pressure
cutout valve and
emergency
requirement on all
the
de-energises
valve to stop circulation of
lights
falls to the preset
temperature
level,the thermostat
105)
Services
Electrical
Ancillary
switch
is usually
relay that
is fitted
this
of a current-operated
of its rated
speed,
out of circuit. For
80%
the
form
adjacent
to
in
the compressor.)
toxic gases that
are
irritants capable of causing
produce
they
respiratory
QUESTION)
death.)
If
Additional
components
cycle may
include
basic refrigerant
heat exchangers,
to the
filter
driers,
as
thermostats,
relays,
overcurrent
For
units
the
compressor
ANSWER)
and
controls
defrost
The start winding
(being
a higher resistance than
resistance check should
trips.)
bigger
than a domestic-sized refrigerator,
be a threemotor will invariably
a reciprocating
compressor.
phase type driving
be a single-phase
domestic version will usually
a rotary
motor driving
compressor.)
could
common
accumulators and pre-coolers.Also required
are the operating
and protective controls,such
markings are unknown,
you identify the start, run and
terminal
connections?)
terminal
motor
the
how
The
Using a multimeter
find
the
run
identify
rated) has
winding, so a
the terminals:)
the low resistance
range,
that have the highest
them.
These
are the start
The remaining
terminal must
on
terminals
two
resistance
between
and run
short-time
the
terminals.
be the 'common'.)
The basic refrigerant circuit
expansion system usedfor
vegetable roomsis outlined
Each cold room is fitted
with
of
a direct
the
cooling
(or primary)
of meat and
Figure
5.5.)
in
between
operates a solenoidvalve
limits. The quantity
of refrigerant
system
is regulated
by
the
This valve is controlled by
connected by
vapour return
that
a thermostat
set
temperature
in
flowing
valve.
expansion
the
phial that is
tube attached to the
a capillary
at the outlet of the evaporator.)
pipe
a liquid
Connectone
and
other
terminals
the meter onto the common
the other meter lead onto
the
turn
and note the readings.)
of
lead
touch
terminal
in
The highestreading indicatesthe start
terminal.
The other
connection.
remaining terminal
Typically, the run winding
and the start winding
is 6-22
O.)))
winding
is the
run
is 1.5-6
0
106
Marine Electrical
Practical
Knowledge)
Discharge
(hot gas)
line)
Condenser)
Compressor)
Liquid
receiver)
Power supply)
Starter)
Suction
line)
Solenoid
valve)
Expansion
valve)
())
Superheated
vapour)
vapour)
Liquid
Figure 5.5 - Refrigeration
circuit)
o)
Control
-------\037
relay)
\037)
Run)
\037
\\
VAG)
\\
\\
Gammon
c1
terminal)
/
/
/)
5.6 - Basic
Figure
The
main
refrigerator
compressor motor control)
control device in the
temperature
is the thermostat which senses
the evaporator temperaturevia a capillary tube.
The set temperature is adjusted by a control
knob that tensions the control
the
spring
against
of
the
bellows.)
pressure
For motor
included
protection,
as part
the compressor.
a bimetallic
OCR
trip
is
of the control
relay
alongside
The motor supplycurrenteither)
a bimetal strip or disc
passes
directly
through
or the bimetal
is heated
indirectly from a small
resistance heateralongsideit. A motor overcurrent
will
cause
the bimetal
to deflect and cause a snap
action switch to open.)
Figure 5.7 shows the completecircuit
domestic refrigerator (ie without
timers,
defrost or air circulation fans).)))
of
a simple
automatic
Ancillary
107)
Services
Electrical
0
Ll)
switch
Door
.-.--
/
Relay
VAC
Run
Cabinet
R
light
I
I
i
OCR
f
I
-
0-
i .
I
\\
\037
S
'\\
Start
Thermostat
5.7 - Domestic
When
the
--....,
............-)
refrigerator electric circuit)
closes,
allowing
the
motor
run winding
through
rises, the
temperature
evaporator
thermostat switch
flow
current
and
the
Air
to
the start
into
will now
motor
The
causing
where
motor
will
When
only.
begin to a\037celerate
to cut
incoming
to allow
its run
the
the
motor
out the refrigeration circuit
defrost
bimetallic
is
and
switch
initiate
a
to 45 minutes
hours
with
depending
Some
thermostat
heater
(to
to four
up
controls the
for
prevent
incoming
has
the air
mixture
relative
air may have to
heated
may have electric
duties such as a dewpoint
on the cabinet in the
sweating
there
may be condenser and
driven
by single-phase,
evaporator fans that are
shaded-pole type motors.)
aspects
of accommodation air
the power equipment
comprises
for the compressor(s), fans
starters
(A/C)
and
motors
high
freezers
Additionally,
electrical
The
or
and
include
will
equipment
various
and a compartment divider
panel
(to prevent sweatingon the panel).)
area)
the
winter,
and seawater coolingpumps.
defrost cycles in
stile heater
freezer
In
the
heating
and
the
and have water added to achieve
inlet conditions. In most plants, the bulk of
is recirculating
the mixture
air, with fresh air intake
one third of the total required. The
about
forming
air is a statutory requirement,
of make-up
amount
17 m 3/hr and 28 m 3 /hr.)
between
typically
be
of
on the fridge/freezer design.)
and
refrigerators
heaters fitted
humidity.
conditioning
defrost heater in or below the evaporator. Most
defrost thermostats closeat 20\302\260F:t 50 and open
at 550 :t 50. Defrost periods may vary from 15
24
condensation to occur until
then
the desired specific humidity,
to the required delivery
temperature
an
is generally
defrost heater circuit.The timer
contacts.)
electronic relay with a set of changeover
A
duty, the usual method is to cool the
the
air to a temperature below
dewpoint
correct
common
way to achieve automatic
is to use a time
of the evaporator
defrosting
summer
For
from
off.)
most
The
cools,
winding.)
temperature, the thermostat resets and
switched
heats,
cleans
current
to reduce
winding
off. The
will
drop
start-relay
on the run-phase
now
run continuously
reaches its set
the evaporator
standstill,
to a level
is a process that
and circulates air and controlsits moisture
a definite
The air must be deliveredwith
content.
relative
and
specified
humidity.)
temperature
relay
the solenoid
current
Conditioning
Air conditioning
coil. This current is initially
causing
high,
to close the relay switch to allow
solenoid
C
\\
\\
\\
1
Figure
Rotor
low
together with
Associated
control
solenoid
valves,
and temperature switches,
loss of
for overcurrent,
etc.)
oil pressure,
compressor
pressure
cutouts
safety
low
refrigerant,
electric
used for the
The usual air conditioning
system
accommodation spaces of cargo ships is the
5.8. In
central single duct type, shown in Figure
the
s
erves
its simplest form, a single compressor
whole
accommodation.)
The compressor
reciprocating
of 20-100 kW,
type
is generally a multi-cylinder
in the
with a power rating
although
rotary
vane
or screw)))
range
Marine Electrical
Practical
108
action
Knowledge)
be encountered.
may also
compressors
Largepassengervesselsmay
a total
have
requirement of more than 5 MW for the AC
air delivery
to the
compressor drivesto maintain
hotel and staff accommodation
areas.
Capacity
control of the reciprocatingcompressoris by
automatic
using
of cylinders
unloading
servo oil pressure.)
The compressor,air
by
and
1.
seawater
any
used
be
2.
for separating
oil in an
oil reservoir.)
the
4.)
3.
out
in
instructions.
Fresh
with
accordance
In
the
particular,
Re-circ. air
4.
L...
\037
\037
.L...
\037)
it is
being used in the
area.)
and tools
the
unit
with covers
unit
with
tools
in suffocation
Be aware that
in
refrigerants
the
presence
used
in the
death.)
Plenum)
Heater)
air
C27)
VAC supply
Heating
and
scheme and main
components)
and
of an open flame
\037PPIY
AC cabinet)
or meters
or electricalarc, producetoxicgasesthat are
severe
irritants capable of causing
respiratory
Cooler)
Condenser)
clear of
is running.
death.)
G)
5.8 - Air-conditioning
damage
with
Use caution when working
a refrigerant
or
or refrigeration system in any closed
confined area with a limited air supply.
air and can cause
Refrigerant will displace
I
Figure
to run
careful
inputl)
Ventilation
clothing
necessary
systems,
low oil)
compressor's
Fan)
I)
hands,
removed, be very
possible
the manufacturer's
air input
I
glasses.
permanently
oxygen depletion,resulting
the refrigerant
of control and
Regular inspectionand testing
be
safety thermostats and pressurestats should
carried
Keep your
If
the compressor
for heating
crankcase oil and
from
can
the eyes.)
of connections and correct operation
heaters
must also be performed.
may
or safety
goggles
Refrigerant liquid
electric
Heaters
wear
Always
the fans when the refrigeration
of connections, I R (megger)/continuity
checking
tests and running
tests
as described
in Chapter
Inspection
with refrigeration
working
equipment.)
Routine electricalmaintenanceand fault finding
on the motors and starters will involve
cleaning,
of
when
be
must
precautions
safety
followed
strictly
plant room.)
conditioning
Precautions
The following
pump are
driven by simple
AC
fixed-speed,
three-phase
induction
each
with its own starter and
motors,
board fitted in the air
suppliedfrom a distribution
fan
be tested
should
circuit
trip
periodically for correct operation.)
Safety
control
valve
and
alarm
pressure
power
'rom
cabinet)))
to cabins)
to arrive at the hull
allowed
Protection)
Cathodic
5.4
negative
The
of a ship's
surface
outer
electrochemical
attack by
flow between areas of the
electric
different
currents
corrosive
which
hull,
to
that
is subjected
hull
hull
to
by
fitting
to the
The
(positive) or cathodic(negative).)
shows
5.9
from anode to
iron
that,
in
cathode
at the
ions
the
hull,
respect
DC
of
the
to changeto leadperoxide
Pb0. The
it just
that
will
the
cause
impressed
that flows in the
current
circuit.
complete
must
be critically
as
this
beyond
of OH ions
of release
rate
sponginess
and flaking
of the anti-fouling
the electrolytic
action will
form
paint.)
positive iron
ions
to form
Initially,
ions
Pb0
2
on
they
ferrous
hydroxide Fe(OH)2'This ferrous hydroxide is
oxidised
by dissolved
oxygen to form ferric
In this
which
is
rust.
hydroxide
way, the
Fe(OH)3
anodic area is gradually
corroded
while no
away
corrosion takes place at the cathodicarea.)
the
naturally
complete
corrosive
action can be overcomeif
hull is made cathodic, ie electrons are)
Anodic
,,,---
I
I
I
I
I
I
I
I
J
I
------._---,
+
+
Fe
of
value
current
protection
can be
determined by reference
electrodes.
These are
either of zinc or silver attached to the hull, but
insulated
from it, below the waterline.)
o)
------ -----.....
.......
\"
.....
\"-
'\\\\
o
J
,
I
/
\037
0
:
I
4;:::
\037
t)
Thecorrect
area)
!
t
,
J
\037
......
(.)
Q)
i:U)
o
.
a>
()
s-
::J
o
(/)
s-
.#
//
\"\"
Insulated
...,
o
anode
',\\
a>
3:
o
Q.
OH)
,----)
o
---------_..../)
Cathodic
_____J
o)
area
\037-//))
Electrons'flow)
Seawater)
Seawater)
Ship'shull)
Natural
Figure 5.9 - Cathodic
Ship's
corrosive
protective
action)
action)
the
of the anodes and when this skin is formed
the
action
reduces.
The anodes take on a rich
brown
lead-acid battery plate)
appearance
(positive
and in service
are expected
to last 7-10 years.)
surface
further
This
is
the original
overcomes
corrosion current and gives riseto an
protection
potential
2
of such a value
is to produce
electrons
ions
negatively charged hydroxyl
(OH) by
electrolysis of the seawater. These negative
flow through
the sea to the anodic area where
with the
anodes
value the increase in the
charged
cathode,
OH ions now pass to the
causing the lead surface
charged
negatively
insulated
lead
The value of protection current
controlled to just prevent
corrosion,
flow
electrons
positively
leaving
anodic area. At
effect of the arrival
combine
a positive
to the hull.)
applying
with
potentials.)
Dissimilar metals, variations in structural
and
chemical
in
hull
and
plates
uniformity
welding,
differences in paint thickness
and quality, water
and
aeration
all combine to
temperature, salinity
cause areas of the hull to become either anodic
Figure
and
hull
potential to them
produce
leave the
iron ions. This is achieved
or platinised titanium
produce
positive
insulated
lead
anodes
are at slightly
and
surface
no electrons
but
ions
hydroxyl
109)
Services
Electrical
Ancillary
Impressed
hull)
current
protection)))
110 Practical
Electrical
Marine
Knowledge)
The voltage measured betweenthe hull and
reference
electrodes
of an unprotected ship with
seawater
as an electrolyte
is:)
Zinc electrode
450
Silver electrode)
600 mV positive to hull)
mV
to hull
negative
the protection
protected,
current
make
the hull 200 mV more negative,
ie a zinc reference
will
250 mV
register
negative to hull and silver 800 mV positive to hull,
as shown
in Figure 5.10. The reference
When
satisfactorily
will
Cathodic
does
protection
molluscgrowth
anti-foul
the
on
(poisonous)
Typical
reference
shown
in
not appear to deter
ship's hull, so a top coat of
paint is still necessary.)
and main anode outlinesare
5.12.)
Figure
protection
Monitoring facilities in the cathodic
control cabinet may provide measurements of:)
electrode
electrode
be used
therefore,
may,
voltage
protection, but more importantly,
signal source to automatically
of protection current.)
Cathodic
protection
systems
control
The
electrodes,an amplifier
transformer rectifier
individual
consist
ships
titanium)
platinised
below the
places
system.
and
one
anode current
electronic
thyristor
5.11 outlines
Figure
densities
range
150
hull area, speed, water
will
all
paint condition
currents to vary.
hull
The
potential
regulated
system.)
Although
the
reference
facilities
monitoring
day check, they
fitted
are
and the
electrodes
a
reasonable
provide
day-toonly
measuring
in
the
vicinity
electrodes.)
or more
control is usually
regulated
by
controllers and the diagram in
a typical scheme.)
from
and
should, however, remain constant in a properly
of the
The control
monitors
the
equipment
automatically
size of anode current required,which
will vary
with
the ship's speed, water temperatureand salinity,
condition
of paintwork, etc. Typical anode current
the
underwater
the anode
is moored singly or stopped at
can be taken between
voltage
readings
a portablesilver or zinc test electrode and the
ship's hull. This portable electrode is lowered
2-3 metres below the water surface and as close
as possibleto the hull at specified positions around
the ship
When
10 mA/m 2 to 40 mA/m
the
temperature/salinity
cause
potential)
current.)
anode
in
voltage (hull
current
anode
Changes
in
units.)
The
output voltage
.
fitted
assembly
amplifier
total
comprises reference
equipment
.
the value
AC distribution
Hz three-phase
electrode
.
waterline and control
that automatically
equipment,
the
anode
current
to
the
value.
regulate
required
Direct current is supplied
to the anodes,
after
transformation and rectification,
from
the ship's
440 V 60
Reference
to monitor the
it is used as the
regulate
(leador
of a number of anodes
fitted to the hull,
at selected
.
2
for
of painted surfaces, and 100 to
protection
mA/m 2 for bare
steel surfaces. The total
for a hull in good
condition
impressed current
may
be as low as 20 A. Maximum
controller
outputs
may be up to about 600 A at 8 V.)
sea,
the ship.)
Checkthe manufacturer'sinstructions
the
storage
regarding
and setting up of the portable
electrode.Some
have
to
be
immersed
in
a plastic
of seawater for about 4 hours beforethe
hull
test.
With the cathodic protection switched
on and working
the voltage
measured
normally,
between the hull and a silver/silver chloride
bucket
mV
portable electrode should be 750-850
using)
Positive
Negative
1
-L
250
mV
800 mV
\037
,..)
Figure
5.10 - Protection
voltages)))
Ancillary
.3 x AC source
to.)
r r
r
DC power
\037 _ __
supply)
Electrical
Isolator
switch)
Set - value)
Electronic
Protective
anodes)
regulator)
Step-down
transformer:)
i)
Rectifier
\037)
I)
+)
To reference
anodes)
,
/
Protective
anodes)
', 0 ,/
'R/)
../,\037\037....,.)
.
\037 --.,..)
.
<
f \\\037'.'
1. i
' -:,\037\037.:
.-
.\
..'\037
\302\267
I
\037
<
1'\"\",'.\037
,,'
j.
,,,1;
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\302\267\302\267
\302\267 ,
\".
---
.u.
\037.,
(:_ ;\037\037
- .\037\037\037\302\243..
,.....
[
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-. \"':\037\037.'
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\037 \" \037
-Ir
\037JJ...':\037
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,
\\fJj I;.
. .;: :)
.\"\037.\037\\.)
I)
Figure
5.11 - Ship
anodes and impressed current
control
system)
Lead-alloy
Fibreglass cover
Bores
to silver-
chloride
compound
A
.
Figure 5.12 - Reference
and
main
.
.
. ..
.
.)
------
Reference
glass
Main anode)
anode)
anode
strips mounted in a
moulding
fibre insulating
construction)))
Services
111)
112 PracticalMarine
to the
When
ensure
the
that
main
anodes
paper
paint contamination.)
to prevent
To ensure that the rudder and propeller screw
(and stabiliserfins for ferries and passenger ships)
receive the same degreeof cathodic
as
protection
the hull, it is necessary
to electrically earth bond
theseitemsto the hull. The rudder stock may be
bonded by a wire braid linking the top of the stock
to the deckhead directly above it. Carbon
brushes
on the rotating
rubbing
shaft
propulsion
to the hull. A periodic
A
occasionally
may
stick in
maintained
properly
battery will
power when required.
makes
a battery
the key element in
of essential and emergency power
This feature
provision
storage
electric
supply
instantly
supplieson board
manufacturer's discharge curves must
routine
power supplies, eg for radio
telephone
exchange, fire detection,
circuits,
etc, are often supplied from
general alarm
a set of batteries
worked on a regular charge/
discharge
cycle.)
a
10 hour
will
have
fallen
equivalent
the battery room
ventilated, clean and dry. Both
hydrogen gas during
charging,
naked flames must be prohibited
the batteries.)
in that
in
fails.
nominal
Ships'
voltage
The two main
are:)
and
batteries
are usually rated at a
of 24 V DC.)
types
of rechargeable
battery cell
\302\267Lead-acid
.
adjacent
types
generate
so smoking
and
in the
vicinity
of
to lead-acid
cells.)
Ni-cad
cells
Acid
because
must never be placed near alkaline
cells
of the risk of rapid electrolytic corrosion
and
reasons,
to both batteries.
damage
never
use lead-acid battery
maintenance gear (eg hydrometer,
bottles, etc) on an alkaline installation,
topping
or
For
up
vice
versa.)
Battery maintenance
dry,
includes keepingthe celltops
the tightness
checking
of terminal
a smear of petroleum jelly
applying
connections
to prevent corrosion.)
nuts
and
to
role to give power when the main
a standby
supply
eg for emergency
emergency
lighting, are used
supplies,
decks
are
be well
should
batteries should be coveredwith acid-resisting
paint.
paint should be used near
Alkali-resisting
and
generator startup
checked
types of battery
for both
installations
Battery
similar
clean
battery
be
discharge, a lead-acid cell voltage
to approximately 1.73 V. The
figure for an alkaline cellis 1.14V.)
After
to metalwork
ships.)
equipment,
Emergency
the
details.)
for such
similar
Essential
parallel
cells
More
to increase
is rated
in ampere-hours
battery capacity, which
The
is
(Ah).
battery
capacity
usually rated in terms
of its discharge
at the 10 hour rate. A 350 Ah
35 A for
battery would be expected to provide
10 hours. However, the battery
will generally
have
a lower capacity at a shorter
rate.
The
discharge
Steelworkand
Supplies)
Battery
the
and
as the
holders.)
brush
5.5
is worthwhile
earthing
brusheswear away
their
in
main
effectively bond the shaft
inspection of such
a nominal 24 V.
to produce
series
in
may be connected
electrodes are coveredwith
and reference
tape
with
hull.)
docked,
dry
Knowledge)
the electrode being positive
a multimeter,
respect
Electrical
alkaline.)
The nominal cell voltages of each type are 2 V for
lead-acid
and 1.2 V for alkaline.
Twelve lead-acid
cells or twenty
alkaline
cells must be connected)
Be careful
when
the battery electrolyte
handling
when
a
(eg
using hydrometer to check its
specific gravity). Use protective rubbergloves
and
eye
goggles
when
handling electrolyte.
Insulated spanners should
be available
for use
on cell connectionsto prevent
accidental
shortof
A
terminals.
short-circuit
circuiting
battery
across
the terminals of just one cell of a battery
will cause
a blinding
the cell being seriously
flash,
with
damaged.)))
the probability
of
QUESTION)
cell
alkaline
An
hydroxide
while
acid. Both
are
Ancillary
Electrical
Figure 5.13 showsthe principal
features
The state of charge
best indicated
be
you
in
A fully
has an SG of
about
1270-1285), which
ANSWER)
In
both
and skin with
rapidly
water. The electrolyte of alkaline
wash eyes
cases,
of fresh
plenty
causes
cells
skin burns that
be treated
should
washed
with boracic powder and the eyes
out
with
a solution
of boracic power - one
teaspoonful
to
Sulphuric acid splashescan be washed
solution
salt to one pint
saline
- two
of
cell
(often
written as
to about
1.1 (or 1100) when
cell voltage also falls during
can also be used as an
state of charge.)
may be safely discharged until
drops to approximately 1.73 V
while
load current).)
delivering
battery
voltage
indicate that
necessarily
state. Note that
charged
water.)
For both types of battery,
should be in the battery
lead-acid
the
cell
1.27-1.285
The open circuit (no load) battery
can be misleading as a high
value
a
with
of household
teaspoonfuls
of the
(measured
of water.)
a pint
and
indication
A
lead-acid
its value
discharge
as shown
charged
falls
The
discharged.
fully
of a
by a lead-acid battery is
on the electrolyte specific
a hydrometer,
by using
5.14.
Figure
held
a test
by
(SG),
gravity
treatment
would you apply should
with
either
splashed
electrolyte?)
aid
first
What
the
cells
the
SG
aid equipment
compartment.)
not
does
are in a healthy
values quoted
temperature
of 15\302\260C. Corrections
to the
at any
ambient
temperature
are:)
------...----------)
Positive
terminal)
Positive
electrode
other
readings
voltage
above for lead-acid cells are basedon
first
an
ambient
SG value
*. ----\037\037
Negative terminal
-___
-----
----*)
.
-
.
'....
. ......,....
Case
o'
....,
uii.\"
. ..\", C\".
'i.\"
\037\037\037\037\037...'.........
\037OO
\037\037\037,.J\037'{;:::::::::
ft
.....
II'
,
J
NegatIve
plate
___)
]
I.
Figure
5.13
- Lead-acid
edge)
, . , .....,.........
...............
.'
-___)
cell construction)))
I\",
\037
\037\037\037...
i\037\037
\037\037\037\037\037\037\037I:I\037:
II\"
o!
1\037.\037\037\037\037U\"Udld;
D'
11\037\037\037II\037:ll,
\037\"II\037,fl)
113)
cell.)
lead-acid
has an electrolyte of potassium
a lead-acid
cell uses sulphuric
diluted
with distilled water.)
Services
Perforated plastic
separator)
.
Marine Electrical
Practical
114
Add 0.007 to reading
Knowledge)
for each 1DoC
above
15\302\260C)
.
from reading for
subtract
0.007
below 15\302\260C.)
outlines
5.15
Figure
the principal features of
The state of charge of
an
alkaline
battery
SG value.
cannot be determinedfrom its
electrolyte density does not change
falls
discharge cycles, but gradually
lifetime of the battery.)
New
1 DoC
each
an
cell.)
alkaline
When
cell
The
1)
,\037oo)
during
charge/
during
the
I
!.2$1
p\037
..\037-)
1.280 SG)
cells have an SG of around
this reduces to about 1145(which
Float dilute acid liquid
within glass syringe)
1190.
may
5-10
1.1
when
the
cell voltage
High float = high SG
Low float = low SG)
has fallen to
V.)
Figure
Positive
5.14
-
_---
terminal)
testing)
Hydrometer
Low
pressure
flame arresting
*)
co-*- _)
.\037')
Positive
Negative
terminal)
Negative
electrode
Negative
plate)
electrode edge)
*)
\\)
'\\
Jk
--
----------_
edge)
=)
Distance
*)
plate)
-------)
------.---)
..llm.lil\037
.i
..
h,.,tl\037lI/ill/l,
Fibre
..
mat separator)
------.-)
.lli'!Jllillllllll i
nbuli'! i 'I
i
II
II!II.Illlllll
II t
. I
\"'::,:\037IUI/l\"f:
n\037.1
Case
____)
....................
*)
Figure
5.15
- Alkaline
cell construction)))
11.)
3.)
alkaline
be discontinued
about
1.150 SG)
!2S1P)
the
years depending on the duty cycle),
must
be
renewedor
the
electrolyte
completely
of alkaline cells should
battery
replaced.
Discharge
take
.)
.\037
\037
J:'ZCJ)
. . ::.. \"1filii
IflU,
. ;II\037
i
un
..::j'*)
----\037--. Perforated
plastic separator)
vent)
Battery charging equipmentuses a transformer/
to supply the required DC
arrangement
cells.
The
to
the
size of voltage depends
voltage
or alkaline) and the
on the battery
type
(lead-acid
level above the plates. Exposureof the
rectifier
to air will
mode of charging,
On all ships and offshore
essential services that
cycle,
Check the
charge/discharge
float charge.
eg
boost charge, trickle
or
manufacturer's instructions for
required charging voltages.)
of the
details
to exceed
Do not allow electrolyte
temperatures
A lead-acid cell will
about 45\302\260Cduring charging.
arrangement.)
freely
charged,
fully
are more robust,
cells
alkaline
Generally,
mechanically and electrically,than
Nickel-cadmium
cells will
periods
recharging
without
lead-acid
The
cells.
for long
t.heir charge
are ideal for standby
with
a float charge to
when
the main
supply
hold
so
duties. They also operatewell
provide a reliableemergency
For all
batteries
rechargeable
sealed type), it is essential
(caused during
the
with
and
gassing
of distilled
addition
(other than the
to replace lost water
by normal evaporation)
water to the correct)
the
vital
cell
plates
battery.)
are
there
platforms,
are
by an
a complete
during
supply
power
uninterruptible
shown
arrangement
in
5.17
Figure
is typical
of a continuousUPSDC-supported
supply
The essential
DC services are normally
system.
supplied
through
charges
from
the 440
main
V
charger no. 1 which
its battery. During
battery no. 1 maintains
power fails.)
of
life
These can be for battery-supported
DC supplies
or AC supplies, both of which can
be configured as continuousUPSor standby
UPS.
5.16 shows an AC-supported UPS
Figure
the
period. The only
charging
gases throughout
alkaline
cell is when
indication of a fully charged
its voltage remainsat a steady maximum value of
about 1.6-1.8V.)
gas
an alkaline
rapidly
supported
or UPS.
but
the
reduce
power
system
trickle
continuously
a loss
of main
a transitional
power,
supply
while
AC
to load)
AC
to load)
the emergency generator restorespower
to the
no. 2. Either
board and so to charger
emergency
battery is available for a few hours if both main and
emergency generators are unavailable.)
..)
Inverter)
Charger
AC supply
1
Battery
l
Inverter
Charger)
AC to load)
r
Loss of supply)
-)
111\037--III\037.
t
Battery
Normal recharge)
\037111\037--I11\0371)
mode)
Emergency
Continuous
UPS system)
..)
Inverter)
Charger)
AC supply)
Battery
Normal
5.16
- UPS
r)
Loss of supply)
Battery)
I-III\037--III\037I)
systems)))
I
'I'\037
--1111-1)
Emergency
recharge)
Standby
Figure
Inverter)
Charger)
AC to load)
1)
115)
loss of main power. Such services include
switchgear operation,navigation
lights,
foghorns,
fire and gas detection, internal
communications,
radio communications
some
and alarm systems.
To
avoid
the loss of essential services, they
are
cell
when
Services
Electrical
Ancillary
UPS system)
mode)
116 PracticalMarine
Electrical
Knowledge)
critical emergency lights
UPS within
battery-supported
Some
internal
where)
luminaire,
have
the
3 x 440 VAC
Main
an
its battery charge is continuously
conditions.)
non-emergency
3 x 440 VAC
Switchboard)
Emergency
maintained
during
Switchboard)
I
\037)
l)
f)
\037)
Three-phase transformer)
Charger
No.1)
Bridge
rectifier)
Blocking
diodes)
Charger
Blocking diodes)
I
I
I
Battery
No 1)
DC
DC services)
Figure
5.17
- UPS
1)
1)
----1-)
DC battery
charger)))
busbars)
I
I
I
-L-)
Battery No 2)
No.2)
Chapter
Six
Special
Electrical
Hazardous
The
Atmospheres)
may be ruined
of a design
intent
safety
maintenance
by
poor
practice.)
electrical
This means that
out by
must
maintenance
a competent
Temporary
person.
is not
transport,
of oil, gas
to special
on the
recommendations
Electrotechnical Commission (IEC)standard
on Ships'.)
Installations
a non-hazardous
60092
cargoes.)
avoid
to
equipment
caused
explosions
is to not install
such
hazardous areas. Howeverexplosion(Ex)
is permitted where it is
equipment
where
and this chapter will consider
necessary,
how it should
be
into
fall
as
or normally-safe
spaces.)
dangerous
is an area where flammable
space
or vapour
mixtures might
be
normally
to occur.)
Examples of the
to
and
maintained.)
Zone
industry
be:)
could
ships
Zones
Hazardous
on
style
zoning when applied
0
Interior spaces
6.1
either
dangerous
expected
in the
and
zones.)
equipment
protected
how it is used
used on tankers, electrical
and graded largely on
On tankers, areas aredesignated
gas-air
by
it
when a tanker is alongside,parts
of
the hazardous
zones of the shore
in areas
of the ship that may not
facility,
possibly
be considered unsafe.)
normally
A
The bestway
if
In addition,
it may
where
explosive
Spaces in tankers
gas/air
are called
mixtures may be expected to be present
all other
areas
dangerous or hazardous. While
being regarded as 'safe', specialcarewill always
on any vessel carrying hazardous
be required
and,
operation
or safe area.)
is not
practice
is manufactured
this
the basis of such
'Electrical
electrical
area
be
equipment
International
normal
Zone 0, 1 or 2 is assumedto
not classified
An
While
Authorities
electrical codes of practice.
Statutory
and Classification Societies generallybase
in
will only exist for a short time.)
occurs,
that
to occur
likely
gas atmosphere
an explosive
in which
area
An
forbidden.)
their
operation.)
Zone 2
with
the wrong sized
arrangements, refitting
the
to employ
components (eg lamps),failing
etc
are absolutely
correct number of cover bolts,
installations
Ships and offshore
process and store bulk quantities
are subject
and liquid chemicals
in normal
occur
to
gas atmosphere is
an explosive
in which
area
likely
be carried
periods.)
1
Zone
An
for long
or
continuously
to be in a less safe condition
in its original certified state.)
gas atmosphere is
an explosive
in which
area
present
equipment
it was
Zone 0
An
Maintenance must not cause the operationof
than
for
Practice
of oil cargo
tanks,
pipes,
pumps, etc.)
Zone 1
Tankers)
Enclosedor semi-enclosed
spaces
on
the
deck
the boilerfiring area on a gas carrier
as a fuel and battery rooms.)
using methane boil-off
of a tanker,
Petroleum
and
chemical
hazardous areas is to
practice for
into three zones
of hazard
degree
industry
them
divide
(0, 1 and 2) that recognise
and indicate the likelihood
mixture being present.)
the
of
an
explosive
gas-air
Zone 2
Open spaces on
may
change
when
the
deck
of a tanker
alongside).)))
(although this
118 PracticalMarine
6.2
Electrical
Knowledge)
material is mixed with air,
to be a certain concentration of fuel
within the mixture for it to
(flammable
substance)
it the
of the fire triangle).
burn (making
fuel element
Fire
the
Understanding
Triangle)
Beforea
elements
can
explosion
must
be present,
are:)
triangle',
or
fire
that
to as the 'fire
When
a flammable
there
needs
The flammable
take place, the three
commonly referred
of
catch
fire or explode.
of supporting
with sufficient
energy to
combustion(fuel)
of ignition
\302\267source
initiate
\302\267an
combustion
For example,a mixture
of oxygen, usually air
Lower
limit
flammable
Lower explosive limit
Below
known
\\)
the lower limit of the flammability
range,
as the lower flammable
limit
there
(LFL),
flammable material in the mixture to
combustion.
The LFL refers to the leanest
support
mixture that can sustain
a flame.)
Upper flammable limit
Upper
Fuel)
extinguish
elements
(UFL)
is insufficient
will
gas
in tanks
atmosphere
them
Using inert
or
prevent
a fire.)
within
refers
to the point
to generate
the richest
gives
air
or support combustion. The UFL
flammable mixture.)
Fire Triangle)
of the
limit
there
which
(UFL)
limit (UEL)
explosive
The upper flammable
above
any
(LFL)
(LEL)
is insufficient
Heat)
The removal of
of
burn
its composition lies within
the
flammable
material
The
of
combustible
proportion
range.
in the mixture
is expressed as a percentage by
in air,
volume
of vapour
the
and is delineated
by
and
lower
flammable
limits.)
upper
(oxidiser).)
Oxygen
and
unless
(heat)
supply
adequate
within
gas and air cannot ignite
hydrocarbon
capable
material
flammable
\302\267A
range of concentrations
air that may
is the
range
substance
a particular
and pipes keeps the
of the flammable
outside
zone (Table 6.1).)
Flammable
Limit (LFL)
Upper Flammable Limit
Substance
Lower
Acetylene
2.3 vol. %
78.0 (self-decomposing) vol.
Ethylene
2.3 vol. %
32.4 vol. %
Petroleum
Benzene
1.2
Natural gas
4.0 (7.0) vol.
Heating oil/diesel
Methane
-0.6 vol.
vol.
Propane
Carbon disulfide
City gas
Hydrogen
Table
6.1 - Common
-8 vol. %
vol. %
-0.6
spirit
4.4 vol.
1.7 vol.
0.6 vol.
8 vol.
%
13.0
(17.0)
-6.5
vol. %
%
16.5
vol. %
%
10.9
vol. %
%
60.0
vol. %
30.0
vol. %
77.0
vol.
%
%
4.0 (6.0) vol.
4.0 vol. %
substance flammable limits)))
%
%
%)
vol. %
(UFL)
%
low ignition
15
I
Too rich to burn
10% UFL
Variation of the upper
in air)
limit of flammability)
:I:
-o
CI)
C)
5
high ignition
energy, can be
we can see that it is possible that gases
or vapours, when
concentrated
between
their UFL
and LFLlimits and in the presence of air, might
be
by heat
generated
electrical
various
from
such as:)
sources,
limit of flammability)
ignition
it is very
Therefore,
ignited
Variation of the lower
(so
its very
with
high ignition
difficult
to ignite)
surprisingly
has a low
temperature
and
temperature
ignition
high
however,
Acetylene,
easy to ignite).Methane,
I)
c
CIJ
co
o a;C E
\302\260
::J
of - 10
co\037
o
o >-c\037
>-
a very
low ignition
and
energy
a very
has
hydrogen
but
energy,
temperature.
Inert atmosphere)
\037
oCI)
...
CI)
a..)
for Hazardous Atmospheres 119)
Table 6.2 shows that
20)
CI)
...
::J
X
\037
CI)
\037
Practice
Electrical
Special
2% LFL
in air)
TOO weak to burn
I
I)
10 I
5)
20
15)
I
11%)
21% (air))
Percentage of Oxygen in the Mixture
(By Volume))
Figure
6.1 - Oxygen
content in a hydrocarbon/air
shows us that, for
once the limiting
mixture,
gas/oil
This example
.
arcing betweena live
.
an internal
enclosure
.
.
a hydrocarbon
oxygen
combustion is not
presence of sufficient fuel.)
is reached
concentration
the
despite
possible
mixture)
it is also necessary for ignition
Finally,
of the triangle) to take place.)
(the
last
part
arcing
within
hot
earth
an electrical
spots
an electrostaticspark dischargebetween
bodies
or between a charged body
charged
and earth.)
6.3
and
Groups
Explosion
Classes)
Temperature
ignition energy (MIE) is the minimum
to ignite a combustible
of
for
vapour,
example by means
an electrostatic
discharge.)
and
conductor
fault
causing
overheating
contacts
switch
between
\302\267
Arcing
o)
Minimum
of energy
required
or dust cloud,
gas
amount
The auto-ignition
or kindling
temperature,
point, of
a substance is the lowesttemperatureat which
it
will spontaneously
ignite in a normal
without an external source of ignition,
atmosphere
such
as a
flame or spark.)
Examples these
of
Gas
temperatures
are:)
Auto-Ignition
Minimum
(OC)
Acetylene
305
Ignition
Energy
(mJ)
0.02
Butane
365
0.25
Hydrogen
560
0.02
Methane
595
0.29)
6.2
-
Auto-ignition
temperatures)
flammable
gases
in which
electrical equipmentmay
grouped according to the
have
explosion-protected
to operate
amount
are
of electrical
to
energy, in the form of an arc, that is needed
the
This
classification
determines
ignite
gas.
the
between the flameproof
safety
gap needed
enclosure and
energy
Temperature
Table
Explosion Groups
The
does
its
cover
to ensure
that
sufficient
not cross.)
The gases associatedwith the mining industry are
fire-classed as GROUPI.All other industrial
gases
are classed as GROUPII and these are split into
three
to their ease of ignition.)
sub-groups
according
Group
IIC is the
most severe group. Gases in
be very easily ignited.Electrical
group
certified
as suitable for Group IIC is
equipment
also suitable
for liB and IIA. Equipment certified as
suitablefor liB is also suitable for IIA but not for IIC.
Equipment certified for IIA may not be used with
this
groups
can
liB or
C.)))
120
Marine Electrical
Practical
Use
Group
Equipment
Safety Gap for
Group
Explosion
Electrical
I
Group
Knowledge)
FlameproofEnclosure
for mines
equipment
Fire damp protection
EEx...I
Electrical
II
Group
for areas
equipment
mm
IIA
>0.9
118
0.5 mm
IIC
<0.5
by explosive
endangered
gases
to
mm
0.9
protection
Explosion
Ex. ..II
mm)
Table 6.3 - Explosion Groups)
The
is another factor that will affect
gas grouping
the design and construction of equipment
to be
used in hazardous
zones.
Section
6.4 explains the
ratings used and
what
Temperature
Classes
they
mean
in
detail.)
more
The
class
temperature
of 40\302\260C; should
temperature
dissipate
apparatus
ignition
temperature
other
any
reference
be adopted, regulationsrequirethat
be shown on the equipment.)
temperature
heat.)
some
this
to note that the apparatus
gas
and
grouping
temperature class are not related.
For instance,
hydrogen requires very little spark
It is
important
energy
The
surface
maximum
temperature
As well as consideringthe protection
against
electrical
arc and sparks igniting
a flammable
consideration
must be given
to the
atmosphere,
surface
of equipment because most
temperature
electrical
is the
in the electrical
temperature of the components
It
and
fault conditions.
equipment under normal
is stated
with reference to a maximum
ambient
of flammable
gases
or
a flammable
is the lowest temperature of
liquid
a heated surfaceat which the gas/air or vapour/
air mixture ignites. Therefore, the highest surface
of any equipment
must always be less
temperature
than
the
of the surrounding
ignition
temperature
to ignite,
necessary
but
for ignition
classes
Temperature
introduced
for
electrical
explosion
group
II.)
the
surface
is very
temperature
high
(560\302\260C).)
T1 to T6 have been
rated
equipment
within
atmosphere.)
T-
IEC/EN
Class
NEC
505-10
Maximum Surface
T Class
NEC
503-3
CEC 18-052
Equipment
of
IgnitionTemperatures
of Flammable
Substances
T1
T1
450\302\260C
T2
T2
300\302\260C
>300
s450\302\260C
T2A
280\302\260C
>280
s300\302\260C
s280\302\260C
>450\302\260C
T28
260\302\260C
>260
T2C
230\302\260C
>230
s260\302\260C
T2D
215\302\260C
>215
s230\302\260C
T3
200\302\260C
>200
s300\302\260C
T3A
180\302\260C
>180
S200\302\260C
T38
165\302\260C
>165
S180\302\260C
T3C
160\302\260C
>160
s165\302\260C
T4
135\302\260C
>135
s200\302\260C
T4A
120\302\260C
>120
S135\302\260C
T5
T5
100\302\260C
>100
S135\302\260C
T6
T6
85\302\260C
>85
S100\302\260C)
T3
T4
Table
Temperature
6.4 - Temperature
classes and related ignition
temperatures)))
to all
class relates
Temperature
equipment
that
potentially
explosive
can
parts
Special
Electrical
Practice
of the
.
limiting
concentrations
with
.
into contact
come
lower
the
the
The temperature classificationwill
on items of equipment. If the hazardous
marked
area in which
you are installing equipment
temperature.
has gases or vapours
a low
with
temperature then you will
bigger T-number to ensure
not
need
ventilation.)
any hot surfaces
the hazard.)
If the
explosion
then
specifically
protection
order.)
requires
Electrical
on
different
Primary explosion protection
employed.)
covers
in
x)
all measures
-
6.2
Figure
atmosphere
explosive
of nitrogen,
addition
carbon
Ex identification
Basic
Marking SchematicDiagram
Protection
European
mark)
types for electrical equipment in
are:)
gas atmospheres
explosive
dioxide, etc))
Type of
of
requirements
of protection are based on
general
is identified by the symbol
'Ex' followed
the
of
indicating
protection
type
a letter
Protection
(the
areas
concepts.)
protection
Explosion
by
the
All types
60079-0.
EN
for hazardous
equipment
all
measures to be carriedout
that prevent a potentially
forming. These include:)
Inerting
cannot be removed
and rated electrical
designed
hazard
must comply with
with a
equipment
Integrated explosionprotection
.
121)
Protection)
Explosion
explosion
a defined
Atmospheres
equipment must be used.)
auto-ignition
that
ignite
be
As an example,an electricmotor
have
a
may
maximum surface temperature of 120\302\260C and would
be classed as T4.)
6.4
Hazardous
atmosphere.)
The bigger the T-number,
the equipmentwill
for
Standard
Principle
Examples
Symbol
General
Requirements
General
General
EN
60079-0
requirements
for the type and testing IEC
60079-0
requirements
of electrical
equipment
intended for the
Ex area
Increased
safety
e
y
l
r
its
or
equipment,
EN 60079-7
IEC 60079-7
to
only
Applies
boxes
component parts,
normally
does
not create
sparks
that
Terminals,
terminal
or arcs, does not
hazardous
attain
and
temperatures,
whose mains voltage
does not
Flameproof
d
If
enclosure
an
inside
l
'7
I
1 kV
exceed
occurs
explosion
the
enclosure
,
the housingwill
withstand
the
pressure
and the explosion will
not
be
outside
propagated
the enclosure)))
EN 60079-1
IEC 60079-1
Switchgear,
transformers
122 Practical
Marine
Pressurised
Electrical
p
Knowledge)
-
The
surrounded
::::7\037 - L pressurised
l
gas
switchgear
protective
0.5
(min.
a
by
Control
cabinets,
EN 60079-2
IEC 60079-2
source
ignition
is
enclosure
-
mbar)
cabinets
the surrounding
atmosphere cannot
enter
I ntrinsic
I
safety
I
l:::D
EN 60079-11
IEC 60079-11
the
limiting
By
Actuators,
sensors,
energy in the
the formation
circuit,
of
PROFIBUS
impermissibly
high
DP
RS 485-iS
temperatures, sparks,
or arcsis
Oil
0
immersion
prevented
Equipment
or
EN
equipment
parts
IEC 60079-6
switching
devices
in
immersed
are
Transformers
60079-6
oil and therefore
separated from
the
Ex atmosphere
Quarz
filling
(Sand
filling)
q
-
-
yv..,,\"[r-'..,r
\037
+\037
',-rti'''AY
. \037\037\037\037\\,-\037:*f:\037
,
..',\037i\037
., t:s.
\"\"'\037-.
i\037\037 \037fI\037\037\037'r\\
-'\037\037'11
- \037\037\037\037't
-:x
!.\037.\".
SI-<t
\037\037\037-v+.'\"
.....\037 ..-1\037\037\037\037
in granular
packing
material
Strip
IEC 60079-5
heaters,
capacitors
The
sand).
(eg
EN 60079-5
is
source
Ignition
buried
Ex atmosphere
surrounding the
housingcannot be
- --
m
Encapsulation
J
,....
J
--
,.
e-- -
by
By
encapsulation
the
arc
an
ignited
EN 60079-18
IEC 60079-18
of
source
ignition
in a
moulding, it
cannot
ignite the
--I- ---
Sensors,
switching
devices
Ex atmosphere
n
Type-n
Slightly
protection
ng)
(Non-sparki
I
- 'n'
I
types
PLCs
EN 60079-
simplified
application of
the other protection
stands
15/2/18/11
IEC6007915/2/18/11
for
'non-igniting'
radiation
Optical
measures
Suitable
op
prevent a hazardous
60079-28
Fibre
IEC
60079-28
conductors
optic
from
atmosphere
,&
EN
being ignited by optical
radiation.)
Table
6.5 - Classification
Exd
6.5
of explosion proof equipment)
Flameproof
Enclosure)
code
Exd (for group II), uses
Type 'd' protection,
a flameproof
enclosure
to contain
the electrical
apparatus. The internal
apparatus
may include
that become hot. Gas
parts that arc and surfaces
may
be
inside
conditions:)
the enclosure,
so it must
fulfil three
\302\267The
must be strong
internal explosion
enclosure
withstand
an
suffering
damage
\302\267the
from
flammable
\302\267the
must
enclosure
gases
external
being
enough to
without
prevent the flame and hot
transmitted to the external
atmosphere
surface
enclosure must
remain
temperature
below
of the
the ignition
temperature of the surrounding gas under all
operating
conditions.)))
Electrical Practice for
Special
The transmission
of flame
hot
and
from
gases
explosive products from
a flameproof enclosureis prevented
because
all joints, such as flanges, spigots, shafts
and
are
machined
achievea
to
bearings,
closely
gap
that
is less
than a defined maximum. The pressure
of an
internal
is then released through
explosion
the
small
the
between
machined faces, which
gap
cools
the gas sufficiently to prevent it from
igniting
any external flammable atmosphere.)
The maximum
factors:)
gap
permitted
the
The
. J
/
,
Armour
O-ring seal)
the width
.
the volume
6.4 - Exd
Figure
of the joint
.
of the enclosure (V).)
QUESTION)
battery room is fitted
In
Yes.
apparatus
gas
apparatus
gas from the batteries
for use in
designed
is hydrogen
IIC. The ignition
group
of hydrogen
is 560\302\260C and
classification
of the luminaire
that
so
the
surface
its
The cable entry
an
into
intrinsic
Generally,
This means
The
exceed
not
135\302\260,
is satisfactory.)
Exd enclosure
of the
design
must also
grades
of intrinsic
\302\267
Exia,
the
factor
of
a compound
of gland,
shown in Figure
6.4, has
that
forms
a
barrier
between
filling
\302\267 Exib,
the individual
conductors
flameproof
by using
means
to less than
30
or thermal
circuit will
depend
safety
are
the
50 mA.)
type of
on the
Two
grouping).
recognised:)
highest
category based on a safety
with two faults on the circuit)
1.5
type
and
prevents
entry
based
on a safety
factor of
1.5
with
fault on the circuit.)
of)
.)
Spigot end -.) '---)
*)
Adhesive
-- ---)
\"j()
O-ring)
Socket
Flange
Figure
of a
event
limiting
V and
gas expected to be present(gas
a certified Exd
be maintained
gland.This
voltage.
protection
conditions
circuit
temperature
will
temperature
the temperature
classification
and
fault.)
temperature
is T 4.
of a circuit
safety
current
circuit, no sparks
intrinsically-safe
occur
in operation, or even in the
an
effects
requires
Safety)
is achieved by
This limits the type
to circuits with
a relatively
low power, such as that
used
for measuring
or control.)
the
limiting
ANSWER)
The hazard
cable gland)
Intrinsic
Exi
The intrinsic
a flameproof
with
luminaire marked 'Exd IICT 4'. Is this luminaire
certified for use in the battery room?)
which
Cable)
(L)
6.6
A ship's
Cable clamp
clamp)
the apparatus is
with which
of gas
\037II-)
;')
use.)
for
entering
;vvvvo....)
im:
Compound
type
safe
enclosure
.. .. .. ..
.
I':.,,,
..\037
.. . . .\"\037
.-:.\".
\"...
. ..\037--.
\"..-.-:.
\037)
filter)
.
123)
Atmospheres
the cable.)
upon three
depends
Hazardous
6.3 - Exd flamepaths)
joint)
Sealing
ring)
I
I)
.'
J
-
I
/)
Spigot joint)
Screwed
joint)))
one
Practical
124
Marine Electrical
Knowledge)
measure
for intrinsically
safe
circuits
important
is their safe isolation from
safe
non-intrinsically
circuits. Safe electrical isolation is always
required,
with the exception
of safety barriers.Electric
An
.
(zener)
.
to limit
the maximum current
a set of shunt-connected
the
maximum
within
the
All
components
with
clearly
the
area
hazardous
the
into
used for limiting
as well
diodes,
voltage
as other semi-conductor components,are
considered
to
be fallible
and must be safeguarded
redundant
Wire wound or sheet
by
components.
resistorsfor current limitation are considered to be
infallible
components
(as they have high
resistivity
in the event of a fault),
so only one component
is
the maximum current through
diodes
a set of resistors
Zener
zener
voltage
hazardous
appearing
area.)
diodes
to limit
on the circuit
marked
sealed
into a compact package
terminals
at each end of the
in
6.6
are
barrier.)
sufficient.)
The
to limit
fuse
A
.
barrier comprises:)
(or zener)
shunt
for Zone O.)
recommended
is generally
isolation
A safety
of a zener
purpose
and currents
in
the
barrier is to
hazardous
area
limit
The
voltages
circuit
Figure
occur on the circuit.)
in
of a high
event
the
a single-channel
action
preventive
shows
zener barrier.It illustrates
when faults
the
voltage
being
accidentally
applied to the non-hazardousterminals.)
barrier is required for each Exi circuit
must
be fitted outside
the hazardous
area
they
A separate
and
(see Figure 6.5).)
.
Hazardous/ocauon
The
zener
bias,
has
reverse
diode, when connected with
an approximately constant voltage across)
\".-)
terminals)
Binary sensor
Hazardous location)
::)
\\
0)
.:)
(\037\037
,'0In
.
-I
I-
:s)
II)
. .
equipment
Non-hazardous area)
IS barrier)
,
\037--')
Monitoring
. i)
Non-hazardouslocauon
t
terminals)
o)
,)
Positive
single-channel
zener barrier with
.I
.
..:..\037.-----)
negative
\037'.1 :'
..},\\.
\".\037.\"
,:\037
.
ground
for digital sensor)
\037..\037)
\037\".')
,:
,..:,
',.\"..' ':,
\037
\".).,J:.
,:..'\"}'
-\037,'
,.)
..
,
.-'-.-,,].l.\037Jj
'., +- 'aa:II.'--\037 \037
\037
. .)
'\"
.
\".
\037:jt\"I.\037.('Hj\037 'H\037.
;\037t: \037lt: \037\037I;:
\037\037I:
.',
!.l' - ;..:ff.
!H\037
' tto;)f,o,
't.t .<:
I
\037I,: \037\037I,:
.L.:
\\.QS;I ,..
'Sl\037':liEf)
\
\"
\\)
Figure
6.5 - Exi barrier construction)
.
X:))
....:\"\
')))
I,IJ1r.,
Electrical
Special
R)
r)
Practice
for Hazardous Atmospheres 125)
F)
1)
3)
mA)
area
Hazardous
Safe
Z1)
termmals)
area
terminals)
4)
o
+ ve
30V)
r
Fuse
Blows
o
- ve
,-------,,
U
I
I
I
I
I
\\
z
\"
+ ve)
diode characteristic)
2)
6.6 - Exi
Figure
barrier
external
of the size of
the instrumentation
current
an accidental
to
input
the
high
voltages
the maximum
appearing
voltage
area wiring.
While
the
current
level
is designed
now
isolates
the circuit
zeners
them.)
sheath.)
In normal
has
a supply
appears
voltage
the diodes
to their U z rating.
barrier,
the
safe
The metallic cable screens of intrinsically
circuits should be earthed, at the powersupply
end
only, to prevent circulating currents within
flow.
circuit
voltage lower than the U z voltage rating
zener diodes so no current flows
through
When
fault)
operation)
it, irrespective
operation,
due to an
Overvoltage
Example:
of
at the
and
Power
separately identified,
This then limits
with a distinctive
to blow the fuse that
in the
to maintain
safety
of a short-circuit on the hazardous
the in-line resistors
equipment,
wiring
will limit the size of fault current
the
barrier
within
while the fuse blows.Two or three zener resistor
to provide
a barrier
combinations are used within
event
area
or
backup voltage anchors while
After
clearing
must
be
alterations
certified
the
fuse
is blowing.)
the complete zener barrier
No
with an identical unit.
a fault,
replaced
runs
should be
or by
using
blue
for
colour (typically
Increased
Exe
6.7
cables
Exi).)
to the original are allowed as this
Ex safety device.)
is a
of
switch
relay,
of
motors
of
surface
In
addition,
circuits on board ships
safe
Cables for intrinsically
should be separatedfrom power cables and the
crossing over of such cables should be at 90\302\260.This
is to minimise electromagnetic interference from
safe
cables affecting the intrinsically
the
power
open
contacts,
Safety)
Exe is based
as
designated
containment
and on the close control
generators,
temperatures.)
the
on the
at locations such as
sparking
or slip rings
the commutators
and
of the equipment is to
construction
developing.
high standard to prevent faults
insulation
is used, creepage distances
a very
Extra
between bareterminals
made
are
longer
and
due
against
damage
special enclosures to protect
to entry of moisture and mechanicaldamageare
also
(see
specified
circuits.)
cable
on the hazardous
are conducting, the
Equipment
the
ie
the
by labels
safe
intrinsically
conduct to clamp
area.)
hazardous
In
Voltage)
0
\037J
Zener
------\037
4)
their
- ve)
Reverse bias
1
3)
0
\037J
0.6 V
R
bias
Forward
Up to
2)
Figure
6.7).)
and to
is made to withstand
impact
of
solids
and
liquids. Applications
prevent ingress
and
luminaires
include cage-rotor induction
motors,
metal
Exe
cable
boxes.
connection
glands,
Special
The enclosure
or plastic,
are used with
Exe
apparatus.)))
126
Practical Marine Electrical Knowledge)
Clearance)
Creepage)
...........
\037...
..................
.
..
.
..
-.:
'..-)
across
surface
of insulating
material)
Distance
-
and clearance distances)
Figure
6.7
6.8
Exn Non-Sparking)
to
Similar
Creepage
Exe,
equipmentthat
surfaces that
Exm
6.10
the designation
Exn applies to
has
no arcing contacts
or hot
could
cause
ignition.)
works
This
Exn
are
requirements
Exe, and designs are very
less
stringent
close
to that
than for
of normal
Encapsulation)
the equipment in organic
the potentially explosive atmosphere
by enclosing
resins
to keep
away
from
of ignition.
source
the
under normal
fault
and
The
encapsulation
from increased temperature
protection
provides
The
in air)
Distance
conditions.)
electrical apparatus.)
6.11
The main
is extra
consideration
connections
locking of terminal
electric sparkingor flashover.)
6.9
care to ensure
to avoid any risk of
Pressurised
Exp
Apparatus)
inert gas is suppliedto the
above
equipment
slightly
atmospheric pressure
to prevent entry of the external flammable gas.
Clean, dry
air
or an
This method is sometimesused for
enclosures
instrumentation
and
motors
,
lighting.)
pressurisation
the
internal
or by continuous
requires
system
electrical
of pressure which,
in turn,
before
enclosed electricalcircuits.)
also
be
for a reduction
will switch off the
signalling
Systems
Operating
in
Hazardous Areas)
The
relative
EN
60079-14.)
regulations
are specified
in
Cable systems are mainly
used
in Europe
for
electrical installations. For this, high quality
cables
are laid unprotected. It is only in areas in which
mechanical
could be expected that they
damage
are laid in conduits
that are open at both ends.)
for electrical
used
are
systems
systems in hazardous
equipment is permitted to
and trip
Electrical
areas:)
circulation. A
a purge flow
must
operate. The pressurisedenclosure
fitted with alarm
and
Three installation
in Figure 6.8 show that
the
diagrams
internal
be
maintained
pressure
may
leakage
by
The
compensation
Installing
Cable
In
the
indirect
system with
of indirect entry,
case
are conducted via
cable
cable
the
glands
input
and
cables
lines
into a connection
chamber in the type of protection 'increased safety'
and connectedto the terminals
also
provided
in 'increased
safety'. From here, the individual
wires
are conducted
via flameproof bushings into
the
enclosure.
The cable bushings
flameproof
are installed
that,
by
by
contrast
manufacturer,
with direct entry,
of the factory-wired flameproof
made. The terminals also have
'increased safety'.)))
result
with the
the
test
a routine
enclosure
the
can
protection
be
type
cu
cu
\037
cu
\037
cu
CI)
\037
\037
cu
CI)
of
gas
t
t
0
-e
cu
N
cu
Protective
t
.
J:
inlet
gas
Leakage
protective
for Hazardous Atmospheres 127)
Practice
Electrical
Special
.
.
valve
Outlet
Pressurised
arrester
Spark
(shut)
enclosure
with
leakage
compensation
Air
fan
supply
.
.
\037
.
J
J
cu
cu
\037
cu
\037
cu
CI)
\037
\037
cu
CI)
0
-e
gas
Leakage
of
gas
t
t
.
J:
inlet
\037
.
Pressurised
to restnct
Choke
exit of protective gas
Sparkarrester
enclosure
.
.
Air
supply
fan
Circulation
system
.
.
J
J
Figure
6.8 - Exp
(pressurised) enclosure arrangements)
Cable
system
with
.
cables
are fed
into
the
closed
as
a conduit
system.)
Work on intrinsically
in
hazardous
the most important
safety
measures
are:)
the safety
Some of
systems
in
hazardous
safe
circuits
is a
danger
.
or shortgrounding
if there
is no
permissible
areas,
is only
circuiting
of explosion
of all work carried out in hazardous
there
must be no possibilityof ignitable
areas,
or
excessively hot surfaces occurring
sparks
cause
an explosion if in conjunction
that
may
in
the
case
with a potentially
to maintain
Regular servicing is required
areas.
of electrical systems in hazardous
on live electrical
work
permissible exception
metal
to
is connected
piping as single cores. The piping
with
a
the housing using glands and is provided
The entire piping system
seal at every inlet
point.
The piping system is also
in design.
is flameproof
known
areas.
.
Conduitsystems
out
Carrying
and equipmentis prohibited
The cables are run direct into the device installation
certified
for this
areas. Only cable glandsspecially
be
used.)
can
purpose
electrical
gas outlet
J)
cable input
direct
Protective
creates
Choke
overpressure in the
enclosure
.
.
The
gas outlet
Protective
J)
protective
t
cu
N
cu
Protective
(open for purge)
explosive atmosphere.)))
128 Practical
Electrical
Marine
Rules
Class
Additional
6.12
Knowledge)
the
for Tankers)
Only
of a tanker carrying
Society
combustible gases and vapours
will have a set of
additional
It is important to ensure that
rules.
the
vessel
remains
within Class by giving
these
rules
Classification
The
close review and consideration.The rules will
such as:)
aspects
.
Powersupply
\302\267cable
cover
systems
installation
\302\267electrical
areas and
in hazardous
equipment
extended hazardousareas)
\302\267 motors)
\302\267
control
signalling,
measuring,
\302\267
\302\267active
cathodic
in
Testing
Areas)
Hazardous
tested
be
must
and
apparatus
periodically
defined testing routine with
Insulation
earth
the
circuits
associated
in
a
results.)
with
accordance
test
recorded
resistance, earth loop resistanceand
resistance
tests must be
continuity
last
two
in relation
to the setting or rating
made,
devices
protective
and its circuitry.)
It is
with
the
in such
made
and insulation used in intrinsically
and circuits are damaged by excess
area,
certified
electrical equipment is
may insulation resistance
a 500 V DC tester of
using
safe
intrinsically
(Exi) design.)
The testing and maintenanceof flameproof
or
safe equipment should be entrusted
intrinsically
to competent
persons who have received
only
in the special
instruction
involved.)
techniques
The body material
of instruments
and tools required
for maintenance purposes should
be designed
so
that they will not make a hot spark when dropped.)
of
all intrinsically
Where
such
should
be
of
testing
after
circuit
the
safe
test
No apparatus
effective
and
switch)
live
again
one
Apparatus)
Exd-protected
tests are
----)
devices
. ..
apparatus
.'.)
voltages.)
should be openedin a dangerous
been made dead (no longer live)
measures
(eg locking-off the isolating
been taken to prevent its being made
have
inadvertently.)
. '\\)
.\037)
-)
.... - .
\037')
for the purpose of electrical
it is
testing,
before
the
necessary to restore the powersupply
is reassembled, tests should be made
apparatus
a suitable
using
gas detector and continued during)
Where,
Figure 6.9 - Exd
(flameproof)
minute
of
Maintenance
it has
until
may
of a
are used, the test leads
throughout and, on
the
test, they should not be detached
has been discharged through
the
(leave the tester for
the test is finished).)
the
risk
connected
instrument
6.14
a
instruments
firmly
..)
area
safe
apparatus
that insulation resistance
a way that the safety
important
NOT
associated
the
testing be carriedout,
until
electrical
or the
from
completion of
All
safe,
of small inductanceor capacitance,but
arise when such energy storing
properties
circuit have an appreciablevalue.)
systems.)
protection
Electrical
6.13
ballast systems
and
cargo
integrated
otherwise
removed
area can be made gas free,
hazardous
if the
do
gases
instruments should be so small
that
they do not
tester
has a
produce hot sparks. An insulation
and
drooping characteristic to prevent high currents
safe
when
may be intrinsically
applied to circuits
ventilation
and
or
combustible
that
the explosivelimit.)
The energy output
and
intercommunication circuits
\302\267fans
to ensure
operation
not approach
motor
construction)))
Special Electrical Practicefor
The inspection and maintenance of Exd
enclosures
for luminaires, switches,
(flameproof)
etc requires
buttons,
push
boxes,
junction
meticulous care.)
The following
example
and maintenancepoints
to the inspection
to a flameproof
applied
as
luminaire:)
If
When
enclosure
the
strength.
To
greased
ensure
ascertain the extent of corrosion,
surface
only
the
paintwork
be
should
is deteriorating,
to prevent
repainted
the enclosure
corrosion.)
further
.
Bolts
bolts
distort
Make
sure
are
there
that
This is particularly
important
no missing bolts.
on flameproof
tensile
as originals
strength
.
(usually high
Ensure all mountings
severe
are
are secure. Corrosionand
on ships and can cause
the flamepath for signs of
If
the
needs
flamepath
or
corrosion
cleaning,
this should
be done with a non-metallic
and/or a
scraper
suitable non-corrosivecleaningfluid.)
Cement
the cement
Examine
assemblies
both
is eroded,
used around lamp-glass
and
inside
If
deterioration
a completenew
fitted.)
outside.
If
softened or damaged in any
should be sought from
repair.
.
the
of the
lamp-glass
manufacturer
cement
assembly
the
cement
way,
advice
regarding
has occurred,
should
a
as this can
excessive
cause
flamepaths,
the
is installed
luminaire
be
any build-up
removed
as
in
stress
with
accordance
of dust on the luminaire
it
cause
can
as a corrosiveagent.)
Before
Flamepaths
pitting.
are not over-tightened
of the installation,
particularly
classification
of the area if it is hazardous,
that
the
correct
rating of lamp is fitted
failure.)
Examine
to
from
that can
requirements
Mountings
premature
taken
and dusts
steel).)
vibration
be
are free
on lamp-glasses or distort weather-proofing
if fitted,
gaskets,
allowing the ingress of liquids
luminaires because a missingbolt will invalidate
the certification. Replacement bolts must be of
equivalent
holes
blind-tapped
accumulated dirt or excessive
grease
or
prevent the correct closureof flamepaths
cause damage to the tapped components.Fit
new lamp of the correct rating
remove
dirt, loose
with a wire brush. If
corrosion
and
paint
that
you must
and threaded componentsare
with an approved
form of non-
All flamepaths
setting siliconegrease.Caremust
Corrosion
reduce
Exd enclosure,
an
re-assembling
the lamp-glass.)
Clean
fitted.
be
ensu re that:)
.
will
new lamp-glass
a complete,
or broken,
cracked
lightly
This
129)
Atmospheres
Lamp-glass
assembly should
is a guide
Hazardous
attempting
for
any
overhaul instructions given
particular
by the
and
is
overheating
any maintenance
equipment,check
the
the
and act
work on Exd
and
inspection
manufacturer.)))
Chapter
Seven
Periodic
Survey
The
periodic
following
Requirements)
are carried out on
surveys
installations
Electrical
{--
.
.
.
Annual
{--
{--
for the hull
Regulation
Main
Extendedannual
the
or third
second
42-1
Regulation
annual
on board will
{--
survey.)
be
Emergency source of
43
Regulation
electrical
44
{-- Regulation
Starting arrangements
Precautions
45)
Regulation
and
ship.)
Chapter
and stability,
divided into
machinery
five
within
subdivision
which is
electrical,
reliability and integrity
including
the
auxiliary
systems.)
Part
A
General
{--
Part
B
Sub-division
{--
Part
C
Machinery
and
strength,
function,
parts
of the ship
power
generation
propulsion,
of Classification
Association
International
is a
a forum
technical
organisation that
for 13 major Classification
Societies(Class)to discuss,
and
research
standards
and
adopt
for maritime safety.)
on
services
board
ship
specified
organisations.)
stability
installations
Part
D
Electrical
installations
{--
Part
E)
Additional
requirements
spaces.)
the
essential
must also meet the minimum
standards
by various national and international
{--
periodically
of
Electrical equipmentand
parts:)
{--
of
hazards
Societies)
ClassificationSocietiesverify
provides
Structure,
and
against shock,
other
Classification
Societies(lACS)
11-1 'Construction
sets
electrical origin.)
The
SOLAS)
SOlAS containselectricalregulations
ships
for
generator
emergency
{--
in cargo
power
subject
to mandatory periodic type approval
as prescribed
under the regulations for the Classificationof the
7.1
passenger
ships
7.2
equipment
ro-ro
for
lighting
renewal
electrical
of
emergency
Supplementary
surveys are carried out for the ship's
hull
and
machinery,
including the electrical plant.
will be surveyed at the
special
Any
equipment
intervals
indicated
of the hull.)
by the Classification
The
systems
source
Emergency
fire
Class
of electrical
source
ships
where
to as
referred
surveys,
and,
intermediate surveys, fall due approximately
2.5 years after commissioning, at each class
renewal
and
ships, also be
.may, for seagoing
at
42
Regulation
the
and
{--
including the electrical plant
for special equipment.)
carriedout
General
41
into:)
electrical power in passenger
are conducted
surveys
machinery,
applicable,
40
power and lighting
Class renewal survey.)
Annual
Regulation
iate
I ntermed
D) is sub-divided
(Part
merchant vessels:)
unattended
for
machinery
The standards
specified by organisations
when the ship is designed,built, approved
classified
by the classification society.)
The shipownerand
operating
staff
must
are
maintain
the vessel and its electricalinstallation
to the
of the Classification Society
requirements
throughout
the
ship's
lifetime.)))
met
and
Marine Electrical
132
Practical
7.3
Main
Knowledge)
Electrical
Survey
QUESTION)
Items)
Would
an IR
acceptable
The following
ships:)
.
items
survey
main
and
generator?)
apply to all
generally
.
switchboards
.
cables
.
insulation
resistance
.
motors
and starters
.
emergency
.
parts
and
equipment
of steering
gear
Remember to disconnect
indicators.)
instrument connections and generator heater
supplies
when
For unattended
a survey
of
detection
is also
the
machinery space (UMS)operation,
alarms, controls and fire
associated
required.)
For tankers/gas carriers and
each
all AVR
for
testing
other
ships
survey
docking
and annual
su rvey.)
IR.)
to the contact surface of any
or slip rings is required. The contact
surfaces must be smooth and concentric without
of pitting or deep grooves. Carbon
signs
any
attention
Special
must
brushes
the correct spring
length, maintained at
be of adequate
and
pressure
onto its rotating
properly
or slip
commutator
to remove any
dust
carbon
excess
the brush gear and around rotor
Governors)
The surveyor will require
that main and emergency
to controls
generators are clean,respondcorrectly
and load changes and show stableoperation
when
to run in
with
parallel
other
generators.)
Generator windings on the stator and rotor must
be free of dust, oil and moisture (see Figure7.1).
A visual
check
will be made for any obvious
deterioration, abrasionor crackingof the
the end winding
around
An
test
insulation
phase
windings
coils
to earth
on the
the
proper
with
correct
and between stator
(if the neutral
point can be
at the
terminal
box) should be carried
machine
is still hot after running on
the
while
load (see Figure 7.2).)
The rotor
diodes
diodes
(PIV)
must
circuits
value, taking
care
of a brushless
usually
rating.)
also
have
be tested for insulation
out the rotating
shaft
excitation system as the
a low peak inverse voltage
vicinity
of
values
frequency and current
generator control panel. Governor
and its response
to sudden load changes
be within
the declared specification for the
droop
must
prime mover/generatorcombination.
load sharing
of kW
and
kVAr
factor) between two
or
more
as
well as
parallel,
generator's
Automatic
start
load of the
standby
blackout
of
Stability
(or load current/power
generators
running in
the reverse powertrip of each
circuit breaker, must be demonstrated.)
functioning
generator
and
switching
in
must be shown in action
under
of
event
the
for all generator
sets.)
It
is
practice
regular
to carry out all the tests
relatedto the electricalinstallations
prior to the surveyor's visit.
to short
the
voltage,
disconnected
out
in
coils.)
on the
indicated
insulation
stator.)
contoured
ring. Be sure
running tests, on load, should confirm
of governor and AVR controls
operation
Generator
and
Generators
required
equipment,
commutator
flammable cargo, an additional
transporting
survey
of all electrical equipment in hazardous
areas
is
carried out during
MO is generally
1.5
0.1 MO should
specified
equipment,
be acceptable in special
cases.
most
However,
1
would
insist
on
at
least
ie
kO/volt,
surveyors
440 kO, say, 0.5 MO as a reasonable
minimum
value for a 440 V generator.
For HV equipment,
the usual recommendedminimum
IR level
is (kV + 1) MO, eg for a 6.6 kV motor, the
IR would
be 7.6 MO.)
acceptable minimum
fittings
power
light
of
new
for
circuit breakers
navigation
a minimum
Although
governors
.
7.4
be
ANSWER)
Generators
.
MO to earth
of 0.5
result
test
for a 440 V
This
correct operation and allowstime
problems
that
may
occur.)))
on
board
will ensure
their
resolve
any
to
Periodic
- '::::::--'\"
.....::;,
,
-,.')
Survey Requirements
133)
.)
\037)
\"'\\)
...,
\037
.....\"
\".)
\
,\"
, '.,'.A-)
,\
.
':.<\"\037))
---\037)
o)
....)
\037.',
.
-')
,
:,'.
l
','
.'.- :'!\\.''-:'
\037,)
,)
--'
.'..-')
.,-)
,
,-)
' ,
,
\"
I)
,
: \037.I
\\)
\302\245)
'. \037.}\037\\:.\037\037\037\037\037
..)
\" ,..\037.:...
\037;.'- .)
.,\\:
. .r..
'J'\" -\".
.,:\")i\"
-. .. -;,...)
'.. r\"__)
'.:.:::/::\037\037;::\\.')
;:-j\037)
! \"i')
-..::.
.)
\0377.;) , \".,
.. :-:;.
,-':)
\"
\\,'-)
\037,
1
.\".-\
\
.\
.0 \037\"'\037-'\037'''....''
.\":\"\037
.\037.'''..\037
, ......<
. . .\
.
,'; ..\037
.'\037.
. tt JrJ;'!
.
tJ
\"'; \037
f\037',)
\
\037
\037)
.,\037)
..)
. I. ..,.)
.
\037.
\037. :
i\037\037
':-)
'\037\037f::
\037/): _.t-\037.-.., \037--.....)
t,.'.;\037.')
(b))
.;'J)
. .\\'
'd.i/l.
\
\037
, 1/ ')
(a))
Figure
7.1 - Generator's excitation
b) CAT
oil
generator
and dust))
component
system
a) SE generatorexcitation
view
condition
and oil free)
and
heaters
space
(clean
components
at the stator winding
(unacceptable
,)
.
.)
0
0
.If
111'; ,
I w
..'\037.)\\\\:II
'\",,//,,
\037
\\,\\\"7
4
Ii) :
Me
'o-t\037)
IES\037) NITEST)
..\" 1\" ( r \037..j)
.....v.:
, . .........6.@CEIl '
: =\302\27300\"-6
0 0
\037\\ \037l
' \\
.'
.
.)
l1J.o\037 :-0:')
-, '\037)
.)
.)
'0
O! 0
'-Itr
o,< \037:O 0 'I.\\.
\037', '6\037\"\"
n :r.r:
.6.@:CE1l::
... ')
:0
3S\037:_@', .)
,\037XI
0::::---(:)
.\037)
l')
Figure 7.2 - Induction
motor's
insulation
\"1
.. \\.\\,\\jillii\",,//..
\037,
\\,\037.\\\037
l
Ii) i
Me
-o-\\t'\"\037)
\037Tb ,:UN EST'
-.;;;.;-
resistance
(IR) test)))
j)
condition
due
to covering
of
Marine Electrical
Practical
134
Breakers)
Circuit
7.5
Knowledge)
3 x 440V, 60Hz EMERGENCY
Em. Gen.
visual
examination
emergency
and
A
breakers
of circuit
usually
tests. The surveyor will
operational
for overload current and short-circuit
settings.
aligned.
correctly
good
condition
tight.
The
internal
All
precede
check
ACB
\037ISI
I ; I I I 1,Ii
wiring
be in
should
\037\037
-.
and
debris
.\037
..
\037
\037 (;;C\037
--,.... j
-.
-.
.
.
.
I I
I
I
I
I
I I ; I I I ..
-.
-.
.
all mechanical
surveyor
may request that
are checked for any signs of wear or
linkages
stress.)
f\302\2431
.. ..I.. _
end connections must be
and the
.
.. -ISJISI
L!. :.; .\037._!..
..\\
\037
\037
I
.
ISJ IS1E1
protection
3 x 220V consumers
h Z20V
I
.
\"
overheating.)
must be clean, free of
chutes
Arc
3 x 440Vconsumers
h .....
I
I
c.--..
be inspected for signs of
should
also
at the rear of the
Main terminals
main,
Em.\037
boards will
section
in
SWITCHBOARD
I 111 11 11 .
I ; Ii I Ii I Ii
1 , 1 11 , 1 , 1,
I ; I Ii I I I
.
\037
\"\037'-'\"
.
---: \037
If 1 -:- -:-\037--_
.
[; I (f f ?-\"';
J Ij ,,-.-1
>J . I: .
jf n
\"
,
''',II',l1J
JIII\037'\037\037'f1J
\"\037'
.IJII\"ml!'f.\
.
: 'c_ \"-'
I. /:).,
ili
.;:!\037t\0371)
.'
i
-\037
. If ,. r
(a)
I
.
I
,f
.
rf;\037\037\037
fl\037. \037\037f\037\037;\037')
N..,.,\"
I
..
.....
\"
o
\037)
..
ItIl..
..
_u)
;:t'.::
.. \037r\037
,
;-t..
1 <
_01 _0-
\037\037
!\037.\037
j\037cI)
0,
I
..
It.
I
I r:
I:
\"1:
'';'-- r',-.
I:
1'[
!oC
:.,r.
II:
Ll:
he
'it:
II:
II:
1:1:
. 0
..
[]
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Ii:D)
I
\\)
.
.
Q
\037
I!!I
m\037]
\"
11\"
':\037
- '.
Ie 1 i 3 i
...:Tr
,,[
..I-\037t;:
I.'-('e
\037
I'f-.,.,
'-
:; ..
-
.
I
\037';;
..
:':
:
..
.. .. '
..
to
Figure
7.3 - Generator's
1'0;
I
J
TC'
,I t:
1C
... . '1:1:
. -'........-.
\037
\"'tt-o
-
ACB)
.
.) .
.,
:
,,'
-- :
f.OJ <
\037
I'
-...
.....
\037 \"
, -.
CII
:t)
:..
f\037
..::
,\037\037:
;..1 .
r
'.
'.
!
.
-
,
While checking the generator's circuit
breaker,
the surveyor
may ask to see its closingand trip
; -a....
its
in
isolated
is withdrawn.
hand
Emergency
charging
(if fitted) of the closing
will
be
tested.
Correct
spring
operation of the
mechanicalindicators
to show
whether
the breaker
off
shuttered
when
procedures
are generally
related to
Class
vessels.
They
intermediate
and
it
is
for
the
to
surveys. However,
surveyor
decide which
Similar
test
during
the
crew.)
particular
procedures
regular
checks
operations
he
will
test.)
should be scheduled
carried out by
the
engine
\037
\037'\"
.
. -.-.
--
,.
\\
--\037.
\037
\"-
(
the breaker
surveys carriedout for newbuild
are rarely carriedout for annual,
II i
.i
--
'\"
'\\\"',
,
1
.
.\037
\037
\":
'\037I-
\037\037
'-\", ...'
-',
\"'<:,'\"
......
,-
\037'
-\" '
_.
-,p I
,,:
\037.\037\037
\037
\037--
/.
.-
(\"-1
- --
-.
---- ,
\037-'
' :
I
\037-
..
\037
\037
'I
,
\"?'
-. \"
test
I
(b)
is open, closedorisolatedis required.)
These
',
i
I
,\037
position must be demonstratedto be freemoving
and
the fixed main terminals must be seen to
be
:
Ii
II.
Ililutlll'
operations
position (ie not
connected in circuit).
The racking
mechanism for
the
breaker
from
the
service
to the isolated
moving
while
I
:-..
'''I
.1
I
..,.
..\\
.
\\\\
......
,-.
- \037 .....
(c))
Figure 7.4 - Emergencyswitchboard
arrangements
a) Panel
view
at ESB panel's
b) Internal
c) Busbarsand
main
connections'
components
condition
(unacceptable due to accumulateddirt
all internal components))))
on
Periodic Survey Requirements 135)
mechanism and
and time delay
have
to be demonstrated
to the surveyor's
may
An overcurrent
satisfaction.
trip for a generator
breakeris typically
set
for 130% of FLC, with
a
The
release
undervoltage
overcurrent trip
for level
settings
time delay of 3 seconds, but this
suit the thermal capacity of the generator
has
typical
coordinated with the overall
the power system.)
be
scheme for
protection
bonded with
the
overcurrent
and time delay settings
on the breaker can beseentobe correctly
adjusted
to the desired values, only a proper current
test will prove these settings against the
injection
Although
or (more
injection)
(primary
usually)
What is the reason for
earthing
secondary winding
aCT?)
and
One of the
main
Fittings)
requirements
survey
for any
board
switchboard, section boardor distribution
is that they are clean. This includesall internal
surfaces
as well as the external panel surfaces,
and control switches. A thorough
on
the
inside of the main switchboard
job
be safely
carried out when the board is
faces
instrument
cleaning
can
only
dead
completely
(all generators
stopped
movers lockedoff).)
All
main
the
tightness
are
junction
heat
signs at a connection
up. Overheating
testing
camera
due to a loose joint.
Direct
probably
on load with an infrared
thermal
is a useful
for locating
technique
Busbar supports will be examined
tracking and damage to the insulation
All internal
hot-spots.)
for surface
on the earth fault
current transformer
the
frame
secondary
(CT),
isolator and fuse holder contacts must
be
for any mechanical wear or damage due
on
moving
contacts
is usually recommended.)
will
Operational tests on a main switchboard
on the synchronising controlsand generator
protection
relays, such as reverse powerand
load shedding
preferential
trips. Typical reverse
focus
powertrip
settings
may
range
between
5-15%
of the generatorpower rating,
with
a time delay
of 0.5-2.5 seconds for a diesel drive. Equivalent
settings for a turbo
generator
may be 2-5% and
5 seconds.)
Time
delay
settings
must
allow for the operating
winches
practiceon the ship.Forexample,
cargo
and cranes
back
into the
may, at times, feed power
such
supply network. Under light load conditions,
feedback
cause
a
regenerative
may
generatorto
on
reverse
if
its
time
trip
power
delay was set too
short.)
material.
bar must be securely
of the board and the
of each
terminal
and the metal cases of)
earth
switchboard
bondedto both
ship's hull. One
monitor.)
to overheatingor arcing at the contacts.A slight
smear
of a proprietary electrical contact lubricant
7 .7
Cables)
test on a main cable
of cables and their installation
on a close visual
examination.
external damage of a cable's
outer sheath and wire or basket-weavearmouring
The cable must be adequatelysupported)))
(if fitted).
Apart
from
an
the survey
is largely based
for any
Inspect
run,
The main
to full
which
switchboard
panels
wiring
must be securely fixed.Cableentriesat the bottom
should be sealed with a nonof the switchboard
material to exclude dirt and act as a
flammable
fire stop.)
the
within
of the
connections
the boards should be checked for
the dead period of a major
internal
during
throughout
clean
and auxiliary
busbar
and prime
raised
earth,
be
above
Feeder
Switchboards
end
primary
voltage,
eg 440 V
could damage the secondary
insulation
and
create
a serious risk to personnel.
one
end
of
the CT, the circuit
is
By earthing
to zero volts. In addition,
anchored
the earth
connection will allow such a fault to be detected
can
checked
7.6
one
If insulation
between
primary and secondary
windings breaks down, the secondary circuit
relay (secondary
injection). This is
a specialist
task for an outside contractor.)
generally
of
ANSWER)
the
through
panel doors should be
to the main
switchboard
strap
QUESTION
test, the
circuit breaker is isolatedfrom the busbar and a set
of calibratedcurrentsfrom a current injection set
the closed
circuit breaker
are fed directly
through
overcurrent
earth
an
frame.)
In this
lIt characteristics.
manufacturer's
should be wired to the
relays,
Hinged
bar.
earth
main
to
and
and
instruments
IR (megger)
136
Practical
Marine Electrical
along
horizontal
and vertical
Knowledge)
runs
by
cable
suitable
QUESTION)
clips or ties.)
cables
Where
be
must
they
boxes
stopper
EPR or butyl
good electrical
mechanically
strong or
resistant to oil. This is why a sheath of PCP
or
is stronger
and has greater oil
(which
and fire resistance)
is fitted around the inner
insulators
correctly
glanded or pass through
that prevent the passage of fire
Common
shipboard cable insulations used include
with
or butyl
rubber)
propylene
(ethylene
is sheathed
PCP
either
rubber
(polychloroprene
subjected to oil vapour,
the cableendsto prevent
insulation.
inspected
repeatedlydraggedand
in doubt,
If
chafed,
its safety.
reducing
flexible cables.)
replace
of the
deterioration
Check that
be
normal
In
to light fittings, power tools, etc
for mechanical
damage.
a flexible cable may be
operation,
cables
Flexible
should
terminations
may be
it is usual to tape or sleeve
cable
EPR/butyl
not
are
insulation.)
or CSP (chlorosulphonated polyethelene).)
Where
are
rubber
but
CSP
compartments.)
EPR
PCP
and
ANSWER)
between
that
of EPR or butyl
functions
or CSP?)
fire check bulkheads,
though
pass
the
are
What
Where cable runs along an open deck have
for
expansion loops,these must be examined
abrasion and wear.)
is secure.)
taping
-, .)
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'r'
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,.)
f)
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...)
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\
,\",'i.)
\\
\037.,)
'.\",
feeder's
condition (cable rail has
a) Crane power supply
deteriorated
to an unacceptable condition
due to corrosion))
\\\\
w\\.' .
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i
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.'.' \037..........
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.
.
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))
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<:.
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.)
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d
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. '..... .7,'
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t
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f)
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---)
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4.)
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-,
dust))
7.5 - Cable
inspection)
.,\037\037)
'. .1
.\037)
.......)
switchboard panel's condition
frame's
Emergency
(panel
condition has deteriorated
due to extended corrosion; cables
the switchboard
covered
with
throughout
panels are heavily
Figure
\037...<' .
;..., ,
I)
\037.)
./J I
,\037)
c)
'.
.. .)
.---)
\"
\\\037
.
. '\\f
.\037:\037I
,-\"'\\-r-)
-J
\",,\\.'
insulation
-,}-\037)
.\037- .)
-
Main cable rail at the upper floor in the engine room (outer
sleeves
have been damaged by overheating))
b)
..
\\
.
.)
d) An example of the volume
a ship's repair)))
during
of
damaged
cables
replaced
Periodic
A
earthing braid/wire is
of all electrical motors
or flexible
strap
copper
usedto
frame
steel
the
bond
and other equipmentto the
ship's
hull.)
ammeter at the starter) should
bond required?)
an earth
is such
Why
earth
an
a loose internal
strap,
the frame, causing it to
touch
may
at mains voltage with
of
live
starter
equipment
to
the
checks
weather conditions
(hot,
comments relevant to the test
(eg machine hot or cold).)
An
of an IR log and
example
is shown
a motor
in
Figure
Associated Equipment)
1.10.)
a set of past results showing the insulation history
of such machines may be requested.)
This
section
emergencygenerator
is covered
and
Governors).)
The
emergency
manually
under
generator
selected
and
frame
the IR test
through
checking
test
box will
reveal
motor
is covered
with
dirt,
damaged
or
be
suspected
if
oil or
the initiation
of starting equipment
automatically,
and operation
The surveyor
on motors with
watertight
will
be
more
drip-proof,
enclosures.)
external
is
atmosphere.
likely to concentrate
and deck
weatherproof
supplies
taken
from the
emergency
see
if they
are
to
switchboard should be checked
and
rated
current
their
frequency
voltage,
receiving
when powered from the emergencygenerator.)
rust.)
induction
Totally enclosed, fan ventilated (TEFV)
motors
require little attention as their windings
are protectedagainstthe
Electrical
any
missing parts. General neglectwill
the
must be started,
results list,
on
may ask to witness a repeat
A visual examination of a motor
motors.
terminal
power
battery
while
or
observed.)
a surveyor
of the
of the emergencygenerator
the heading of Generators
(inspection
equipment
itself
Starters)
the operation
surveys
and/or
sequence
After
motor
Power and
7.1 0 Emergency
its graphical trend for
gears,
and
the
and
conditions
generators
Motors
lamps
running,
eg
rati ng.)
motors
and
For essential items, such as
the
to propulsion, mooring and cargo
related
will be more interested in the IR trend, so
surveyor
7 .9
condition,
the ship's/manufacturer'sdrawings
the test dates,
humid,
etc) and any
indicate
also
Signal status
positions.
(if applicable)
off, tripped, etc, must be demonstratedas working
Overcurrent
trip settings should be
correctly.
comparedwith the motor FlC rating. Motor starter
backupfuse size and type may be checked against
V consumers.)
should
will test the normal operation of
its local, remote and emergency
showingthe motor/starter
that an owner-approved
The surveyor will require
which shows the
megger test form be completed,
tests on all main 440 V
results of recent insulation
The form
from
starter
control
220
connections,
carbonised
contacts,
pigtails on moving
badly
on coils,
arc chutes and signs of overheating
transformers
and resistors. Dust and weatherproof
sealing featureson a starter must be in place and
in a serviceable condition.)
Functional
and
This
examined.
loose
worn
anchors
Resistance)
Insulation
be
also
will
would include an inspectionfor
to
danger
consequent
The earth strap electrically
the frame to the ship's hull
(zero
volts)
eliminate the shock hazard to personnel.)
against
plate.)
rating
and misaligned contacts.The generalcondition
wire
become
operators.
7.8
checked
be
With starters and associated control
such
gear,
as remote stop/start buttons, regulating
resistors
will
check
for badly burned
etc, an inspection
ANSWER)
Without
will reveal
test on a motor
any vibration
problems, undue noise and worn out bearings.
On load, the motor
current
running
(shown on the
A running
the value indicated on the motor
QUESTION)
137)
Requirements
Survey
Emergencylighting,
fire
SalAS
must be functioning
pump
and
other
emergency electrical equipmentlisted
Electrical
regulations
interlocking
arrangements
under
correctly.
between
must be
switchboards
the main and emergency
whether)))
initiation
checked. Auto-start
relays,
Practical Marine
138
Electrical
voltage or frequency
and tested.)
Knowledge)
operated, will
notices and
examined
be
personnel
and goggles)should
batteries. The ventilation
The ship's emergencybattery
and its
installation,
In particular,
charging rectifier, will be examined.
the battery environment
must
be dry and well
ventilated. The battery
must
be clean with
tops
terminal
and connections
posts
appearing free
from
corrosion.
7.6 illustrates examples of
Figure
conditions
caused
unacceptablebattery
by the
failure to carry out regular maintenance.Image
shows
the contaminated
terminal connections
(a)
of NiCd batteries
used
as emergency
backup for
various ship's services,and image (b) shows the
burst casing of a lead-acid,maintenance-free
set
used
for automatic backup power
battery
battery locker will
clothes
(gloves, apron
safety
to the
available
adjacent
for the
arrangements
checked.)
be
equipment should be checkedfor
and correct
loose connections
and alarms.)
of indicators,
instruments
charging
Battery
dirt,
be
overheating,
functioning
The surveyor may
maintenance
battery
replacements
7.11
Parts
also
require
be
completed
to
list
filled
of
a battery
with the
dates of
in.)
Gear)
Steering
supply.)
.. -)
how
an electrohydraulic
Figure7.7 shows
the
can
be
from
gear system
envisaged,
..
\037)
viewpoint,
. ,)
'o! .- .)
as being in three
.
Power unit
.
steering
control
.
indications
and
The
power
unit
comprises
either
motors
electric
duplicate
side
of the
main
switchboard. On many ships one of the steering
gear motorswill be supplied via the emergency
the
SOLAS
switchboard, as recommended
by
for vessel types such as passenger
requirements
.)
(a))
ships
ferries.)
and
.)
{\037)
\\..)
......, .)
!Y)
---)
;
-:-:- --
The
motors,
starters
switch
units
will be
criteria
outlined
.
and any changeover supply
inspected under the same
in the section on motors and
earlier
GO
.....
.,.
-.... ,)
starters.)
I)
.
\"
'1._')
.\037\037:.:..
-
,--.\"
\\\037\\it:\037\037
\037-. ---
-.-...........-...)
-\037.
\037..,----
-)
-\037
j)
. r \037
, \037\037-:..
\037
!'AI1\"::C;\037
S
__\"
s,
\037
the bridge consoles, as well as
from the steering gear room,
should
be available.
Main and alternative electric
facilities for the
supplies, including
changeover
any
the steering
wheel and for the
electric control
from
7.,)
'..\037\037\037\"\037\037
;:\037)
C'J)
.11)
(b))
conditions)
swung
greasing of all
protect
tested.)
gear and its control
must
be
tested
when driven by a single steeringgearunit
connections
batteries
be
for its response. This is
to be that the rudder must be
specified
in 28 seconds
from
32\302\260
to 32\302\260
starboard
port
functionally
generally
will
must
The steering
7.6 - Unacceptable battery
and
Regular
cleaning
with acid-proof
grease
steering
auto pilot,
..)
from
control
Rudder
emergency
'\\f\037
\\.'-'\037.......,,\037
.'
.....
.\037,..
\037
, .':\\;
.-.
\037
.\037\037)
Figure
parts:)
alarms.)
and starters suppliedfrom
,
steering
surveyor's
should
from
sea humidity.
being contaminated by aggressive
level
Battery electrolyte should be at its proper
and have the correct value
of specific
gravity (SG),
which
should
be checked
with a hydrometer. Safety)
take half that
time
when
and
it
on both
operating
can only
response
loaded
and under
steering gears. A fully loaded
be obtained when the ship is
indications
must
way at sea. Steering gear status
be operating correctly in the steering
flat, main
control room and on the bridge.The rudder
position)))
Periodic
;.-- -)
.\037)
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.'. \\...
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.
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,
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i .. \037'';
,'{.' ..'\037
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tap.,I.
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139)
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, ..- i,)
Requirements
Survey
il
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(to'..
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Steering
r----------------I
I
I
I
I
control)
+
Power
unit)
Indications
-----------
0
0
1
and
I
alarms)
Rudder)
Figure
Main
7.7
steering-gear
components)
indicators on the bridgemay be checked
during the
The
of
the
bridge
steering gear.
testing
indication
should be compared with the direct
indicator on the rudder stockin the
mechanical
7.12
functional
flat.)
steering
Motor
alarms can be initiated
the action of the overcurrent
by
failure alarm should be alsotestedby
the
action of the voltage monitoring
simulating
fluid low level alarms must be
relay.
Hydraulic
checkedfor correct initiation by the oil level switch.)
that
Remember
have
overcurrent
circuit
protection
are
essential
a steering
gear motor does not
trip protection; the only.main
is from 'the backup fuses, which
for short-circuit
surveyor
navigation
relay.
protection.)
Light
Indicators)
The
overcurrent
simulating
The phase
Navigation
will expect
to prove that the
light monitoring system operates
correctly and gives the appropriate
broken wire or burnt
This
lamp.
an
removing
appropriate
alarms
can
for a
be achieved
by
fuse.)
The power supplyfor the navigation
lights must
be duplicated (usually the alternative
is
supply
obtained
from the emergency switchboard)and
the
facilities must be checked (see
changeover
Figure7.8).)
the
Although
part
survey
the
of
actual
the
safety
will
include
lights.)))
are
the
electrical
equipment survey,
a check on the supplycablesto
light fittings for navigation
Practical Marine Electrical Knowledge)
140
and
Alarm
indication
\037
.
supplies
/
Main
Buzzer
o
Main
light
Indicator
Q9
.
.
Alarm
relay
Fuses
Power
Change
supplies
(4 off)
over
Auxiliary
To other
switch
light
navigation
Navigation
circuits
light
,I\\\"
.....
MAIN
MAIN
STAND BY
TOP
FORE
.,
-
SIDE
PS
- '
0
0
... ..
-
\"...-
.
UMS
7.13
If
your
ship
0
D
RESET
by
STERN
CUSTOMS
LIGHT
SPARE
STERII
SUEZ5TERH
RED
0
ON
DIMMER
panel)
automation
Class
for
calibrate the process transducers,transmitters
alarm
the
action
will
be
to the
paid
generator sets' relatedsafety,
alarms
Initiation
and
annunciators.)
Attention
associated
with the propulsion, auxiliary
and associated
systems (eg lubrication
or (more accurately)
by
simulating
under the expected fault condition.)
that the overall sensor (pressurestat,
flow
level switch, etc) is
switch,
thermostat,
is more involved. Specialist
functioning
properly
contractors may be required to service and
To prove
and cooling)areto betested
for correct
operation.
Testing of the safety devices from the various
is relatively straightforward. This can be
systems
achieved
the relative sensor by
by either
operating
hand
2
..1,.)
. I nBL
of such an installation.)
engines
D
-
machinery space (UMS)operation,the
electricalsurvey will be extended to include all the
controls
and failsafe features
alarms,fire detection,
alarms
II
\037
.
unattended
All
-D
0
Operation)
is classified
00
.
-
1
SIDE
58
-
FEEDINGFROM
1 . MAIN
SWITCH.B.
10021
2 . DBN108
. IIUiL@
indicator
light
0
-D'
.
7.8 - Navigation
0
-D'
. :
\037\037
DAIIGEROUS
CARGO
\037...\037
0
0
-
&I
0
00
,.
.
,
--..
..
....
0
\"...
ANCHOR
FORE
STAND BY
;
.,,
n_.....
Figure
panel)
for lubrication
and
action
propulsion and
particularly
their
and cooling systems.
of automatic shutdown,
slowdown or reduction features will be tested.
Essential
drives for lubrication, cooling and fuel
are duplicated
and arranged so that
supply
one
can be selected on a duty/standby
pump
basis.
Loss
automatically
at the duty pump
start up the standby unit.)))
of pressure
should
Periodic
141)
Requirements
Survey
main
UMS requirements demand that a standby
starts
and
closes
onto
generator automatically
dead
of the
loss
on
busbars
as possible.
quickly
It
generator is started
is
that the
a few
seconds
after
as
generator
duty
usual
standby
in
FIRE
A.LA.R)
the
of blackout.)
event
BREAK
and supplyvoltage
and
line (MSB-ESB)
transfer
the
disconnecting
circuit breaker from either
generator should then run
the
to
proven
battery backup.
power supplies
must be
system
the
of
and its trickle
battery
and will be tested
from
correctly
the bridge and wingsconsoles,engine
control
room
and at the emergency position alongsidethe
The
for
alarm
UMS
the
system
to verify:)
the
the
of the
duty engineer
accommodation
engineer
duty
call system is operating
ie in the cabin
areas,
mess
and
and in the duty
lounges
the
is allowed 2-3 minutes to
engineer
duty
respond to a machinery
alarm.
the control
not reached
the alarm within
this
a dead
time,
smoke,
visual
engineer
and
accepted
man alarm
in the
must
and test of the fire
be performed.)
heat
and flame
inspection
complete
apparatus
correctly
the
to initiate
alarms
sensors must function
the appropriate
on the
bridge,
detection
in
the
audible and
main
control
during a full
demonstrated
an engine
engine
test
survey. Electrical equipment
with engine control
as usual for wear and tear,
loose connections
and
cleanliness,
associated
and
connections
will
be
examined
insulation
level,
overheating.)
type must also be examinedand
working
order.)
tested
7.14
Tankers)
in the hazardous
areas of oil/
other ships carrying potentially
dangerous cargo, will be surveyed
during the
Electrical
gas
equipment
carriers,
and
periodic machinery surveys and
surveys.)
during
docking
and
annual
to be
The mostcommonform of hazardous
area
electrical equipment is the flameproof
enclosure
Exd on the equipmentcertification
type (marked
This type of enclosure will be found
on light
label).
and
alarm
fittings, motors, starters, push buttons
bells within the hazardous zones. (See Chapter 6.))
The
room and in the accommodation.
Hand-operated
fire alarm switches (call points)of the 'break glass'
proper
of the electrical equipment
and indication will be
alleyway
to the engineers' accommodation.)
adjacent
All
If
room
should be sounded,generally
A
control
engine
alarm panel
bridge
has
features
operational
main
best
That alarms displayed on the main
console
to the
in the engine control room are relayed
that
controls and emergencystop buttons
function
must
engine.)
arrangement
usually includes
It will
be necessary
to inspect
Tests are madeon
.
must be
satisfaction.)
switchboard.)
during
in
together with
(if applicable),
power
the general condition
charger.)
that
level alarms,
bilge pumping
to the surveyor's
Main engine
electric
standby
The standby
.
..-.\037\037\037)
glass switch)
bilge
duplicate
automatic
nominal speed
up to the
emergency
7.9 - Break
Figure
The
The emergency
side.
to the overall
alarm
monitoring
inspected and tested.)
.
-:!--
of the
load
the
emergency consumers by the emergency
of
must be demonstrated. The initiation
generator
can
be
the automatic
usually
accomplished
startup
The main
GLAss
Qt\037OR.N
lJRfTV)
startup and taking
Automatic
by
p\037\037ss
tested.)
be
wi II
.........
.
This is followed
sequential
re-starting
by automatic
fuel
of essential auxiliariesfor lubrication,
cooling,
of the system
and steering. The correctfunctioning
in
flameproof
enclosure
will
be
inspected
for
cleanliness (which
affects
the surface
corrosion
and secure mountings.
On
temperature),
the lamp
bonds
lighting
fittings, the cement that
glass to its frame must be closelyinspectedfor)))
surface
Marine Electrical
Practical
142
Knowledge)
--)
end
Spigot
........)
.,*)
Adhesive)
\037
'O'-rlng)
--
ring
Sealing
r-/)
.)
,/)
Socket)
'.)
Flange joint)
7.10
Figure
- Exd
Spigot
edges
be
painted
to be switched on. Similarly,
flameproof equipment on deck must
correct
the
with
be
(approved)
Exd
(Figure
fitting
checkthe condition
corrosion, pitting
of
or
7.10)
may be
its flamepath
scratch
communication
must be
areas
Exi
on
the
Certification
safe
intrinsically
(marked
label).In most cases, zener barriers, as shown in
in line
with intrinsically
7.11, are connected
Figure
in a safe area just
safe circuits and are fitted
gaskets
opened up to
surfaces
outside the hazardousarea.)
for
marks.)
The Ex Certification label and equipmentrating
label
must
not be painted over.)
Remember that no
are allowed without
Certification
permission
surveyor
situ
as
in
and
to Exd equipment
from the
alterations
The
it is
is
generally
equipment
conditions
arise.
that
a fuse
test zener barriers
easily
involve special equipment
accepted
function
This
circuit fault
is no different to accepting
will blow when a short-circuit
occurs.)
the surveyor
will
Here
to the ship'shull.)
is allowed)
R)
Hazardous
r)
F)
1)
area
terminals)
4)
- Exi barrier circuit)
visually
inspect
the
barrier installation. The barriers must have
secure
connections
and be properly boltedto an
earth strap which, in turn, must be solidly bonded
3)
7.11
protection
when
correctly
zener
rooms have pressurised light fittings
Exp on the Certification label).
to confirm that
the
are
necessary
fittings
pump
purged and pressurised beforethe light
Figure
such
that
Authority.)
(marked
it
cannot
this would
will
However,
Some
should
lights
air pressure
the
equipment used in hazardous
or '0' rings in place.)
An
if
and
instrumentation
Electrical
as
judged
the
automatically be switched off
drops below its set value.)
of flamepath flanged joints must not
over or impeded in any way. Exposed
weatherproof
joint)
flamepaths)
cracks or indentations.All bolts must be in place,
and of the correcttype.)
evenly
torqued-up
The
Screwed
joint)
Safe
Z2)
Z1)
area
terminals)
2)))
Chapter
Eight
Electric
Propulsion
Electric
8.1
and
Electricpropulsion
of
has
ships
times
other
a long but
ignored as a drive
virtually
with
and are, built
is
propulsion
of vessels
have
been,
that
has
sets that
generating
to provide power to both
the
can
be
of
Flexibility
.
economical part-load running
.
ease
.
low
of control
noise
advantage
the
prime
characteristics.)
of layout
Flexibility
An
vibration
and
electric transmission is that
and their generators, are not
of an
movers,
to have
constrained
any particular relationship with)
and)
..1)
\".....:.._.
I.')
\",
r-
Figure
8.1
-
..
.
,- \037
.............
. .
..._-.
..------------..----:==--..----.....----...-.--......
::::-=========:::===-
--
\"\"
\"\\
- Modern
\037___. _
.:.===-
.
-
.
-
. .
..'
.. .. \302\267
..
.. . -.. . ;-i . .:- ..-:\037=
\037-.-\037:;
: : : : : : : : \302\267
\302\267
\302\267
....
t . . . . . . . . . . . . . . . . . . . ......
.. .
.
\037
\" .
-. :
\",,:\" '.\"
_...._ - \037 '\",'
-
cruise ship)
-
..
::==:t\037
- - - -.-.....
- ------ --.--\037---.
....-..._-\037-n.!
.
....:!!8.....\037_.;.:
___\037\037.\037.\037-
'\037;F:;F--:;a-..
..\".\\.\037_\"
'-
.
I' j J.L\\I'. t i
...
-\037
..-..;
.\037- -;;..,
.:.:.::.::...==::::-.-..---.--::.-.:::
and
propulsion
...)
..:.-)
\037;
.\037
it
layout
load diversity between ship serviceload
.
used
system
propulsion
possible
.
propulsion.)
to the propulsion motors,directly
to the
coupled
acted
propeller shafts. The generator/motorsystem
as a speed reducing transmission system. Electric
for auxiliary
ship services required the use of
power
constant
separate
frequency
generator sets.)
system
shaft.)
per
for some
installations,
to justify the complication of electric
and these include:)
propulsion
the
Early large passenger vessels employed
which involved the use of
turboelectric
system,
variable
and therefore variable frequency,
speed,
turbo-generatorsets for the supply of electric power
A
would
There are reasons why,
electric
electric
with
motors
multiple
system.)
but a wide variety
systems,
this
and
the
required propulsionpowerwas beyond
capacity
DC motor,
there
was the complication
of
have always been the largest
ships
Passenger
commercial
vessels
voltage
of a single
been
has
it
but
frequency
system to
satisfy the requirementsof the ship service loads.
The provision of high power variable speed drives
a fixed
from
and frequency supply has
voltage
In addition,
when the
presented
always
problems.
history. There have
been periodswhen
it has
enjoyed
popularity,
with
number
a significant
of installations being
at
clear advantages,
to be a fixed
have
chequered
undertaken,while
has
services
ship
Propulsion
Scheme)
somewhat
Voltage)
High
:.=.:\037.:=
== h='
r.:\037i;r:\037:\037
__;\037\037\037: .
_. '_ _
-_ .
. ..... ..
................
..
. .. .
\"
....
.....)
\302\267
--)))
. . .
J
_
... - - .. .
.. .......:\037....
- ...\037. -...) -. .,
\037-:,\",..'
\037
\037
---
:.\"
\037
----;;- -
\"\".
..
I
144
Practical
Marine Electrical Knowledge)
load as a cable run
is a versatile
transmission
medium. In a ship propulsion system, it is possible
to mount the diesel engines, gas turbines,
in
etc
locations
best suited for them and their
associated
so they can be remote from
the
services,
propeller
shaft. An example of an electricpropulsion
plant
It is
the
layout
is shown
Load
diversity
in
with
very
three partially
electrical
a substantial
relatively constant, does involve
of generator
Economical
load which, although
will result
loaded
load
in
the
three
sets
which is not an
It is not necessary
to
factor,
ideal operatingcondition.
the
to provide
operate generating sets at part-load
spare capacity to be ableto caterfor the sudden
loss of a set, because propulsion
load
reduction
be
available
may
instantaneously and, for most
a
short
time
reduction in propulsion
vessels,
power
does not constitute a hazard.)
size
a significant
will
monitor
propulsion
regulator
continuously
the present generator capability and any generator
will immediately result in controlled
overload
limitation to the propulsion motors.During
power
The
plant.)
running
part-load
This is best achievedwhen
is a central
there
generation systemfeeding propulsion
and
power
example.)
3 x 440 LV
console
-\",
Diesel
-- \037
\\\\
failure
are
requirements
of one generator
a hazardous
generator
situation.)
sets)
;, \037)
\037)
\037
;\\\\
-\\\\..- ,
and
Main Switchboard)
e \037
1:1EIa: I'J
\037
\037
\037t:\037
1i1'J\037
\037rJ2
\037\"a
. .... ;\037\037\037
\037 .\"
II I. I
PO\" ._ '''1.., !'l'!U\"'.wAl: .r.o:...wn
._ un\" \".....JiI!\302\243Ii \037 II.T,....
Pro p ulsion
power
propulsion
manoeuvring,
below system capacity
is not likely to present
ship
vessels being a good
with passenger
services,
the
at a 670/0
operating
Certain types of vessels
have
a requirement
for
substantial amounts of electric
for ship
power
services when the demands of the propulsion
are low. Tankers are one instanceof this
system
situation
and any vessel with
a substantial
cargo
load
also
discharging
qualifies.Passengervessels
have
and
load demand. In a four engine
for
installation,
example, increasing the number of
in
from two that are fully loaded to
sets
operation
to
capacity
8.2.)
Figure
a typical installation would have
diesel generator sets and,
eight
of all the sets, it becomes
parallel
operation
easy to match the available generating
likely that
between four
,
Engine
Control
....
\037.)
.
Room)
,L \\
t \"r .)
,
\\ ')
\" ,)
'
,)
l')
r=
.)
(y\037\0371
\037es
f:I..C II
Converters)
1
\037
I II 1:1
\037
r
-)
\037f:lS
f.I C
IJCIS-C
\037
.
I)
-f
:-:-)
..,-\037,)
3 x 6.6kV HV Main
Switchboard)
.-4
..-:--)
..,-.')
'f)
,
\\ .')
\037\037)
I
I)
,)r
.........
...
'<)
.\".\037
I)
\",)
Y
Propulsion
electric motors
PEM)
\"\"\\)
Engine
Figure
8.2 - Propulsion
plant
layout)
Room)))
Electric
synchronous motors with fixed pitch propellers
control
speed
(FPP) driven at variable
by frequency
from electronic converters.A few installations
have
the combination of CPPs and a variable
speed
motor. Low/medium power propulsion(1-5MW)
be delivered
may
by AC induction motors with
Ease of control
The
of controllable
use
widespread
(CPP) has meant that
were so readily
the
pitch propellers
facilities that
electric drives are
control
with
available
the
same
no longerableto command
premium.
Electric drives are capable of the most exacting
demands
which, in
general,
anything
that
with
regard
variable
to dynamic
performance
exceed
by a wide margin
is required
of a ship propulsion
noise
diesel
in warships,
importance
and this is of
oceanographic
vessels and cruise ships.With
survey
and
warships
engines
a fixed output
frequency.
of practical
overview
in
shown
Figure
the
a pair
of high
efficiency,
use
favoured
most
All
to give
driven prime
are likely to become
Gas
generators
turbine
external
drives,
large
notably from ice
propulsion
motors
are
pods mounted outside of the
ship's hull. These are generally referred to as
in Figure
8.4, as the whole
azipods, as shown
0
pod unit can be rotated through 360 to apply the
fitted
within
rotating
in any
ie in azimuth.
horizontal
direction,
and
means
that a conventional steering plate
side thrusters are not required.)
thrust
option is
AC)
voltage
high
smaller
breakers, somevery
electric drive options is
power,
to
from
8.3.)
For very high
driving
the propeller drive shaft
is directly
Conventionally,
driven from the propulsion electricmotor
(PEM)
from inside the ship. From experience obtained
survey
critical
vessels, it is noise into the water that is the
it is structure-borne
factor, while with cruise
ships,
noise and vibration
to the pass\"enger
spaces that
to be minimised.)
has
An
motors
constant-
AC
movers for the generators
more common in the future.)
with
a drive
DC
voltage converters.)
The prime moversare conventionally
speed
An electric motor is ableto provide
very low vibration characteristics
or by
converters
frequency
with variable
system.)
Low
145)
and High Voltage
Propulsion
This
stern
fixed speed prime-movers
at 60 Hz)
AC generators
driving
'---..
........
\037
........
'-'\"'
'-
,,--...
.\037
\"
\"\"'\\
--\037
_.
'--\"
'-
..-.....
\\.....-.....
'\"'
.-...
'-....<.
\"---'
--..
I
9)
AC-DC-AC
AC-AC
AC - DC- AC
Synchro
Cyclo
PWM
converter)
converter)
I
Figure
8.3
converter)
Synchronous)
Synchronous
Induction)
FPP
FPP
FPP
- Electric
propulsion options)))
AC - DC- AC
Synchro
0-60Hz)
0-20Hz)
c:::tJ=::>
- DC
L-converter
0-60Hz)
c:::tJ=::>)
AC
converter)
\037)
0-60Hz)
Synchronous)
Cpp
\037
c:::tJ=::>)
Marine Electrical
Practical
146
Knowledge)
Hydraulic
unit)
steering
Slip ring unit
and control)
for power
Ventilation
and cooling)
Installation
block)
o
Hull)
:1
I)
I)
III
-11-)
Variable
speed/direction
motor)
synchronous
Fixed pitch
propeller
(FPP))
Figure 8.4 - Azipod
drive
unit)
is significantly
enhanced
manoeuvrability
and
the
external
unit
by using azipods
propulsion
releases
some internal space for more cargo!
Ship
passengers
while
further
hull vibration.)
reducing
below 1000 V are
'voltages
LV (low voltage). HV (high
is
voltage)
HV system
marine
any voltage above LV. Typical
voltages are 3.3 kV or 6.6 kV but 11 kV is used
In
marine
practice,
considered
oil/gas
offshore platforms and specialist
ships,
eg on some FPSO
(floating
production,
on some
production
Power
8.2
As
the
demand
ships (particularly
Supply
for electrical
passenger
Network)
power increases on
ferries,
cruise
liners,
the
specialist offshore vessels and platforms),
current rating becomes too high
at 440
V.
supply
To reduce the size of both steady
state and fault
current
it is necessary to increasethe
levels,
system
voltage
at high
power ratings.)
storage
and offloading)
vessels.)
By generating electricalpowerat 6.6 kV
of 440
V, the distribution
above about 6 MW
and
becomes
instead
of power
switching
more
manageable.)))
Electric Propulsion and High
units
diesel generator
requires
fault level to be about 90 kA
circuit breaker
a full-load
each
pf
generator
W
x 440
J3
<p
system at 6.6 kV
x 0.8)
requires
the
P
J3 x V x Cas
A
3280
The componentparts
standard
now
of
An
main
switchboard.
Large
A
Figure
HV
HV
and
transformers
high voltage
power system is
8.5. The
generators
HV
all
of the
form
a
ship's electrical
o
o
o
be
o
o
DE1)
Experience
would
are the two synchronous
The principal
consumers
AC propulsion electricmotors (PEMs),which
may
12 MW or more in the full away
each
demand
condition. Each PEM has two stator
windings
HV switchboard
separately from the main
supplied
and frequency converters.In an)
via transformers
switchboard.)
o
ship.
AC voltages.)
three-phase
power
the
the
services. On a largepassengership with electric
each generator may be rated at
propulsion,
about 10 MW or more and produce 6.6 kV, 60 Hz
motors
from
in
central power station for
HV supply system are
with HV diesel generator
consumers, such as thrusters, propulsion
are fed directly
and HV transformers,
HV cables,
of a
example
shown
an
equipment,
sets feedingan HV
MW system
HV motors.)
HV
2,000,000 W
== 219
J3 x 6600 Vx 0.8)
<p
at 6.6 kV
a 9
electrical
for a
switchboard and cables to be rated
circuit
fault level of about 9 kA with generator
breakers rated only for an FLC of 220 A.
1==
of
shows that
HV switchboard,
==
V
of maintenanceoverthe life
about 20% more expensive for installation
costs.
The principal parts of a ship's
system
at HV would be the main
operated
generators,
(FLC) of:
2,000,000
J3 x V x Cas
The same
0.8
must be simpleto
and require
a minimum
priced
reasonably
and system cablinghasto handle
current
P
I ==
operate,
switchboard
the
and
load
HV system
economical
An
For example, a three-phase 6 MW ship's
on a 440 V system
supplied
by 3 x 2 MW,
147)
Voltage
o
DE2
o
o
DE3
DE4)
o
o
o)
.!.
T)
G3
G2
3-)
3-)
Q)
3 x 6.6 kV
60 Hz
HV MSB)
Harmonic
filter)
Harmonic
filter)
M)
Figure
8.5 - HV power system)))
M
M
M
M)
M)
Marine Electrical
Practical
148
a PEM
emergency,
a
A few
from
may, therefore,
a reduced
with
motor
half
Knowledge)
be operated as
power output.)
large induction motors are suppliedat
HV main switchboard with the vacuum
6.6
kV
the
and
I
As
the
A
.
Other main
feeders
the 440
supply
V
low
transformers.An interconnector
cable
ER sub to the emergencyswitchboard.
440
around
Some
directly
The
voltage
links the
Other
(accommodation, galley, etc)
the
ship are supplied from the LV MSB.
installations
may feed the ship's sub-stations
with
HV and step-down
to 440 V locally.)
PEM drives
in
this
are synchronous
example
low voltage
a controlled
require
Motors
AC
Induction Type
The mostcommonmotor
AC induction motor with
induces currents
the rotor.The interaction
that
I
between
the FLC
for a
motor
standard
ANSWER
on
rotor
on the shaft from
IR. To
its running speed must be slightly
that of the stator rotating
field.
This
ranges
about 1-5% over the load range for
induction
motor.)
between
The speed ns of the
rotating
is fixed
number
stator
cage
winding
stator
flux <I> and
is called the slip speed and
difference
kV.
of
rotor,
than
lower
the
into
where cp is the phase angle
be able to induce currents
coscp,
R
<I> and
the
into
(a) 440 V
the
by
a
flux produced by the
of winding pole-pairs
'p' and the supplyfrequency
'f' as:
ns
==
f/p
(rev/s).)
145.8A,729A
(b) 9.7A, 49 A (assuming
'DOL
== 5
x
For example:
'FLC))
For a motor
designed
50 Hz supplywith
of
8.3
Review
Electric
motors
DCor AC.
of
Motor
Operation)
ns
for ship propulsion
may be either
AC versions
be
induction
or
may
The
the
rotating
== 50/2
but
== 25
actual
the
n R == 960/0
of 25
for 4-poles
a full-load
slip
(p == 2) to run on a
of 4%, the speed
flux is:
rev/s
(1500
rotor speed
== 24
rev/s
rev/min),)
will
be:
or 1440
rev/min.)
models.)
synchronous
type induction motor is simpleand
some practical disadvantages.
When
with a fixed voltage and frequency,
supplied
the
motor
runs at an almost constant speed and
has
a high starting current of up to seven
times
its
the
While
DC Motors
DC motor
Figure 8.7).)
(see
a torque
produces
X
R
T == <I> X I
%
a cage
Three time-displacedsupply
currents
to the three
stator windings produce a rotating
field
magnetic
QUESTION)
calculate
Assuming 100 efficiency,
then estimate the DOLstarting
current
100 kW, 0.9 pf induction
three-phase,
supplied at:
rotor
to
is a three-phase
drive
rotor, because
as there are no electrical
robust
is extremely
current
(a)
to
is able
voltage.)
connections the
switchboard.)
6.6
be
can
drives.)
750 V DC
it
excitation supplycurrent
to magnetise
the rotor
from
the HV
poles. This supplyis obtained
switchboard via a step-downtransformer,
but
an alternative
would be to obtain
arrangement
the excitation
from the 440 V ER main
supply
(b)
the DC motor
is that
the
major drawback of a DC motor
of
the
armature
current
is
necessary switching
achieved
a
mechanical
'commutator'
on
the
by
shaft.
from the maintenance required
Apart
rotating
for
the
commutator
and its carbon brushes, the
is limited to about
appliedvoltagefor the armature
V sub-stations
motors that
and field flux
The
(LV MSB) via step-down
switchboard
current
thruster
air conditioning compressors.)
three
main
and one aft
thrusters
forward
Figure 8.6).)
controlled,
armature
field flux
magnetic
for
provide very useful torque/speed characteristics
power
\302\267Two
the
<I> is
current (see
armature
is the
independently
are:)
These
breakers.
due to n == V/<I>, where
where very high
control
is acquired.
torque
precise
speed
Traction
such
as
electric
drives,
trains, submarines
and offshore
use
DC
motors. The
drilling
rigs,
drives
are
still used
and/or
torque is governed by T == <I> X IA and
the
speed
is)
cage
low
cost,
it has
full
load
value.)))
Electric
Propulsion and High
149)
Voltage
Stator core with
field poles
projecting
./)
* r-_
-,/\"
/
.)
I
/
a)
I
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r.
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CI)
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cu
commutator
with
<P
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u:)
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Rotating armature
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r \037
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:
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1
I
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\",
I /=9
/
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I
//
o)
motor
circuits)
conductors,
and brushes)
8.6 - DC motor circuit)
Figure
3 -
Stator core and
input
current
phase
N
windings
//
I I
L1
Force (F)
.
0
.4
..
\\
L2
....
.-
L3
\\
Force
0
(F)
l 1
, I
,
Rotating
flux
Rotating
stator
stator
flux
S
Twisting force on rotor bars
= F x
(torque
radius))
- Induction
Figure
8.7
If the
motor
440 V with
in
load
example
load rated output
efficiency of 90%
its full
is designed for
100 kW, an
and
a power factor of 0.8 lagging,
current will be found from the
above
the
a full
motor action)
supply
of
that
is a three-phase motor
produces
of
at a speed
a magnetic field rotating
==
the
induction
like
motor type.)
f/p
just
(rev/s),
ns
power formula:)
three-phase
The
p == -V3 x
the
V L x I L X COSt/)'r
electric
power
input
rotor
excitation
is
100/90
%
==
111.1
kW
Type
Synchronous
This
has a set of magnetic
that locks in synchronism
rotati
n g fl ux.)
This
means
poles
with
with
DC
the stator
and
IL == (111.1
then
x 10 3
)/-V3.440 x 0.8 == 182.2
the initial
about 911 A.)
starting
current
surge
A
is
that the shaft is always
speed
synchronous
(see Figure 8.8).)))
set by
the
supply
running
at the
frequency
Marine Electrical
Practical
150
Knowledge)
core and
Stator
.-_-----.... N ,__
\037\",
\",\"'\"
.....-............,
\"
; ---'....
-,J'- \037\037
,I:'
\037.I
,,/ \"'./'\"
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.-
phase windings)
3 -
Input
current)
\037
L1)
/
II Ij
I':cn'
--I
I
.)
L3)
,Z
,
\037)
!
:j
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Force
-
(F))
Force
\\ \\\\
\\ I
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,
I I
I II
I
I
,
I
,r JI
I
J
I /)
I
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.'.....,........
,'----\"
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,..\"\" /,/,
- ... ...-....\"'\"
, I
....
............-----...' '--------,'-)
-
Rotating
stator
{f)
i
I
I
,
I .
, I
:
, ,.:
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1)
.
to \\
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L2)
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I
I
I
I
I
-I
I)
(F))
..)
\\
Rotating
stator flux)
S
flux)
Twisting force on rotor poles
with sync. with stator flux
(torque = F x radius))
locked
8.8 - Synchronous
Figure
To
motor action)
the motor from standstill can
- it is either:)
start
problem
be a
currents.
This can only be overcome
of the stator supply
frequency
prevent
overheating
(by over-fluxing)
of the motor
while
frequency.
the
changing
supply
by
To
rotor
.
at a very low frequency with
forward
\302\267 Pulsed
poles
up
dragged
with
motor
normal
Basic
Many
by energising
synchronism
Advanced
the
the operating power factor
of
motor can be lagging or leadingas
by the size of the DC excitation
running,
a synchronous
this
is determined
field
as an induction
cage rotor,
to slip speed
an embedded
cu rrent.)
control
speed
installations
industrial
of motors
can
direct and smooth speed control
benefit from
of a drive that is
the
material
moving
process
(water, compressed
controlled
air, oil, conveyor belts, lifts, etc). Smooth,
acceleration and deceleration also reduces
shockloading
in the system.
For a DC motor
on
a fixed voltage supply, this is achieved by using
resistance
in the armature or field
circuits
to
control the armature current or field
flux
(or both).
The disadvantage is the overall
loss
of efficiency
due to the power losses in the external
control
resistance( s).)
For an AC induction
on a fixed voltage
control would
only
current,
but
the
motor
and frequency
supply, resistance
affect
the size of operating
is constant due to the fixed)
speed
motor
or synchronous
changing,
frequency
voltage must be changedin direct
excited, or
then locked into
DC rotor field.)
For
the
speed
the supply
proportion.)
control
drives
Computer-controlled
speed
(VSDs)
are applied to DCand AC motor types of all sizes.
The most popular
is for induction
application
motors for the main industrial
power
range, but
in
motors
are
used
installations.)
synchronous
large
variable
The AC motor drives produce a variable
output
by fast
Drives
may
frequency
or
voltage switching from a transistor
which
be
AC/DC/AC
thyristor converter,
may
(PWM
and synchroconverter)
or AC/AC (cycloconverter).
These drives use a mathematical
model of the
motor
and
the computer
controls the converter
to precisely
match the set inputs
for speed,
output
etc.)
acceleration,
deceleration, power limits,
torque,
be tuned to create optimum
against
the
connected
Problems
shaft
load.)
arising
The fast switching
(or chopping)
to VSDswill produce
a distorted
includes
high
frequency
of the voltages
waveform that
harmonic
whose frequenciesare exactmultiples
fundamental
conditions
braking and energy savings
for run-up/down,
(base frequency)
components
value.)))
of
the
Electric
for an AC drive. The set
be converted by controlled
rectification
(AC/DC) and/or controlled inversion
motor type.)
(DC/AC)to match the propulsion
of a 60 Hz
For example,a 7th harmonic
fundamental will be at 420 Hz. Such harmonics
create additional
heating
possible interference (often
interference or RFI).)
in equipment
called
radio
solutions
frequency
include good initial
problem
design,
filtering
system
AC
busbar
and
to a harmonic
+ voltage
frequency
A
Practical
151)
and High Voltage
Propulsion
and
rectifier
basic
can
that
must
voltage
only
uses
conduct
semiconductor
current in the
(A) to cathode (K),
anode
this
and
diodes
of
direction
is automatic
positive than K. The diode turns
when its current falls to zero.
in a single-phase
AC circuit, a single
conduct
only on every other half-cycle,
when A is more
suppression)
off
automatically
Therefore,
8.4
Controlled
diode will
called half-wave
Rectification
and Inversion)
The
AC electrical
three-phase
generated
power
bridge formation will
and frequency.
supply on a ship has a fixed voltage
This is generally at 440 V and 60 Hz, but for high
power
demands
Speed
control
it is likely
to
kV and
be'6.6
voltage
two
only
having
DC
the
An
also
output
produce
full
a full
wave
wave
terminals,
cannot
from the rectifier.)
.
\"
--. --
- ..- ---:-,.- '...--.'
-,.\037
-....
-'---_:-:-<\037
-. -
. ,\037
\037
\037\037
.. ._, . .\" ....:,:--\037
.
., '._
h
-.......
-.,.- ..
.....\".- ,\"
-' \",
\" - \037
G)
......)
K)
Gate
VAG)
control
circuits)
IDC)
Set input
value
1)
+)
PUCK
I DC)
------------- -.....
/
J
-_
thyristor)
//
II
,-
//
II
--!\037---l---- ---\"\"-----f\037------
!
Delay
angle:
Half-wave rectified DC control
controlled
Figure 8.9 - Single-phase
rectification)))
,---- ,
A ver8ge
1-\037
current level)
L \037 J)
by
direct
switching)
DC
bridge
A diode,
control the size
operation.
A)
\037
.
- >--\037
,- , .
A
single-phase
three-phase
equivalent
six diodes for
requires
60 Hz.)
for a propulsion motor requires
for a DC drive and variable)
,
\\
output.
voltage
of
variable
Other
rectification.
with
two
circuits, using a bi-phase arrangement
diodes
and a centre tapped transformer,
will create
full wave rectification. Similarly,
in a
four
diodes
Load)
Marine Electrical Knowledge)
Practical
152
Process
Rectification
Controlled
For controlled rectification,
a set of three terminal
(for high
to use
necessary
such as thyristors
(for low-medium
it is
devices
or transistors
currents)
currents ).)
control circuit using a thyristor
A basic
AC/DC
switch
is shown
in
diode, a thyristor
with a
Figure
8.9.
Compared
an
extra
(control) terminal
has
called the gate (G).The
will only
thyristor
when the anode is positive
cathode and a brief trigger
with
respect
voltage
conduct
is applied
pulse timing
decides
the
main
current.
The
switch-on
point for the
load current is, therefore,
(by diode
action) and controlled by
DC
to
rectified
In this circuit,
an inductor coil
delayed switching.
(choke)smoothsthe DC load current even though
the DC voltage
to
use
a capacitor
the rectifier output,
across
which
the DC voltage.)
smooths
wave
Full
chopped
by the thyristor
An alternative to the chokecoilis
is severely
action.
switching
phase AC
supply
six thyristors,
For a 440 V
from a three-
rectification
controlled
is achieved
in
as shown in Figure
a bridge
circuit
three-phase
input
can
positive
to negative
(or
by using a set of thyristor
voltage
switches. A controlled
three-phase
transistor)
8.11.)
thyristor
bridge inverter is shown in Figure
inverter bridge circuit arrangementis exactly
as that for the rectifier. Here, the DC
is
switched onto the three
voltage
sequentially
lines.
The rate of switching determines the
output
For AC motor control, the line
output
frequency.
currents
are directed
into (and out of) the windings
that interacts
a rotating
stator flux wave
to
produce
with the rotor to produce torque.)
Converter
Types)
and
The processes of controlled
rectification
that are designed
inversion are used in converters
The principal
to match the drive
motor.
types of
are:)
motor control
converters
.
8.10.)
same
8.5
with
line voltage, the peak voltage
is 440 x -V2 == 622 V. The equivalent maximum
DC average voltageoutput
is taken
to be about
600 V as it has a six-pulse ripple effect due to the
(rms)
be inverted (switched) repeatedly
to form an alternating
voltage
(AC)
the
between gate and cathode
must be more
(gate
Gate
positive than cathode).
pulses are
voltage
electronic
circuit and the
provided by a separate
(load)
DC
from
The
to the
pulse
A
Process
Inversion
Controlled
AC/DC (controlled rectifier
.
AC/DC/AC
(PWM
.
AC/DC/AC
(synchroconverter
AC
for
for induction
DC
motors)
motors)
for synchronous
motors)
.
AC/AC
for synchronous
(cycloconverter
motors).)
waveform.)
L)
(Current
IDC
smoothing))
L1
L2)
V oc)
c)
L3)
(Voltage
smoothing))))
Figure
8.10
-
Three-phase
controlled rectifier
bridge
circuit)
DC load)
Electric
and High Voltage
Propulsion
153)
+)
u
V)
w)
Figure
AC/DC
8.11 - Three-phase inverter
circuit
and AC synchronous
Converter
This is a three-phase AC
controlled
rectification
for a DC motor
drive.
Two converters
used
different power ratings are generally
of
circuit
motor)
requires
an
Figure
8.12.)
uncontrolled
diode bridge, as shown in
Motor torque is determined from
T == <1> x I and
the speed is controlled from
N == V AI<1>. Sh\037ft
can be achieved by reversing
rotation
either
the
for
current
the separate
control of the armature
(I )
the
and the field current that
produces
magnetic
flux (<1\302\273.
Some
may have a fixed field
systems
the field supply only)
which
means
that
current,
field current or the armature
current
direction.
for
such
a
drive
would
include)
Ship applications
----------------------------1
I
I
I)
+:)
--f7+-)
Field
rectifier)
+)
r-
(
M)
,)
\037)
3 -- supply)
Speed
control)
AC/DC
Nand
thyristor
controller)
DC motor)
Figure
8.12
- Controlled
rectification converter and DCmotor)))
T output)
Marine Electrical
Practical
154
cable-laying,
offshore
ocean survey
and
diving and supply,
drilling,
of the
Converter
smoothing effect
(eg at 20 kHz in
rate
switching
as shown in
Figure
simpler and cheaper, but
be able to
allow
into
From
operation.
braking
rectified DC (link)
motor load to be
supply during a
mains
the
a 440
voltage
AC
V
will be
DC voltage
The
is chopped
variable
into
be closely
the
motor drive
connected
encoder.)
speed
width,
but constant level, voltage pulses in the computercontrolled
inverter section using IGBTs.This
is
called pulse width
modulation
or
process
PWM. By varying the pulse widths and polarity)
a,.-)
1\302\243.
to
tuned
by the
capacitor to approximately 600 V.)
in shape.
to achieve optimum
and protection
limits
control
for the overall drive. Speed regulation
against
load changes
is very good and can be madevery
a shaft
precise
by the addition of feedback from
the
supply,
smoothed
the motor
inductance,
sinusoidal
of shaft
Accurate control
acceleration time
torque,
and resistivebraking
are
some
of the operational
into the
parameters that can be programmed
via a handheld
unit. The VSD can
VSD, usually
so is
will not
controlled
motor
By sequentially directing the currents into the three
windings, a reversible rotating
magnetic
field is produced
with
set by the output
its speed
of the PWM converter.)
frequency
converter),
converter
from the
power
regeneratedback
the
the
output
stator
8.13.)
rectifier stage is not
The input
PWM
a
of
over
0.5-120
currents appearto be nearly
This type of converter
is used for induction motor
drives and uses transistorsas the switching
devices.
Unlike thyristors, a transistor can be
turned
on and
off by a control signal and at a high
to generate an
a wide range
Hz. Due to the
DC voltage, it is possible
averaged sinusoidalAC
of frequencies,typically
submarines.)
PWM
AC/DC/AC
Knowledge)
can be
VSDs, being digitally
controlled,
networked
to
other
computerdevices,
easily
eg
logic
programmable
overall control of
controllers
a complex
for
(PLCs),
process.)
Handheld
Programmer)
.-------------------------------------------------------,
I
I)
....)
.
\"
Variable
Con\037oleffic\037on\037s
L...
])
II)
frequency
AC supply
to motor
three-phase
eg 0.5 Hz - 120Hz)
IGBT
1+
DC
o
I
o
capacitor
I
--8*-
link
-<
e
o)
,
M
3-
\\
4
J
Controlled
1-
Bridge
Fixed
three phase AC supply
- 440 V, 60 Hz)
eg 3
rectifier
inverter
T
d
L-
VSD
- bridge
\037 -:.)
+
IGBT
DC
voltage
input
..
PWM
-<
Controlled
A veraged
voltage
output
A veraged
inverter
,
bridge
PWM principle
8.13 - PWM
converter
hIgh
frequency
..)
(one-phase only
Figure
low frequency
and AC induction motor)))
shown))
Electric
AC/DC/AC Synchroconverter
This
(called a synchrodrive)
to marine electric
drives
motor
and is applied
propulsion.)
A
is used for large AC
of converter
type
synchronous
successfully
very
shown
as
in
rectifier and inverter
8.14,
Figure
has
both
that
stages
for the
turn-off
rely on natural
(line commutation)
at either
thyristors by the three-phase AC voltages
and
end of the converter. Betweenthe rectification
inversion
is a current smoothing reactorcoil
stages
link.)
DC
the
forming
An operational
a
between
exists
similarity
drive.
This view
synchrodrive and a DC motor
considers the rectifier stage as a controlled
DC supply
and the inverter/synchronous motor
combination
as a DC motor. The switching inverter
acts as a staticcommutator.)
The
combination
link
is considered
of controlled rectifier and DC
to be a current source for the
task is then to sequentiallydirect
into the motor windings, as
whose
inverter,
blocksof the
in
shown
current
Figure
8.15.)
The size of the DCcurrent
switching of the rectifier
is set
by the
controlled
Motor
supply)
thyristors.
six-pulse
simplified
converter).)
of synchroconverter
understanding
control is that the current source (controlled
rectification stage) providesthe required
motor
and the inverter stage controlsthe required
torque
To provide
the motor EMF, which
is
speed.
necessary
for natural
of the
commutation
inverter
the synchronous motor
must
have
rotation and magnetic flux in its rotor poles. During
normal
the synchronous
motor is operated
running,
with
a power
factor of about 0.9 leading(by field
excitation
of
control) to assist the line commutation
the inverter thyristors. The DC rotor
field
excitation
is obtained from a separate controlled
thyristor
thyristors,
rectification
circuit.)
As the supply (network) and machinebridgesare
identical
and
are both connected
to a three-phase
their roles can be switchedinto
AC
source,
voltage
reverse.
This is useful to allowthe regenerationof
motor
back into the mains powersupply
that
power
an electric braking torque during
a sudden
provides
stop of the ship.)
DClink
U
L1
V
L2
Synchro-
converter
L3
W
Supply)
AC
synchronous
.
.)
.
Controlled
current
0)
Figure
8.14
-
o
.)
.\037)
\037)
Synchroconverter
circuit)
source)
155)
frequency (and therefore its speed) is set by the
rate of inverter switching. The six inverter
thyristors
six current pulses per cycle (known
as a
provide
A
synchroconverter,
controlled
and High Voltage
Propulsion
Frequencyconuolled)))
motor)
156 Practical
AC/AC
Electrical
Marine
Knowledge)
While
a synchroconverter
output
frequency
to provide an
is able
up to twice that
typically
range
of
input (eg up to 120 Hz), a cycloconverter
is restricted
to a much
lower range. This is limited
than a third
to less
of the supply
frequency
is due
to the way in which
(eg up to 20 Hz), vvhich
this type of converter produces the AC output
mains
the
waveform.
voltage
are
typically
can
easily
in the
Ship propulsion shaft speeds
which
range of 0-145 rev/min,
be achieved
by
low
the
conventional
DC can be controlled
can
voltage
from AC to
converter
three-phase
that
so
the average
output
'
DC 1
in 60 degree
3
shows
8.16
a basic circuit arrangement for
with an approximate
together
for the low frequency
output. The
voltage waveform
shape
(not shown)
corresponding current waveform
will
be more
sinusoidal
due to the smoothing effect
of
and
motor
The output
line inductance.)
has
voltage
ripple content
a significant
frequency
(worse) as the output
It is this
feature that limits the maximum
larger
gets
is raised.
frequency.)
steps
'DC 1
5
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3
5
t'
U
I /
V
V
.: I'
(
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w
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-
)
Stator flux
rotation
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U
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(t\037
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6
2
4
6
2)
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3)
5)
IDC 1)
3)
5)
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6)
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4)
6)
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3
5
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3
5
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u
V
0
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I
U
w
/
\\
8.15
0
6
- Inverter
2
current switching
4
sequence)))
\"\037
I
/.
(...-\"(\037
0
4
.\"\\
V
....
-
....
...-
W \\ \\
Figure
of the
control.)
useful
Inverter is switching
period
half-cycle
is obtained.
The switching pattern for the
thyristors varies over the frequencyrangewhich
a complex
computer program for converter
requires
that
and decreased from)
be increased
a
frequency
Figure
frequency
within
sinusoidal AC input. By connecting two similar
converters backto back in each line, an AC output
a cycloconverter
output range of a cycloconverterto a multi-pole
motor. Power regeneration from the
synchronous
motor
back into the main
is available.)
power
supply
A
to maximum
zero
Cycloconverter
6
2)
N
(
'--
S
J (I
Electric
There
windings
is no connection betweenthe three motor
the line converters have to be
because
isolatedfrom
obtain line
each
other
commutation
to operate
(natural)
The
converters
may
but it is more
HV line,
additional
thyristors.)
prospective
reduces
the
level
while
to limit
line impedance
fault
and
current
distortion at the main
157)
Voltage
be directly supplied from the
usual to interpose step-
down transformers.This
and its required insulation
correctly to
of the
switching
and High
Propulsion
the
harmonic
motor
voltage
providing
size of
voltage
busbar.)
supply
L1
L2
L3)
Bridge
Bridge
Cyclo-Converter)
Bridge
- A
Bridge - B conducting)
conducting)
of a single low
Synthesis
a three-phase
higher
from
(very approximate))
Figure
8.16
-
Cycloconverter
circuit and output
voltage
waveform)))
frequency
frequency
- B)
- A)
158
Practical Marine Electrical Knowledge)
8.6
of the main
arrangement
physical
in the propulsion
system are shown in
related
The
System
Propulsion
components
Operation)
This section describesthe overall operation
of a
and
is
based
on
a
diesel-electric
propulsion system
with synchroconverter
arrangement
In
each 12 MW, 3 kV
example,
has two separate 6 MW stator
this
each
is supplied
winding
transformer
and
half
will
in
propulsion
propulsion
and
windings
of
a static 6-pulse
range
An emergency
the
of 0-29 Hz.)
By using two converters feeding two separate
0
fitted 30 apart,
a 12-pulse
shaft
windings
shaft
vibration.
torque is achievedto minimise
complicated arrangement of supply
transformers
and converters
can produce a
A more
in
brushless
excitation is also obtainedfrom
HV busbars
via a 6.6/0.44 kV static transformer
a thyristor controller, an AC/AC
transformer
rotary
the motor) and a set of
for the final
conversion
diodes
(standby)
static
available,
but
a command
the
signals
,
but
to DC.
the
as shown in Figure
shown)
(not
(set speed) input
and
many
a closed
control
8.19,
receives
feedback
etc),
shaft
loop. The
the size of
are
principal parameters to be controlled
motor stator current (to set motor torque) and the
motor frequencyto set the shaft speed. In addition,)
A third
and controller is
diagram.)
3 x 6.6 kV 60 Hz HV MSB
;
;)
'/
speed
(voltage, current, power,frequency,
main regulating item is the actual
speed feedback forming
shaft-mounted
excitation
supply
is not shown in the
set
giving
port.)
In a synchrodrive
system,
the central processing unit
torque.)
Motor
(inside
telegraph
(dead-slow, half-ahead, etc) is available
control station. The ship propulsion
at each
regulatorand side thruster regulators can be
combined into a master joystick controller to give
for accurate manoeuvring
directional
control
overall
commands
stator
24-pulseshaft
position is determined
propulsion console in the ECR.)
command
on the
a shaft
from
controlled
a switch
by
synchroconverter.The 24-polemotorshave
range of 0-145 rev/min
converter output
frequency
throttle stations for both shafts are
Selection the
from a 6.6/3.0 kV
speed
Control
on the bridge
(in the wheelhouse and
and local (in
room
on the wings),enginecontrol
HV switchboard room) positions.At sea, the shaft
speed commands are set from the bridge and
repeated in the ECR. In port, the control position is
to the ECR. The local control position
transferred
used
for testing
and maintenance duties,
is mainly
but
also
acts as an emergency control station.
Figure 8.17.)
motor
8.18.)
installed
frequency
control. For a largeship, the power
system
employ HV generation, as in the diagram
Figure
,)
I
Propulsion
Power Suppliers)
\037)
dJ)
Harmonic
Harmonic
filter)))
Transformers
filter)
6.6kV/3kV)
Synchronous
controllers)
Field controllers)
Rotary transformers
and diodes
2 x 12 MW, 3 kV
Synchronous motors
o - 145
RPM
\037
Figure
8.17
- HV
propulsion power system)
o - 145
RPM)
.\037
Electric
the DC motor field current has to be continually
via the
controlled from the propulsion
regulator
excitation converter.)
In normal
and
running
full
and
end of the motor
the non-drive
of less than
are derived from
position
to turn off so that
the
thyristors
regain control. The decisionis now
which
and which sequence of switching
thyristor
is required
to maintain the required shaft
direction
It is necessary
of rotation.
to know exactly the
position of the rotor poles and this is provided by
shaft
the
position encoder for low speed, pulse
mode
When
kicked
above
10 0k
converter
speed,
to allow the
to revert to its normal line-commutation
mode for
synchronous
At speeds
If
thyristor
problem
is overcome
is
the
thyristors
the
likely
operation.)
inverter
individual
thyristors
are not
consequences.)
ANSWER)
by pulse mode operation
forced to zero by
If
two
or more
switched
momentarily
circuit fault
controlled rectifier stage. This)
in the
large enough
switched off (commutated)
at the necessary
the
instant, a serious problemarises.Explain
Remember that a thyristor
can only switch off
when its current becomes zero.)
This
will be
QUESTION)
(line commutation).)
wherethe current
EMF
not generate
sufficient back EMFto cause automatic
switch-off
operation.
the motor
on
detectors
shaft.
does
motor
the
10\302\260/0,
159)
can
controller
of each
5\302\2601o
other,
propulsion motor speeds within
mode
the bridge can select a shaft
phasing
synchro
that applies momentary acceleration/deceleration
to bring the propeller blades into an alignment that
vibration
into the hull.)
minimises
shaft
Speed
and High Voltage
allows the inverter
both
with
away,
Propulsion
Reactor
Filter)
I
off
inverter thyristors
naturally,
across
path
coil
I
are unable to be
they will apply
the DC link.)
a full short-
PEM STBD)
AC/DC/AC
Propulsion
transformer)
converter)
Reactor
Propulsion
transformer
coil
I
I
ACIDC/AC
_
converter
Pulse
t)
(YYY)
*)
firing)
DC
field
rotating diodes
\"'C
...
ca
Excitation
transformer)
o
.c
.s::
CJ
:!::
\037
en
r---------\037
I
I
I
I
I
I)
PMS)
.-c
re
ulsion
Pro
! t
!
Bridge
ECR
Local
Excitation
::E
>
:I:)
+
Propulsion
-
AC/DC/AC
I
I
Reactor
coil)
Propulsion
\037
firing)
lA..uJ)
AC/DC/AC
converter
I
Reactor
Filter)
8.18 - Interconnection
Pulse
converter
transformer)
Figure
-)
transformer)
transformer
of main
propulsion
Rotating
transformer)
r 1
t
stations)
Control
ca
-)
ulator
components)
I
coil)
PEM PORT)))
Rotating
transformer
DC field
rotating
diodes)
Marine Electrical
Practical
160
Knowledge)
-.\"'()
..11
',7,)
. ,)
.
'f\"
o)
.-. \".'.)
PMS)
\037 Processorconuolled
Shaft
regulator)
Speed
position)
input)
Current
Shaft speed)
Frequency
I
t
3 x 0 - 3kV;
L
Network
3 x 3kV; 60Hz
Machine
bridge
DCI1nk
47r
0 - 29Hz)
bridge
47r
Controlled
Controlled
inverter)
rectifier
0-145 RPM)
Synchrodrive
Figure 8.19 - Propulsion
scheme)
control
motor
Converter)
For normal running,
above
about
10 % speed,
the operation
is switched to synchronousmode
where
the
in both bridges are switched
thyristors
off
naturally
(line commutated)
by their live AC
voltages from
To reverse
the shaft
rotation,
the
forward/ahead
currents
is
phase sequence of motor
supply
reversed by the inverter
This
reverses
thyristors.
the direction
of stator
flux rotation and therefore
shaft
direction
to astern.
The rate of deceleration
to zero
must
be
speed
carefully controlled before
a shaft
to avoid
reversal
large power surges in the
system.)
For a motor braking
the inverter
operation,
bridge
can be consideredas a rectifier
when
bridge
viewed from the live AC supply producedby
the
EMF.
motor
If
the
network
thyristors are switched with
than
DC
the
90\302\260,
power
flow
from
braking).
(motor
and
Overall
system
PLC-based
that
effectively
supply.)
angle
bridge
greater
.
Automatic
motors)
.
auto-start, synchronisingand
.
of
control
.
.
.
load
and
for main
limitation
dynamic
propulsion
generators
tripping
of propulsion
motor
acceleration.)
of:
bridges are swapped over.)
.
proposal
.
sharing
performance
running
to start/stop
time
a generator
for generators
motors)
its
sharing
reversing
by preferential
shedding
diesel
with
braking
limitation
power
.
demand
load
manoeuvres)
Load
power
propulsion
from the
regeneration
motors during
.
coordinates
for
limitation
generators
link voltage reverses, causing
motor back to the supply
In this mode, the roles of the
power control is provided by a
power management
system (PMS)
power
standby
Monitoring
the
machine
network
(rectifier)
a delay
are:)
PMS functions
the
Control of:)
motor.)
and
supply
Broadly,
.
status
and data display
.
safety
performance.)))
and propulsion
of
Electric
Harmonics)
8.7
The input
as
to a static
current
generallyhas a
power converter
content
harmonic
high
due to
result
and
waveform,
which
additional
heating of other equipmentconnectedto
the
system.)
may
in
the
malfunction
are shown
in
synchroconverter
8.20.)
Figure
Harmonic frequencies are generallyinteger
3, 5, 7, 11, 13, etc) of the fundamental
multiples
(eg
th
in
(supply) frequency. Therefore, a 7 harmonic
420
Hz
of
a 60 Hz AC voltage has a frequency
of 660 Hz. Harmonic
and an 11th has a frequency
the
of the
reciprocal
amplitudesare roughly
particular shape of the
depend
harmonic
voltages
supply
etc. The
voltage
will
causing additional
supply reactance
in the
(inductive and/or capacitive).See the
Figure
14.3%
currents
harmonic
on
resulting
fifth,
example
in
8.21.)
The 300 phase shifted transformers
effectively
drawn
double the current
pulses
by the motor, so a)
Figure
8.20
that
harmonics
converter
- Waveforms
Motor cu\"ent)
cu\"ent)
for synchrodrive
converter)
are a
harmonic
significant
actual
with
an
17 th .)
can be examined
waveshape
or calculated into its harmonic
voltage
oscilloscope
with a harmonic/spectrum
analyser. To
necessary
level of voltage
in a non-sinusoidal AC supply, it is
to use true rms (root-mean-square)
indicating
instruments.)
the useful
measure
accurately
current
of the AC input to a
also
has componentsthat are
synchroconverter
related
to the motor operating frequency.The DC
link reactor
coil reduces the ripple in the link current
so that the effect on the AC supply side is reduced.)
The
content
harmonic
The total
heating
effect
of distorted
(non-sinusoidal)
current waveform
is calculated
from the rms
sum of all harmonics
the
fundamental
including
st
1
t
otal
rms
value
is:
(or harmonic),
eg
I == .J /\037+ /\037+ /121 + /1\037 for a waveform
Some harmonics are eliminated
by careful
system
more
circuit
inductance,
using
design, eg by adding
phase shifting transformers (star/star and star/
the converter
pulse number.
delta) and increasing
Idealised
the
transformers,
The
or
harmonic number, ie 20% (1/5)for the
for the seventh, 9.1% for the eleventh,
all
cancelled.
That
multiple of 3 are also automatically
leaves
harmonic numbers of 5th , 7 th , 11 th , 13 th , 17 th ,
etc as potential problems. For a pair of 6-pulse
supplied
synchroconverters
by a pair of phase
content
for a 6-pulse
AC system,
three-phase
th
th
problem is reducedto the 5 , 11 and
(eg synchroconverter, cycloconverteror PWM).)
waveforms
point.)
supply
For a generator sinusoidal
AC voltage
waveform
and
positive
negative shapes, all
even-numbered
harmonics
are cancelled out. In a
shifted
The size and frequenciesof the harmonic
currents
and voltages depend on the converter
method
of control
and
type, the pulse number
Typical
161)
appears to be 12-pulse
system
the
from
viewed
Voltage
with identical
from
is switched
the way the current
(chopped)
currents
are
to
Harmonic
important
phase
phase.
distortion of the supplyvoltage
because
they cause
supply
converter
6-pulse
and High
Propulsion
with three
significant harmonics.)
The % total
from
the
rms
value
distortion
(THD) is found
sum of rms harmonicsto the
of the fundamental.)
ratio
harmonic
of the
Motor
voltage)))
162
Marine Electrical Knowledge)
Practical
\037)
analysis of representing a complex waveform
as separate harmonic sinewaves)
Harmonic
+ 3rd and 7th harmonics)
fundamental
Figure
waveform as the sum of
overall
Approximate
8.21 - Harmonic analysisof
waveforms)
Most ship Classification Societies demand that
the
of the mains voltage is
in
than
but
100/0,
QUESTION)
440 V,
A distorted
60
waveform
Hz voltage
practice
is found to includeharmonicsof:
20%5
th
the
Determine
and
voltage
the
this is usually less than
ANSWER)
The
circuit.
series/parallel
5 th harmonic
17th harmonic
is 26 V.
The overall rms value of
VH ==
(damping)
of 440 == 88 V
is 40 V and the
is 20%
the 11th harmonic
Similarly,
(R) is included
is 440 V.
level
.J 88
2
+ 40
the
2
three
+ 26
2 ==
harmonics
100
is)
V
to a
tuned
resonantly
rms
it is
to the
troublesome harmonics.The filters are combination
sets of inductance (L) and capacitance (C),each
rms size of each harmonic
overall THD.)
The 1st harmonic
5%.)
To minimise the size of voltage
distortion,
that
are tuned
necessary to connect filters
th
60/0 17 .)
11 th; and
90/0
;
less
THD
to
act
particular frequency in a
Additionally, some resistance
as a harmonic current limiting
effect.)
The simplestway to view the overall system is
to considerthat the converter
injects harmonics
while the filter
absorbs
them.
Filtering
is not perfect
over the variable frequencyrange,so while the
harmonic
is not completely solved, it is
problem
minimised.)
So the
THD == 100/440
== 0.227
per
unit or 22.70/0)
Practical
harmonic
installations
are physically
large and will
and heat in the
components.)))
create
in
power
power
systems
losses
Propulsion and High
Electric
A cycloconverter
drive employs complexthyristor
to create
a variable low frequency output.
switching
The
associated
harmonics
range is wide, variable
and
difficult to predict, so static filtering
is difficult.
With large cycloconverter drives (eg on a
it is usual
to employ a pair of motor
ship),
generator
cruise
(instead of transformers) betweenthe 6.6 kV
and
440 V switchboards.
This arrangement provides
a clean(harmonic-free)
that does not
supply
to the LV side due to
transmit HV voltage
variations
the rotational mechanical inertia of the M-G sets.)
visible light,
which
has
pass through
the
door
a short
163)
Voltage
wavelength, can
but microwaves,
a
with
wavelength,
cannot). Apertures can occur in
door
ventilation holes, spaces for
fittings,
gaskets,
on boxes, cable entry and exit
seams
instruments,
longer
points,etc.)
sets
LV supplies
clean
Where
Hz and
110 V,
ocean survey
ships
50
are essential (eg 230 V,
instrument power on
DC converters),
it is usual
Hz for
60
with
separate diesel generator sets for that
In this case, the main
purpose.
power
system
would probably not employ harmonic filters
but
is
likely to use capacitive voltage \037urge suppression
to minimise
over-voltage spikes on the main
to provide
busbar
electrical
source
problem of interference(noise)
is how to minimise it at
limit
its
(Consider
caused
by
reception
electric
power
which is often
ideal and allows leakage of radiation
from
effective
apertures caused by the braid knitting,
and
at either end of the screen/
by the connection
armour. The more expensive screened/armoured
from
far
the
cables
better
a
have
and are preferred,
coverage
armour
be negated
termination.)
8.8
Propulsion
can
effect
the
but
into adjacent
transmission
by
poor
screen/
and
Auxiliaries
bike
motor
and its shaft
motor
propulsion
bearings, converters,control
that must be continually
heat
generate
regulators,
coils and harmonic filters
reactor
transformers,
the interference
to TV
the nearby operation of an
tool or unsuppressed
electric
The
susceptible equipment to prevent circuit
malfunction.
cables,
Protection)
systems
and/or
armoured
and
is the coverage
for interference
issue
important
screened
of
supply.)
The general
in
An
all
removed
by auxiliary
cooling services. An overtemperature
condition
must be managed by load limitation
or
disconnection.)
ignition.))
The coupling
devicescan be
inductive
electric
(magnetic),
electrical components are
air or by forced air/
by forced
In a large propulsion motor,
circulation.
High current
between source and reception
cooled
generally
or conductive (directly through
All of this is the subject of
the
conductors).
or EMC, which
electromagnetic
compatibility
is a complicatedanalysis
due
to the wide
water
range of possibilitiesfor interference
coupling.
Manufacturers
of electrical/communication
equipment have to test their designs to prove and
a freshwater
(capacitive)
declare acceptablelevels
of
see
an internal
8.22,
Figure
circulates
air through
This air is forced by
compatibility.)
the
cooler,
which
machine,
main
the
electric
fan
shaft-mounted
and stator spaces.
fans to flow through
rotor
usually mounted on top of
removes the heat into the
cooling system.
rated as I P56
typically
The motor enclosure will be
up to the shaft line, and I P44
above.)
filtering and circuit screening are two
interference effects, but no
method can be perfect. The most important
single
factor
that compromises
a screen performance is
its
of the ci rcu it.)
coverage
Harmonic
of limiting
methods
of radiated
noise as visible light. A light
bulb that is enclosed in a full metal box with
no
holes
or gaps in any of the seams ensures that
no light escapes
from the box. If any holes exist
in the
box for cable entry/exit or the box
Think
are
Stator
are
winding, cooling air and water temperatures
for display
in the ECR. It is essential
monitored
and hot spot temperaturelimits
that general
exceeded.)
QUESTION)
Which major feature of an electrical
principally degraded by overtemperature?)
machine
seams
not
amount
perfect
then
of energy that
the maximum
linear
light energy
will
escape.
The
can
on
escape
depends
dimension
(L) of any aperture
and the wavelength
(A) of the radiation
(which is
the principle used in microwave
oven
doors where)
not
are
ANSWER)
The
around the stator and rotor
HV machines are generally
Large
insulation
windings.
insulatedwith
normally
class
operated
F materials
but will
well below this limit.)))
be
is
164
Marine Electrical
Practical
Knowledge)
Air/water
Cooling
heat
exchanger)
fan motor)
Cooling
fan
motor)
-)
PEM 12 MW
145RPM)
'\
'\
.)
.)
Figure
-
8.22
Propulsion
motor construction
I)
I)
I)
outline)
Insulated
waterpipes)
A
\\
.( \\
..,.. .
(
.,-..'
.'
\037
-
G
K)
water cooled double sided
heat
sink clamped
to thyristor
air or
Forced
metal
alloy
anode/cathode
Figure
8.23
-
Thyristor
cooling arrangements)
faces)))
Propulsion and High
Electric
internal
electric
Large motors and generators have
heaters
that are activated when the machineis
The
is to raise the
requirement
internal
to about 3\302\260C
above
ambient,
temperature
which will prevent
condensation
settling on the
motor insulation.
an anti-condensation
Typically,
heater rated at about 4 kW at 220 V would be fitted
The metal
converters
in
the
A
perfect
it
so
A
thyristor,
closed
sinks
heat
alloy
connectionsto anodeand
In particular,
to temperature.
sensitive
Why?)
ANSWER)
and at a high
Semiconductor componentsare particularly
temperature of large
purity.
high
exceptionally
sink cooling must be of
for heat
used
water
The
HV machine.)
large
current
switching
the
of
thyristors
the
water
level.
Insulated,
plastic
and the electrical resistance
must be extremely high
to avoid
voltage
used
is
piping
form the electrical
so are live
cathode
accidentally
connecting the adjacent thyristors
via the cooling
medium.)
must be carefully managed.
switch has no voltage drop
across
loss is zero when conducting.
a small voltage drop
however,
develops
its power
The instrument
similar to that
conducting its current.
an average
current of, say,
Fora thyristor
carrying
2000A, its power loss could be up to 4000 W,
which
would
rapidly destroy the device unless the
(typically
internal
to 2 V) when
up
The heat sinkis itself
forced
cubicle,
A more
cooled
by clean
is circulated through
air filters and an air/water
air that
and
Protection
that
converter
heat
exchanger.
effective method is to pump demineralised
fresh water directly through
the
heat sinks
thyristor
and then circulate it through
an external
water/
water heat exchanger.)
rise
(di/dt)
limiter)
they
switching.
than
5 J.lS
of electrical
are
operated
power componentsrequires
their normal current,
Figure
8.24 shows
Voltage
thyristor
rise
(dv/dt) limiter
or 'snubber')
Inductance
coil)
or
effect
inductive
from
ferrite
around
rings
conductor)
Gate control \0371
circuits)
- . . .\".,.
Set
8.24
-
Thyristor
protection components)))
input
for
within
c)
R)
Current
of less
case
voltage and temperatureratings.A special
arises for the protection of large
semiconductors,
eg thyristors, which can be destroyed by a fast rate
of change of voltage and current caused by rapid
dry
the
units
Conductivity
of micro-Siemen
(J.lS)
If the set conductivity
limit
is
thyristor cooling duty.
the test instrument will alarm
and trip
exceeded,
conditions, depending on the severity of the fault.)
removed.)
is efficiently
heat
is
in a salinometer.
values
acceptable
the conductivity
to measure
used
used
is measured in the
with
Figure 8.23 shows how large power thyristors are
heat
sinks
that
clamped between large area metal
conduct the internal
heat
from the device.
away
Figure
165)
QU ESTION)
disconnected.
in a
Voltage
value
-t)
protection.)
Marine Electrical
Practical
166
rise (dv/dt)
a rapid overvoltage
an R-C snubber circuit
To
suppress
a thyristor,
action is based on the fact
seriesresistor
the
limits
that
across
voltage
limit
for the
protection
of relay
their
tripping
thyristors.)
times
are critical to the circuit
under
fault
protection
conditions. Such settings have
been
very carefully
matched to the circuit and its components.
Confirmation
of protective
testing
relays requires
which
injection,
calibrated current
and
voltage
is generally regarded as a specialist
task
for an
outside contractor. Testing is normally
performed
during
a major
survey during
8.9
High
Voltage
a dry-docking
period.)
main
an
relationship
current
is reduced
size (for a given
power)
regional
power
distribution
that
as
and
The main
maintainer,
the very
disadvantage
when
working
industrial
perceived by the user/
in an
HV
installation,
necessary adherence to stringent safety
is considered
as HV. For the purposes of)
and
Each
breaker
phase of a vacuum circuit
contactor
consists of a fixed
and
moving
within a sealed, evacuated envelope of
an LV
For HV, the
or
contact
borosilicate
glass.)
an alternating current is interrupted
contacts, an arc is formed
When
the
separating
metal vapour
from the material
on
and this continues to flow
by
by
a
contact
surfaces
until
a current
zero is approached in the AC waveform.
At this
a region
of high
instant, the arc is
by
dielectric strength that is capable
of withstanding
a high recovery
Most of the metal vapour
voltage.
condenses
back
on to the contacts and is available
the
replaced
arcing. A small amount is
placed around the contacts, which
insulation
of the enclosure. As the
deposited
subsequent
shield
the
the
Because
interrupter
wear.)
less
of its very short contact travel,
has the following
advantages:)
.
Compact
quiet
.
minimum
maintenance)
.
non-flammable
a vacuum
unit
and
8.25,
life of the unit
The
but
dashed
line
an HV
switchboard.
main
non-toxic.)
is
procedures.)
In the
ship's
power network shown in Figure
all of the equipment indicatedabove the
between
difference
is at the HV
considerably
drives.)
motor
and Contactors
Breakers
arcing period is very short (typically about 15 ms),
the arc energy is very much lower than that in air
break
circuit breakers,
so vacuum contacts suffer
the voltage is increased.Working
at high
voltage
overall
size and
significantly reduces the relative
of
weight of electrical powerequipment.HV levels
3.3 kV, 6.6 kV and 11 kV are regularly employed
ashore for
Further distribution
to interconnect with the emergency
circuit breaker types may be air break, oil break,
or
gas break using SF6 (sulphur
hexafluoride)
vacuum
break. Of these types, the most popular
and
reliable
are the vacuum interrupters, which
also be used as contactors in HV motor
may
starters
(see Figures 8.25, 3.20 and 3.21).)
on
electrical power demand will
HV installation. The design benefits
relateto the simpleOhm'sLaw
440 V switchboard.
are
protects
require
propulsion,
the
for
on Ships)
a large
with
Ships
generators,
and
system
parameter level (overcurrent,
undervoltage, etc) and
HV
(for
feed
The
operation.)
settings
the
motors
HV
part of the
and air conditioning
compressors)
the step-down
power transformers, which
HV Circuit
Circuit protection for the electric propulsion
units
(including excitation and harmonic filters)
principally
coordinated
employs
protective relays that monitor
earth leakage and temperature.
current,
voltage,
See Chapter
2 for protective
relay functions and
The
supplies
made
switchboard.)
the thyristor.
change of current
(di/dt)
through
Special fast-acting line fuses
may be used as
backup overcurrent
equipment.
links
rate of
the
the
for a
system
integrated
side thrusters
the
while it is limiting
surge through
capacitor
the voltage across the thyristor.
heat
Significant
will be produced by the resistor
which, in some
is directly cooled by a water jacket.)
applications,
An in-line inductive effect will
field
LV
From
HV
network
overall
current
corresponding
the
includes
this
safety,
propulsion motor as it is an
Its
cannot
used.
is
across a capacitor.The
instantaneously
change
Knowledge)
In
could
the
be
circuit
gas-type
separated
in
is governed
by contact
erosion,
up to 20 years.)
an
SF6
breaker,
(sulphur
the contacts are
gas
hexafluoride)
at a sealed pressure chamber at
or 5 bar (when tested at 20\302\260C).)))
that
is typically
500
kPa
Electric
8
g
DE1
DE2)
DE3)
167)
and High Voltage
Propulsion
DE4)
o
o
\037
QY)
3 x 6.6 kV 60 Hz HV MSB)
rn)
M)
AE)
6)....)
\037)
\\
,
PEM 1)
I)
PEM2)
/)
\"
'.....
.....-
HV)
---.......---.-----)
\037
,
--------------
\037-=I
3 x 440 V 60 Hz LV MSB)
I-
---
\037.,
I\037
-------)
LV)
EDG)
M
M
M)
J
--L--..L
L)
3 x 440V 60 Hz ESB)
3 x 220V 60 Hz ESB sub)
Figure
8.25 - HV/LV
supply
power
system)
Insulation
HV
QU ESTION)
Some HV
have
systems
hull
point of a
via a neutral
is this
connection
the neutral
generatorearthedto the ship's
earthing resistor (NER).What
for?)
The HV
HV windings
with
V
PH
and
of earth
size
the
(zero resistance)
== 6600/--J3
in
fault
earth fault
causes
a 6.6
== 3810
kV system
with
a 200
LV
materials.)
are generally
for transformers
epoxy
for
those
quartz
resin/powdered
free,
and
resistant
humidity
tropicalised.)
a
Conductor insulation for an HV
more complicated design than
(2
V)
LV
type.
== 19 A.)
E/F current is 3810/200
However,
HV
conductors,
space
and
Where
the
live
the maximum
is maintenance
that
current.
a generator phase winding,
is V PH/RNER.)
across
short-circuit
so the fault current
example,
NER, ER,
an
to
material
compound. This is a non-hazardous
ANSWER)
For
for generators,
arrangements
winding
insulated
A hard
Requirements
transformers and motors are similar
for the need for better insulating
except
The
To minimise
M)
parts
terminal
distances
cable
is
requires
necessary
a
for an
less copper area is requiredfor
which allows a significant saving in
weight for an easier cable installation.
is air (eg between
metal
insulation
switchboards
and in
and earth within
bare
boxes) greater clearance and
are necessary
in
HV
creepage
equipment.)))
Practical Marine Electrical Knowledge)
168
be suitable to
of a 6.6 kV
integrity
test
megger
determine the insulation
Person - An Authorised
Person
is
by
appropriately trained and appointedin writing
the Superintendent/Electrical
Engineer to carry
out work as permitted
by these Rules.)
\"Authorised
motor?)
ANSWER)
give a rough guide to the I R
but at 500 V, the tester
is not properly
For
6.6 kV equipment,
stressing the insulation.
5000 V IR tester is required.)
No.
It
it
defines
a 500 V
Would
or authorised persons, which
by competent
as:)
QUESTION
Person
is
Competent Person - A Competent
technical
appropriately trained and has sufficient
would
value
a
or experience
to enable him to avoid
It is the duty
of the Authorised
Person
knowledge
danger.
issuing a permit to work covered
by these Rules
are competent
to
to satisfy himself that persons
\
carry out the work involved.
8.10
Safety)
Voltage
High
with any
contact
personal
Making
electric
At high voltage
voltage is potentially
dangerous.
the electric
shock potential is
(> 1000 V) levels,
lethal. Bodyresistancedecreaseswith increased
flow.
level, which enhances the current
voltage
Remember
that an electric shock current
as low
as 15 mA can be fatal.)
footwear,
and certified safety clothing,
and a hard hat should
may arise from arcs, hot
approved
Appropriate,
protection
eye
be usedwhere
danger
surfaces and high
etc.)
voltage,
No work should be carried out on high voltage
installations or equipment unless that equipment
\"(a)
is:)
Dead
Isolated and all practicablesteps have
to lock off live conductors,
taken
(b)
been
transformers
voltage
that
conductors
may
attached in English
(d)
Released for
to
(e)
HIGH VOLTAGE!)
- HV
warning
The risk to people
minimised by the
national
industry,
notice)
in
HV
'Code
diligent
application
and international
of company,
safety
for this duty.)
of Safe Working
Practices for Merchant
Seamen (COSWP)',
2010,requires
on HV equipment
The
caution notices
any other
by the
work
issue of a Permit
Sanction
for Test.
Person
designated
Competent
working
to carry
out the work fully understands
the nature
and scope of the work to be carried out
and has witnesseda demonstration
that
the equipment/installation
is dead at the
point of work\".)
should only
be
2010)
is greatly
areas
guidelines, regulations and procedures. Personnel
are
to routinely test and maintain
required
HV equipment
should be trained in the necessary
as
practical safety procedures and certified
The
or a
Work
and
COSW\037
working
who
qualified
live.
vessel.
of the
language
8.26
become
and
supply
Voltage
High
Figure
where
Earthed at all points of disconnection
of
(c)
DANGER
(except
are bolted)and dead
the connections
that
work
carried
out)
The access
to HV
must be strictly
scheme
and
switchboards
controlled
by using
equipment
a permit to work
and isolation procedures
(PTW)
line tests and earthing down
with
live
work
is started.
COSWP
requires that)
t\037 Limitation
of Access
instruction
used to give
written
instructions
of work
to be carried
of but NOT on High Voltage
limits
Installations.
together
beforeany
\)
should be
defining the
out in the
Equipment/
vicinity
Electric
and procedures
The electricalpermit
requirements
in any
access
are similar to permits used to controi
hot work situation, eg welding, cutting,
etc,
burning,
in a potentially hazardous area.)
has been
suspension
work.
Finally,
usually
All
carried out on HV
to be
work
equipment
Some marine
work
to
The format
of
will
vary
for different
and organisations. COSWPChapter 16
of PTWs for general electric
examples
provides
work
and
for HV electrical work. These are included
in Appendix
1 of this book.)
companies
have
notices
caution
been
signed as authorised
test
also provided in Appendix
Before
equipment
the
Electrotechnical
'\\.
.)
.,. ..)
': \037\037.
Insulated
Figure
8.27
LED indication)
- HV live-line
testing
extension
rod)
components)))
testing.
COSWP
is
or
be tested
and
disconnection
by
using
checked
known
HV
battery-operated
test
Officer
the
source
either as a separate
(supplied
or included
as an internal
self
unit
facility).)
Two people, competent in treating
should always be together when
equipment.)
\\.........)
. I: \
with live-line
also
isolation.
an approved
live line tester as shown
in Figure
8.27. The tester
itself must be proven
before
and after such a
test. This is
the tester
to a
by
connecting
'(110,
tester
such
from
down the particular circuit
earthing
in the
declared
it must
PTW,
and proved dead after
(ETO) or Chief Engineer.In the third section,
person responsible for the work (as named in
are satisfied
section
they
one) signs to declare that
HV circuit)
with the safety precautions and that
the
HV
will
1.)
This can only be carried out
applied and where danger/
been displayed. The permit is
by
companies
has to be removed during
generally
A copy of a sanctionto
format
with the first stating
the
at
least
five sections,
work to be carried out. The next sectionis a risk
assessment
where electrical isolation
declaring
has
offshore
electricaltest (eg an electrical
insulation
test) is to
be applied. This is necessaryas the circuit earth
a
Before work is commencedon HV equipment,
PTW must be issued. This permit
is usually
the
last stage of a planned
maintenance
task that
has
been
discussed,
prepared and approved by
officer to be carried out by the
the
authorising
responsible
person. The carbon-copied permit,
person, usually has
signed
by the responsible
and earthing
and
'electrical isolation certificate'
to
and record
declare
exactly where the circuit
isolation
and earthing
has been applied before
the PTW can be authorised. A 'sanction to test'
certificate
safety
may also be required when an
(PTW)
a permit
last
an associated
require
Permit
section
cancels the permit by
authorising officer.A PTW is
valid only for 24 hours.)
the
from the
is
to a PTW.)
subject
169)
isolated and earthed. Sectionfour relates
or completion of the designated
to the
a signature
and High Voltage
Propulsion
electric
working
shocks,
HV
on
Marine Electrical Knowledge)
Practical
170
COSWP
Down
Earthing
Before work can be allowedto commenceon
HV equipment,
it must be earthed to the hull and
dead
proved
by an authorised person.)
advice when
the following
provides
earthing:)
shall be applied and
Earths
Main
\"Circuit
removed by an Authorised Person, or by a
person Competent do so in his presence and
only
As an example,considerthe
at an
arrangements
HV
to
earthing
switchboard.
earthing down method is of two
Circuit
or
incoming
by
types:)
Earthing
the live supply, an
feeder cable is connected
switch to connect all three
This action then releases
from
disconnection
After
the
Here,
outgoing
a manually-operated
conductorsto earth.
a permissivekey to allow the circuit breaker to
be withdrawn
to the TEST
position. The circuit
breakercannot be re-inserteduntil the earth has
been removed and the key restoredto its normal
Busbar
Earthing
on a section of the
busbars, they must be isolated
electrical
sources. This will
section or bus-tie
incomers,
When it is necessary
HV switchboard
all
possible
include
generator
breakers and
on that
out
at
to work
transformers
section.
busbar
(which
Earthing
back-feed)
permissive
key exchanges.
the application of a busbar earth
circuit breaker, which is
special
earthing
inserted
into the switchboard
solely for
In
some
installations,
is by a
temporarily
the busbar earthing
For
extra
duty.)
confidence and operator safety,
additional
be connected locally to the work task
portable
approved
earthing
straps
and an
earth
the
of an
to always connect the common wire
Remember
to
use, to prove it is in good
after
and
before
working order.)
Where practicableCircuit
applied through
a circuit
Main
shall
Earths
be
or earthing
breaker
Beforeclosingto earth,
the
trip features
unless
shall be rendered inoperative
the
circuit
After
closing,
impracticable.
shall
be locked
features
rendered
notice
attached.)
in
the
earth
position
inoperative
with
this
is
breaker
and the trip
a caution
Earths may be appliedat the point of
the issue of a Permit to Work by the
of the work.)
Competent Person in charge
Additional
work
after
Circuit Main Earths/Additional Earths may
at the point of work
be removed/replaced
of a Sanction for Test by the
after
the issue
Authorised person conducting the test.)
also
insulated extensiontool, eg at the terminals
HV motor, as shown in Figure
8.28.)
to
When High Voltage Equipment/Installations
the
have been madedeadand Isolated,
to be Earthed shall be proved
Conductors
if practicable
Dead
using an Approved potential
should be in
indicator
indicator. The potential
and be tested immediately
date
for calibration
can
earthing
with
instructions.)
down is carried
compartment after
breaker
a bus-section
could
the
satisfying
his
switches.)
position.)
from
to
first
before
three-phase
the earthing
straps,
connection last.)
the other wires
When removing
the earth
remove
connecting
connections.
always
A Circuit
work
may
at a time
Main Earth applied at the point of
and replaced one phase
be removed
the work provided this
to facilitate
instruction is recordedon the Permitto Work.
Earth
connected
If this is the only Circuit Main
to
to the apparatus, then a person Authorised
to Work shall remain at the point
issue
Permits
of all
the
for
of work and be responsible
safety
those engaged in the work whilst the Circuit
Main Earth is removed.No other simultaneous
work shall be permitted on any part of the circuit
during
the
validity
of this Permit to Work.\
COSWP
Section
22.15.11)))
Electric Propulsion and High
Phase connection
*-)
universal
_.
-.
. ')
\"-
clamps)
..
---
........... .\037)
171)
Voltage
,.)
\037
*
Highly
.)
flexible,
short-circuit
leads
made of E-Cu with
transparent
plastic
sheath)
Connection piece with
c*)
kinking
waterproof
protection)
\
Earth connection clamp)
Figure
8.28 - Portable earthing
connectors)
8.11
QUESTION
Why is earthing
during
HV
down considered essential
equipment
accidentally
the
Voltage
Equipment
Testing)
maintenance?)
The HV (eg 6.6 kV) installation covers the
generation,main supply cables, switchgear,
ANSWER)
So that
High
worker
can
be assured
that
the
himself) cannot experience any
because the earth
applied
voltage
(and
connectionbondsthe circuit
to
earth
(zero
volts).)
electric propulsion (if fitted)
transformers,
a few large motors, eg for side-thrusters
and
and
air conditioning compressors. For all electrical
the key indicator to its safety and
equipment,
condition
is its insulation
resistance
general
(IR)
and this is particularly
so for HV apparatus.
The IR
must
be tested
periodically between phases and
between phases and
earth.
HV equipment
that)))
Marine Electrical
Practical
172
is well
and operated within
maintained
designed,
Knowledge)
should have
and temperature
power
ratings
useful
insulation
life
of 20 years.)
its
a
An IR
test
is applied
with a high
DC voltage
that
applies a reasonable stress to the dielectric
material
For 6.6 kV rated equipment, a
(insulation).
periodic5000V DC
resistance
insulation
(megger)
test is recommended.The IR test should be
and
corrected
applied for one minute
temperature
to a standard of 40\302\260C. The minimum
IR value is
usually recommended as (kV + 1) MO, where kV
the
voltage
equipment
7.6
eg
rating,
for a 6.6
machines
insulation, an IR
with healthy
may indicate
For
Large
currents
result
cables,
machine.
test
test.)
IR
is
be
a value up to 100times greaterthan
minimum.)
recommended
the
kV
be
earth
must
applied and recorded.The safety
is disconnected.
reconnected
before the IR tester
This safety routine must be appliedfor each
separate
MO would
an acceptable IR value
connection ON. The safety earth may be applied
a switch connection at the supplycircuit
or by a temporary earth connection
breaker
localto the test point. This is to ensure that the
never touches an unearthed conductor.
operator
With
the
IR tester
connected, the safety earth
is disconnected
(using an insulated extension
for the temporary
tool
earth). The I R test is then
through
will
(the polarisation
insulation
value
index
may be
or PI) is usedwhen the
an annual
suspect or recordedduring
survey. The
PI value is the ratio of the I R result after 10 minutes
of testing (R 10 ) to the value recorded after one
minute
PI
class
For
PI
value
materials, the recommended
is 2. To apply a PI test
over a 10 minute
period requiresa speciallRtesterthat has a
motor-driven
generator or an electronicconverter
poweredfrom
a local
220 V AC supply.)
main
switchboard
for
be
with similar
to be satisfactory. A
or compared
is known
that
is not suitable as it will only drive
low
test circuit. A special
ohmmeter
normal
the
through
tester, or micro-ohmmeter, (traditionally
a calibrated
must be used. It drives
a ducter)
called
F insulation
in the
recommendations
equipment
resistance
= R /R
10 1
windings,
contacts
resistance
example, the local continuity
may
measured and checked against the manufacturer's
a few mA
(R 1 ):)
breaker
circuit
rise due to FR resistive
a temperature
Where overheating
is suspected, at a
cause
heating.
boltedbusbar joint
A more involved I R test
machine
through
flowing
busbars and main
the circuit while
the circuit. The
VII and displays the test
busbar
joint, a continuity of a
current (usually I = 10 A) through
measuring the volt-drop
meter calculates R from
result.Fora healthy
few
mO
(V)
across
be expected.)
would
The condition of HV insulation
is governed by
factors such as temperature,humidity,
surface
condition
and operating voltage level. Be guided by
the
manufacturer's
recommendations
when testing
it is difficult and unsafe to
supply. Unfortunately,
of internal
closely observethe on load operation
and maintaining
components
HV
insulation.)
less
developed to make interpretation
sensitive
to temperature.
PI is the ratio of two IR at
two different times. The temperature of the winding
does not rise during
the
10 minute test period so it
PI was
to assume
is fair
that
both
R 10 and
R 1 are
measured
same winding
The temperature
temperature.
correction factor will then be the same for both
cases and will be cancelled
during the calculation
at the
of PI. Therefore,PI is relatively
insensitive
to
temperature.)
Before applying
an IR test to HV
its
equipment,
supply must be switchedoff, isolated,
confirmed
dead by an approved live line tester and
power
for complete
then
earthed
with
the current
safety
in
accordance
PTW regulations.)
The correct procedureisto connect
the
IR tester
to the circuit under test with the safety
earth)
Normally, the safe testing of
that it is disconnected
requires
by temperature
infrared
camera
The
enclosures.
HV
within
resolved
HV
equipment
from its power
This
measurement
is partly
with
an
recording from a safe distance.
the
is used to scan an area and
camera
image is then processed by a
to display hot spots and a
recorded
infrared
computer
programme
thermal
profile
internal
components,
across
recordingcan be made
the equipment.
To examine
busbar joints, a camera
after the
immediately
eg
equipment has been switchedoff and isolated
in accordance
with
a PTW
safety procedure.
some
essential
equipment,
eg a
Alternatively,
can be monitored on line using
main
switchboard,
enclosure
windows
specially fitted and approved
are
suitable for infrared testing. These windows
small
with a permanently fixed steel
apertures
the camera
can view the
meshthrough
which
from a safe position. An outer
internal
temperatur\037
mesh
maintains
steel
plate fixed over the window
normal
the overall enclosure performance during
operation.)))
Propulsion and High
Electric
173)
Voltage
LocavonRdenvficavon
6.6 kV main board
Gen 2 breaker
Copper busbars
Area:
Equipment:
onent:
Com
08/01/13/15:45)
Date/Time:
Fault
and recommendation
diagnosis
Copper temperature
much higher than
Check
tightness,
Conventional colour photograph)
on middle
phase
bars.)
adjacent
copper connections for
clean and re-check)
100 _ __)
\302\260C)
80)
Line 1)
80)
\037\"
WI')
60
po 1)
60
40)
line profile
Thermal
Temperature \302\260C
Label
40)
20)
Spot 1
55.2
Spot 2
100.3
1: max.
Line
99.0
Line 1: min.)
Reference
50.6)
Temp. scale)
Figure 8.29 - Infrared
thermal
image
testing)
to match
simultaneously
image and both
Such
contractor who
contacts.
used
advice to the
proposerecommendation/repair
Any
weakness
in the
in the
interrupter
of the vacuum
the infrared
as part of a test report.
performed
usually
by a specialist
will prepare
the test report and
are
is
testing
image)
photograph of the equipment
A conventional
is taken
Infrared
ship
be
detected
the
display
(SF6)
HV circuit
of the
and
camera
an infrared
Figure 8.29 shows results from
In this
test on a busbar connection.
test,
particular
the camera recorded hot spot temperatures
up
0
to 100 e and the report recommended that the
connection
was checked for tightness as
copper
on the
it was
running
very hot compared to that
copper work.)
neighbouring
be arranged to initiate
an
switches fitted
switching
type circuit
breaker
The tester
impulse
test.
voltage
pulse,
circuit, that
integrity
requires
of typically
is connected
of an HV vacuum
a special high
voltage
produces a short duration
10 kV
across
a 6.6 kV
the open breaker)
for
will
contacts.
to
A falling
each
gas pressures are typically
gas
alarm
chamber. Normal
or 5 bar.)
kPa
Overall circuit protection of
HV
equipment
supervised
protective
coordinated
can
pressure
from pressure
500
by
will
breakers rely on the quality
gas acting as the insulation
operator.)
To test the insulating
strength
as a current flow and the tester
condition
as a pass or fail.)
pressure
between
the
Gas
insulating
chamber
relays.
is
These
must be periodically tested to confirm
their
level
settings
(for current, voltage, frequency, etc) and
their
times. This requires the injection
of
tripping
calibrated
values of current and voltage into the
protective
relays, which is usually performed by
a specialist
contractor
during a main
ship
survey
while
in
dry-dock.)))
Appendix
1
COSWP
Permits
to Work)
16.1.6
ANNEX
-
PERMIT-TO-WORK
Note
The
(i):)
Officer should indicate the sections applicableby
not applicable.
deleting
any subheading
Authorising
next to
headings,
The Authorising
Note (ii):)
Note (iii):
The Authorised
Note (iv):)
This Permit-to-Work
SECTION
A
-
should
Officer
or Additional
insert
precautions are used.
should
Person
contains
the appropriate
tick each
applicable
in the
ticks
lefthand
details when the Sections for
righthand
box
as
they
Other
boxes
Work
make their check.
6 sections.)
of Work)
Scope
Location (designationof space)
Plant
(UNDER 1000 VOLTS))
ELECTRICAL
GENERAL
.......................................................................................................................)
Apparatus/Identification
(designation of machinery/equipment) ........................................................................................................
to
Work
Permit
be
don e (d escri pti on)
issued
to (name of
person
..........................................................................................................................)
carrying
out work
or in charge
of the
work party)
......................................)
Section B - Checklist/Isolation
Data)
Has
a risk
assessment
of the proposedwork
been
carried
out?)
from
the
at the following points
apparatus is dead and hasbeenisolated
system
ri
Des
c
t
................................
.
.
.
.
.
.
...
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .)))
p ion)
(
The above
Marine Electrical
Practical
176
Locks
location
Knowledge)
.................................................................................)
lock set)
and
identify
danger
have
been
taken
been
applied at all
points
of isolation,
TREAT ALL OTHER APPARATUS
AND
Safety
(Detail
fitted
Additional Precautionsto avoid
notices
Caution/Danger
have
AS
AREAS
................................................)
by (Description)
and Safety Signs appropriately positioned.)
DANGEROUS)
............................................................................................................................................................................)
..............................................................................................................................
..........................................
SECTIONC - Authorisin9
of
permit)
precautions
of permit (shouldnot exceed
24 hours)
have been taken and that safety
arrangements
Authorising
person)
of validity
Period
(N
a me ). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
(Sig natu
.......................................................................)
(D ate).
(Ti me)
-
SECTION
D
I accept
responsibility
be made
attempt will
I am
satisfied
of
duration
the
Receipt
for carrying
After
that all precautions
work.)
signing
wherethe work
permit
is
E
SECTION
charge
......................................
. . ....
. . . . . . . . . . . . . . . . . . . . . . . . . .)
out the work on the apparatus detailedon this permit
to work and no
to work on any other apparatus or in any other
area.
charge
have been taken and that
................
.......................................................................)
The work
. .. . .. ..
by me or people under my
(Name)......................................................
Note:
...........
..
........... .......
...
safety
will be
arrangements
Received*/Appl
maintained for the
ied*)
person
Competent
me)
re ) . .. .. .. ... . ... ... ...
work.
of Permit)
Key No.........................................................)
Safety
(Ti
................ hours. I am satisfied
that all
will be maintained for the duration
of the
for
which
.... .. .. .. . ... ... . .. ... ........... .........
(Date).................
.
..
.
.
the receipt, this permit to work should be retained by the person
in charge
carried
out
until
work
is
the
and
clearance
section
being
complete
signed)
- Clearance
been
to work.)))
have
(S ig natu re) ...............................................................
.....)
at the place
of Permit)
this permit to work was issued is now
and all people under my
suspended*/completed*
withdrawn and warned that it is no longer safe to work on the apparatus detailed in this
Appendix 1 COSWP Permits to Work
All work
equipment,
tools, test instruments etc have
(Name)..................................................................... .
.......................................................................
me)
Key No.........................................................)
Safety
F - Cancellation
SECTION
to work
Permit
This
removed.
been
person
Competent
(Ti
177)
of
(Sig n atu re) ...............................................................
(Date)................................. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .)
Received*
/ Applied*)
Permit)
is cancelled.
Authorising Person
. (S n atu re) .............................
(Name).....................................................................
.......................................................................
(D ate). . . ..............
..................................
ig
(Ti
Safety
*
......................................................
me)
Key No .........................................................)
Delete
words
The
not applicable
is
complete*/incomplete*
work
Received*
/ Appl ied*)
and where appropriatestate:
as follows: (description))
..............................................................................................................................
.............................................
................................................................................................................................
..................................................................................................................
.................................
......................................................................................................
..............................
.............................................................................................
...........................
.....................................................................................
..................................................................................
........................
............................................................................
.......................
.......................................................................
....................................................................
..............................................)
............................................................................................................................................................................)
............................................................................................................................................................................)
..............................................................................................................................
..............................................)
..............................................................................................................................
............................................
...........
........
...
......
..... ..... .......... ..... ..........
..................
......
...........
......
.....
....
............
........
............
.................
..........)
.................................................................................................
............................
.........................................................................................
.......... ....................
......
.......
.........
....................
.......
..............
......
.....
.....
..........)
. ...........
... ...
........
.......
..........
..........
..............................................................................................................................
............................................
Electrical
Marine
Practical
178
Knowledge)
16.1.7
ANNEX
PERMIT-TO-WORK
-
ELECTRICAL
VOLTAGE
Note (i):)
The
HIGH
should indicate the sections applicableby
not applicable.
deleting
any subheading
headings,
The Authorising
Note (ii):)
The Authorised
Note (iv):)
This Permit-to-Work
SECTION
A
-
applicable
in the
ticks
lefthand
details when the Sections for
the appropriate
tick each
should
Person
box
righthand
as
they
Other
boxes
Work
make their check.
6 sections.)
contains
of Work)
Scope
Location (designationof space)
Plant
insert
should
Officer
precautions are used.
or Additional
Note (iii):
VOLTS))
Officer
Authorising
next to
1000
(OVER
.......................................................................................................................)
Apparatus/Identification
(designation of machinery/equipment))
to
Work
be done
Permitissuedto
(description)
of
(name
..........................................................................................................................)
person
carrying
out work or in
charge
of the
work party)
.....................................)
Section B - CheckList/Isolation
Data)
Has
a risk
assessment
The above
apparatus is dead and
Main Earths
been
out?
carried
isolated
from the system
have been appliedto the equipmentat the
Safety Locks
(Detail
has
been
at the following points
........................)
..............................................................................................................................
(Description)
Circuit
of the proposed work
location
fitted
and
following
points.
(Description)
..............)
identify lock set) ..................................................................................................
1 COSWP
Appendix
to avoid
Precautions
Additional
notices have been applied
Caution/Danger
APPARATUS AND
ALL OTHER
TREAT
C - Authorisin9
SECTION
of permit
of validity
Period
equipment is dead and
of
at
all points
........................)
AREAS
AS
of isolation, and Safety Signs appropriately
from
positioned.)
DANGEROUS)
permit)
(should not
isolated
179)
danger have been taken by
..............................................................................................................................
(Description)
to Work
Permits
exceed
24 hours)
all live conductors.
............ hours. I hereby
declare
that the
above
Authorising person)
(N
(S i g n atu re) ...............................................................
.... . ... .... ... .... ............
..)
(Date)...............
a me ). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
-
SECTION
D
I accept
responsibility
be made
satisfied
I am
of the
duration
of Permit)
Receipt
attempt will
......
...........
......
.......................................................................)
(Ti me)
for carrying
out the work on the apparatus detailedon this permit
to work and no
to work on any other apparatus or in any other
area.
charge
have been taken and that safety
will be maintained for the
arrangements
by me or people under my
that all precautions
work.)
Key No .........................................................Received*/Applied*)
Safety
Competentperson
(N
a me ). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.......................................................................)
(Ti me)
After
Note:
signing
wherethe work
The work
for
which
charge
been
permit
to work.
work
in charge
the receipt, this permit to work should be retained by the person
carried out until work
is complete
and the clearance section signed)
- Clearance
have
All
equipment,
this permit to work was issued is now
and all people under my
suspended*/completed*
withdrawn and warned that it is no longer safe to work on the apparatus detailed in this
tools,
test instruments
etc have
...................................................................
Safety
at the place
of Permit)
(N a me )...
me)
. . . . . . . . . . . . . . . . . . . . . .)
removed.
been
person)
Competent
(Ti
..........................................
. . ....
(D ate).
is being
E
SECTION
.
(Signature)..............................................................
.......................................................................
.......................................................
(Signature)
(D
ate)
........... ....... .....................................................
Key No .........................................................) Received*
/ Applied*)))
180 PracticalMarine
F -
SECTION
Knowledge)
Cancellation
to work
Permit
This
Electrical
of Permit)
is cancelled.
Authorising Person
.
. (Signature)..............................................................
(Name).....................................................................
(Ti
me)
Safety
*
.......................................................................
(D
Key No .........................................................)
Received*
Delete
words
The
not applicable
is
complete*/incomplete*
work
ate).
............................................................. ... ..... .
and where appropriatestate:
as follows: (description))))
/ Appl ied*)
- ELECTRICAL
SANCTION-TO-TEST
1000
(OVER
181)
indicate
the sections
subheading
not
The Authorising
Officer
should
insert
or Additional precautions are used.
(H):)
HIGH VOLTAGESYSTEMS
VOLTS))
The Authorising
Officer
should
next to headings, deletingany
Note (i):)
applicable by ticks in the
left hand
boxes
applicable.
the appropriate
details when the Sections for
Person
should
tick each applicable righthand
The Authorised
Note (iv):) This Sanction-to-Test
contains6 sections.)
Note
to Work
16.2.1
ANNEX
Note
Permits
1 COSWP
Appendix
box
(Hi):
as
they
Other
Work
make their check.
SECTION A - Scope of Work)
Location
.......................................................................................................................)
of space)
(designation
Plant Apparatus/Identification
(d esig
nation
Work
to
of ma ch i ne ry / eq u i p me nt)
be done
Permitissuedto
(description)
of
(name
............
. ........
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .)
..........................................................................................................................)
person
carrying
out work or in
charge
of the
work party)
system
at the
......................................)
Data)
Section B - CheckList/Isolation
Has
a risk
(Description)
Circuit
(These
of the proposed work been carried out?
is
dead and has beenisolatedfrom the
apparatus
assessment
The above
Earths
have been applied to the equipment
at
the
Earths may be removedand replacedto your
instructions)
Main
(Description)
location
following
..............................................................................................................................
Safety Locks
(Detail
following points
.... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .)
fitted
and
points.
........................)
identify lock set) ...................................................................................................
182
Electrical
Marine
Practical
to avoid danger have
Precautions
Additional
Knowledge)
taken
been
by
...........................................................................................................................
(Descri ptio n) ....................... ...
have
notices
Caution/Danger
.)
been applied at all
and Safety Signs appropriately
of isolation,
points
positioned.)
C
SECTION
Periodof
-
AND AREAS AS DANGEROUS)
APPARATUS
OTHER
ALL
TREAT
of Sanction-to-Test)
Authorisin9
...........
sanction-to-test
of
validity
above equipment is dead and
isolated
I hereby
not exceed 24 hours)
hours.
(should
all live conductors and connected to earth.
.
(Name).....................................................................
D
SECTION
I accept
................................................................
(Date)......
for carrying
satisfied
of
the
out the work on the apparatus detailedon this sanction-to-test
and no
to work on any other apparatus or in any other
area.
charge
will be maintained for the
have been taken and that safety
arrangements
by me or people under my
will
duration
that all precautions
work.)
Key No........................................................
Safety
.)
of Sanction-to-Test)
Receipt
responsibility
be made
attempt
I am
-
...............................................................
(Signature)
.......................................................................)
me)
that the
person)
Authorising
(Ti
declare
from
Received*/Applied*)
Competentperson
. (S n atu re ) ...............................................................
(Name)....................................................................
ig
(Ti
......................................................................)
me)
Note:
After
signing
where the work
The work
for
which
have
been
permit
to work.
work
equipment,
Competent
me)
Safety
at the
place
of Sanction-to-Test)
this sanction-to-test
was issued is now suspended*/completed*
and all people under my
withdrawn and warned that it is no longer safe to work on the apparatus detailed in this
tools,
test instruments
etc have
removed.
been
person)
(Name).................................................................... .
(Ti
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .)
the receipt, this sanction-to-test should be retained
in charge
by the person
carried out until work
is complete
and the clearance section signed)
- Clearance
charge
All
ate).
is being
E
SECTION
(D
.
(Signature)..............................................................
......................................................................
(D
Key No........................................................)
Received*
ate).
......................................................................
/ Applied*)))
1 COSWP
Appendix
Permits
to Work
183)
Test)
SECTION F - Cancellation of Sanction-to-
This
Sanction-to-Test
Authorising
(N
is cancelled.
Person
a me ). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
(Ti me)
.......................................................................
(S
i9 n
....... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
atu re ) ..
.
(Date)......................................................................
Received*
Safety Key No.........................................................)
* Delete words not
and where
applicable
appropriate state:
The work is complete*/incomplete*
asfollows:
(description))
.
/ Applied*)
..............................................................................................................................
..............................................)
..............................................................................................................................
..............................................)
..............................................................................................................................
.............................................
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Index)
Electric Propulsion
A
Alarm
141
Apparatus
Gas
Automatic
Diagrams
Electrical
Maintenance
120, 123
Regulation
(AVR)
Electrical Safety 7
Voltage
Groups
57-60
82-84
Starter
Autotransformer
145-146)
Azipod Thruster
3-6
Electrical
113-115
Monitoring
Alkaline Battery
15-17
132
Electrical
Survey
Electrical
Testing
EmergencyGenerator
and
Types
Battery
112, 137-138
112-116
Maintenance
and
Supplies
Battery
Charging
Bearings 99
Busbar
and
44-48
Testing
Capacitor-startMotors
Breakers
Circuit
Breakers
2-3
Condition
131
Monitoring
GeneratorOperation
Generator
16-17
Generatorsand
Inversion
and
Rectification
163)
D
14
Direct-on-Line
(DOL)
Filter
90, 163, 166
Harmonics 89-90, 150-151,161-163
Harmonic
135
Diode Tests
132
Survey
144)
60-64,
H
Current Injection Testing
41, 135
Current Transformer (CT) 26, 32, 40-41,
156-157,
Governors
Parallel
in
, 49-52
65-66
151-152
14-15
Cycloconverter
66-67
20-21
Protection
Generators
55-57
Methods
Maintenance
57-58
12
Clampmeter
52-55
55
Cooling
Generator
Converter Types 152-157
Current
20
Construction
Generator
97
Motors
Controlled
42)
GeneratorExcitation
Excitation
Continuity Testing
FuseProtection
Flameproof Enclosure 119-123
Generator
36-44
Societies
Commutator
118-119
Gas Groups 120,123
10-15
Testing
17
Finding
Fire Triangle
Galley Equipment
23-28
Faults
Classification
128-129
142
G
170
Circuit Protection
Compound
134-135, 166
4-6
Circuit Earthing
Circuit
37-39, 68-71,
134-135
Survey
Diagrams
Circuit
Maintenance
Apparatus
Fault
109-110
28-29,
Circuit Calculations
Circuit
137-138
EmergencySupplies 21-22
F
96
Protection
Circuit
Power Survey
Ex Temperature
135-136
Cables Survey
Cathodic
Emergency
102,
Class 119-121
Explosion Protection 117, 121-122)
170)
Earthing
C
CableTypes
Lighting
Ex Certification
66
49, 64
104-105
21,
Emergency
Ex
BrushlessGenerator
128
Areas
Hazardous
in
163
EMC
B
158-160
Operation
System
7-8, 168-169
Electric Shock
107 -108
Air Conditioning
Starter
Distribution Circuit
Breakers
Distribution System
19-22)
Area
Electrical
Hazardous Area
Equipment
Hazardous
Hazardous
Zones
HV
Circuit
Breakers
HV
Insulation
Testing
128
126-128
117
166
167
80
HV on Ships
166
28-29
HV
Protection
Scheme
HV
Safety
36
168-169
HV Testing
171-173)
E
Earth
Faults
24-28
Earthed Neutral
Earthing Down
I
System
22
IGBT
169-171
Electric Cables 44-48
Electric
Propulsion
Electric Propulsion
Auxiliaries
Options
163
145)
88, 154
Impressed
Current
I ncreased
Safety
Induction
Motor
Maintenance
Induction
Motor
Protection
Cathodic
Exe
Protection
125-126
97 -100
90-96)))
109-112
Marine Electrical
Practical
186
Induction
Motor
Induction
Motor
Speed
Control
Starting
80-85
Protective Discrimination
36,
Pulse-mode Operation 159
Ingress Protection (IP Code) 73
Transformers
Instrument
Insulated
Neutral System
Insulation
Class
Insulation
Resistance
Insulation
Resistance
R
Rectification
19
ReducedVoltage
Refrigeration
8-11
163
123-125
Lead-acid Battery
112-113
between
Generators
Location
Lighting
(LLL)
Motor
Enclosures
Motor
Operation
96
5-6, 81-82, 85
138-139
135
Survey
Synchroconverter 150, 152,155,158,161
97-100
73, 75, 76
Ratings
148-151
76-78,
60-63
of Generators
Synchronising
90-96
85-90
Control
Synchronous
T
Tanker Survey
Motor
155, 158)
149-150,
Operation
Testing in Hazardous
THO 161-162
137
10,12-14)
88,
Thyristor
Navigation
and
Lights
Non-sparking
Signal Lights 101-103
139-140
Survey
Exn
122,
126)
91
128
Areas
152
164-165
Cooling and Protection
Harmonic
Distortion
Transformers
29-31)
Total
Navigation
141-142
(Electrical)
Sensors
Temperature
N
161-162
U
UMS
140-141
Survey
Operation
Undervoltage Protection 36-37,42-44,95
o
Overcurrent Protection (OCR)
4, 39-42,82, 91-95,166)
UPSSystems
115-116)
104,
V
p
Parallel
Operation
to Work
of Generators 60-64, 144
168-170, 175-183
PI (Polarisation Index)
172
16
Maintenance
Planned
Power Distribution System
Factor
3,51-52
PreferenceTripping
Pressurised
Types
Exp
19-21,160
146-148
(VTs)
126-127
and Operation
90-96, 165-166)
68-69,
88-89
32
88-90, 150,154)
W
Ward-Leonard
Wiring
Protection of Generators 65-66
of Motors
Transformers
VSD (Motor Control)
20-21
Enclosure
Motor
Vacuum and SF6 Interrupters
Variable Frequency Control
57 -60
Regulation
Voltage
Voltage
19-21
Power Management System (PMS)
Power
for Electric Propulsion
Supply
Protection
141
SteeringGearSurvey
Thyristor
Propulsion
Detection
and
Multimeters
Power
90, 94-95
Starter
Switchboards
Motor Starting
44, 81-85
Motors and Starters Survey
Permit
96-97
Protection
Fire
Star-Delta
73-74
Motor Protection
Speed
33-36
Types
Split-phaseMotor
Maintenance
Braking
Motor
Motor
68-71
160
Motor Construction
Motor
of Motors
84-85
Soft Starting
SOLAS Regulations
21, 131
28-29
Starter
and
Operation
Connection
Single Phase
Single-phasing
Smokeand
172
Micro-ohmmeter
Motor
104)
67-68, 135
MCBs
and
MCCBs
59, 60, 63-64, 132
19-21
Main Switchboard
Generator
ShoreSupply
LoadSharing
M
Main Circuit Breakers
96-97
51-52
143-146
Scheme
Ship ElectricPropulsion
1-6
Electrical
Ships
System
15, 169
Testers
7, 108, 123-127, 168-170
Safety
Shaded-poleMotor
151-152)
Supply
43-44, 66, 135)
S
L
Main
87
Power Protection
Reverse
Shaft
Low
79,81-85
105-108
10
(Noise)
Live-line
Starting
Equipment
RegenerativeBraking
137
Survey
Intrinsic Safety Exi
Inversion
151-153
32
9
Insulation Testing
I nterference
65
154)
Converter
PWM
38-39,
172 -173
Testing
Image
86-90
73-74, 76-79,96-97
Induction Motors
Infrared
Knowledge)
Speed
4-7,
Diagrams
Wound-rotor Motor
67
Control
148-150
Z
Zener Barrier
87-88
Control
124-125, 142)))
87)
166,
173
\"\"')
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INTERNATIONAL)
Witherby
Seamanship
4 Dunlop
Square,
Edinburgh,
International
Livingston
EH54 8SB
Scotland,UK
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No: +44(0)1506
468999)
Tel No:
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ISBN: 978-1-85609-623-2)
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