Ll$RARY
ROYAL AIRCRAFT ESTABLISHMENT
C.P.
No.
1 I86
BEDFORD.
.
z
PROCUREMENT
EXECUTIVE, MINISTRY OF DEFENCE
AERONAUTICAL
RESEARCH
CURRENT
COUNCIL,
PAPERS
A Feasibility Study on a 200 Volt,
Direct Current,
Aircraft
Electrical Power System
The Staff of the Aux~llary Power Systems DIVISIOII
of Engrneering Physrcs Deportment
LONDON:
HER MAJESTY’S STATIONERY OFFICE
1971
PRICE 90p NET
U.D.C.
629.13.066
: 629.13.072
LIBRARY
R3YAL AIRCRAFT ESTABLISH~+!f
EEDFORB.
A FEASIBILITY
STUDY ON A 200 VOLT,
AIRCRAFT
ELECTRICAL
CP No.
January
1186*>k
1970
DIRECT CURRENT,
POWER SYSTEM
by
The Staff
of
the
Auxiliary
of Engineering
For
comparative
commercial
purposes,
aircraft
has been
conventional
three-phase
studies
been
have
Interruption,
the
has also
not
the
due to
been
It
in
conversion
system
is
of
be lighter
is
combat
of
for
weight
with
the
motors.
arcs
modern
design
dc generator,
sustained
a large
compared
necessary
and brushless
also
that
the
considerable
equipment
that
of
a
informatlon,
problem
of
circuit
The vulnerability
during
fault
of
conditions
weight
and brushless
reducuon
motors,
can be achieved
the
dc system
will
ac system.
concluded
dc arcing
until
at
that
the
altitude
200 volt
especially
dc system
in
would
a military
be vulnerable
aircraft
subject
damage.
Departmental
*
and Its
a 50 kW brushless
possibility
conversion
than
catastrophic
dc system
To obtain
equipment
Dlvlslon
Department*
a 200 volt
designed
Systems
examned.
concluded
design
It
the
Physics
ac system.
made of
Power
Reference:
EP 543
The work was dlrected
by Dr. C. S. Hudson when in Instruments
and
l.e.,
before
the Aunliary
Power
Electrical
Engineering
Department,
Many of the Staff
concerned
in the study
Systems i)lvislon
was formed.
are now members
of this
new Division
of Enguwering
Physics
Department.
**
Replaces
RAE Technical
Report
70012
- ARC 32640.
to
to
CONTENTS
P*
INTRODUCTION
THE PROGRAMME
OF WORK
GENERALDISC'JSSION ON THE TECHNICAL ASPECTS OF THE
200 VOLT DC SYSTEM
3.1 Generatron
3.2 System control and protection
3.3 Switchgear
Power conversion
3.5 Weight comparisons
3.6
Arcng
CONCLUSIONS
Appendn A Description
of the systems considered
comparison
3
4
5
5
7
7
9
11
3.4
Appendn
Appendix
Appendix
Appendix
S
C
D
E
13
14
in the weight
15
Factors influencing
the design of the generator
Proposals for system control and protection
Survey of methods of switching for 200 volt dc systems
Types of power convertor proposed for motors and
secondary dc supplxs
Appendix F Weight comparison between 200 volt
Appendix G Arcing tests
Tables 1-7
References
111ustrat10n.5
Detachable abstract cards
17
21
24
28
ac and dc systems
31
34
35-41
42
Figures
1-4.
3
INTRODUCTION
1
The present
the
200 volt
In
this
of
the
electrIca
power
400 Hz three-phase
system
the
alrcraft
are
constant
and parallel
running
in
of
generator
years
installed
lncreaslngly
concerned
dlstributlon
system,
craft.
of
dlminlshing
electrical
system
to reduce
the
operating
voltage,
posslbillty
of
examined
of
this
weight
increaslng
in
the
Conslderlng
case
the
an operating
operating
effectively
to be deslgned
very
with
peak
voltage
a peak
voltage
to peak
earth
system
utilization
factor
of
appreciably
lighter
than
A dc system
but
operating
was abandoned
generators
used.
made in
semi-conductor
problems
in
the
of
days
However,
power
of
the
At a joint
Society
Colloquium
by an R.A.E.
paper
the
due to
in
the
devices.
generation
112 volt
1966
entitled
has been
with
an earthed
at
little
least
to neutral,
but
This
a single
200 volts,
and
giving
a dc System
three-phase
the
1:5.
440 volts,
that
has
Hence,
having
be made
be about
the
a
should
be
ac system.
in
Valiant
and Vulcan
by commutator,flashover
years
rapid
made possible
that
is
approximately
a dc system
neutral,
cable
580 volts.
i.e.
appear
advantage
cable.
each
rms
could
would
have
The
wue
would
and conversion
could
not
of
advances
the
I
the
have
solutions
have
been
been
of
solved
system.
Institution
in
used.
three
twenty
These
the
is
was used
last
system
overall
can be done
of
voltage
failure
Little
runs
by using
112volts
the
long
corresponding
at
of
1s now
very
115:5X&
it
weight
air-
and
this
to 400 volts
115 volts
and
the
with
1s only
Hence
of
but
line-to-line,
become
generator
show
of
growth
have
increasIng
of
e.g.
voltage
has to withstand
1:2.2.
type
engines
rapid
to
only
operating
the
war.
automatic
drive,
weight,
either,
the
rms
However,
the
return,
the
aircraft,
of
main
found
system
200 volts
the
weight
system.
voltage
1939-44
the
generator,
of
by,
in
alrcraft
to withstand
figure.
the
bulk
and has been
of
empty
to reduce
the
the
made for
power
the
to
1s
constructors
of
than
operating
present
is
electrical
given
other
at a voltage
utilisation
wire
the
the
change
large
voltage
effective
a poor
system
from
With
and distribution
occasions
second,
and for
of
of
speed
provIsion
3-7Z
HOWeVer,
the
of
of
alrcraft
after
generators.
equipment
supply
modern
capacity,aircraft
or a fundamental
on a number
except
ratio
the
constant
the
has been
returns.
1s in
of
weight
and protection
most
soon
drives,and
at about
attention
control
an area
the
now running
Considerable
assocuted
is
about
at
speed
in
introduced
driven
synchronlsatlon
recent
in use
ac system
generators
through
system
of
the
Electrical
topic
of
“A preliminary
Engineers
dc systems
survey
and Royal
for
of
aircraft
a 7.00 volt
Aeronautical
was introduced
dc system
for
4
aircraft".
This
Aircraft
Establishment,
electrical
paper
system
aircraft
should
The system
network,
further
should
have
built
to
form
required
the
Following
object
of
system.
This
work
with
pole
into
them
lightweight
by the
equipment.
a programme
could
interface
of
was to examine
which
further
in
units
work
more
completed
the
and is
large
require-
either
It
engine.
use dc power
the
was approved.
technlcal
summarised
this
dc
The
aspects
in
was
directly
converting
by R.A.E.
detail
aircraft
distribution
the
for
Royal
for
engine,
of
not
main
power
the
part
the
system
return
from
at
the
limited
earth
directly
loads
dc for
a 200 volt
as an integral
and
done
of
the
Report.
THE PROGRAMME OF WORK
2
To enable
an assessment
two equivalent
having
systems,
The weight
ac system.
a generator
For
practice.
this
was chosen
compared
are
cussed
in
In
was
designed
or
that
the
machine.
serious
commutation
Appendix
of
of
weight
for
the
the
for
control
of areas
the
was needed
These
of
pre-production
future
Concorde
The systems
given
of work
three-phase
an aircraft
and protection
are
weights
as possible
comparison.
comparisons
made.
would
with
subtransient
be a wide
a polyphase
of
the
needed
in
were
before
dis-
F.
in which
a dc system
the
is
Appendix
defined
comprise
ripple.
rev/min
This,
speed
bridge
switching
reactance
a reasonable
12000-24000
B.
information
Because
the
range
design
needed
alternator
to obtain
a number
a conventIona
be made
of
the
could
it
be
following:
design
to keep
and
A,
weight
other
system
basis
this,
an estimate
The generator
brushless
the
to compare
as representative
generating
in Appendix
the
naturally
configuration
the
was decided
dc and
should
as a suitable
to
Generator
(a)
load
C, and
addition
considered
one being
reason
described
Appendix
to be made it
comparison
and
aircraft
of
driven
work
use of
aircraft
a single
or built-in
has now been
the
proposing
comprised
equipment
work
that
small
that
this,
this
for
dc generators
present
suggested
some preliminary
be reconsidered,
envisaged
as at
of
suggested
28 volts
and brushless
externally
result
and it
and retaining
ments.
of
was the
of
rectifier
action
the
machine
however,
assessment
has been
range
of
dc machine
comprising
built
the
the
rectifier
as low
increases
into
the
it
of weight,
a machine
operating
designed.
This
is
work
is
as possible
weight
of
end
a
frame
necessary
to avoid
the
described
machine
over
a speed
in
5
-SW1tching /I
(b)
Work done
tion
with,the
cated
112 volt
that
200 volt
there
dc,
been
done
work
is
described
the
in
are
used
load
The modern
an-&iduction
C
the
motor
Work
tin
at
at high
altitudes.
methods
of
Appendix
D.
for
fuel
motor
of
in
connec-
I aircraft
circuit
interruption
indi-
interruption
wxth
work
has
been
examined.
have
is
for
the
supplied
from
the
200 volt
wave
therefore
This
equipments
the
will
need
studies
in
suitable
of
power.
ac systems
1s a simple
A brushless
dc motor
appears
to be the
dc supply
through
that
motor
the
the
etc.,
loss
use of
a square
would
of
wave
run
satis-
performance
motor-inverter
unit
and
compared
with
.
a built
it
use
appreciable
weight
motor.
dc and converts
Design
without
equipment,
installed
purpose.
to e'stablish
s‘upply
to assess
most
conditioning
the
in
the
but
a square
of
motor
ideal
Lo be done
air
part
ways
ac induction
200 volt
driving
ac induction
to the
needed
compired
tith
the transformer
I _
This work is described
in
'interface'
various
unit
levels
of power
to be made to assess
rectifier
units
in Appendix
which
the
receives
required
weight
at present
used
in
of
arcing
of
power
in
the
such
units
equlpments.
E.
Vulnerability
Cd)
A cause
for
concern
was the
dc sysiem if a fault
occurred,
.,
p&pas
by Foust and Hutton12,and
some"increase
Their
in
tests,
arcing
however,
therefore
been
Appendix
G and
3.1
R.A.E.
and Vulcan
Some further
circuit
pumping,
which
needed
equivalent
equipment.
3
Valiant
problem
various
and also
Most
.
serious
three-phase
robust
-:
may be achieved
in
efficiency
the
may be an appreciable
lig'htweight
factorily
in
the
conversion
total
lnverter.
used
at
and Gi111'2y3
be a fairly
particularly
Motors
and
ago by Mossop
dc system
would
and various
Power
Cc)
some years
time
were
made at
in
The design
no new fundamental
particularly
limited
altitudes
problems.
at
circuit
altitude
with
high
altitudes.
up to 60000
ft.
These
damage
with
to the airframe.
13 indicated
that
and Davidson
to moderate
voltage
Further
are
described
dc.
tests
have
in
repor&.
ON THE TECHNICAL
and manufacture
greater
a short
by Cunningham
was likely
a separate
GENERAL DISCUSSION
I. I
Generation,
possibility
of
ASPECTS OF THE 200 VOLT DC SYSTEM
a brushless
The generator
would
200 volt
consist
dc generator
of
present
a three-phase,
a
6
rotating-diode,
brushless
rectifier
to produce
be mounted
could
rn
be air,
alternator,
the
case
or,
preferably,
for
excitation
power.
A filter
acceptable
level;
it
The basic
respect
range
of
200% for
ripple
filter
more
say
be called
for,
with
The manner
generator
to
is
power
and a speed
to power
if
8000
rev/min,
weight
of
of
oil
range
it
equal.
This
rotor.
The
is
is
rated
operation
440 volt
before
The overall
the
rectifier
in
the
most
effectively
for
the
subtransient
at
could
it
being
is
top
thought
reduced
weight
and filter
of
that
is
for
for
the
is
required,
gives
the
P
a weight
alternator
conventional
In
weight
order
‘2
400 HZ,
to minimise
the
is
feeding
to
reduce
In
order
should
far
of
voltage
therefore
be made
a damper
small
a variable-speed
of
of
2:l.
range
could
in
on the
machine
of full
surge
a
and
winding
and on removal
a speed
estimated
speeds
This
voltage
a 50 kW oil-cooled
units,
to minimise
the
alternator
surges
by voltage-regulator
of
the
by means
the
design
Since
mode.
from
might
and
an initial
be expected
cooling
required,
machine,
speed
to no
is
inductances
voltage
The
frequency
proposed.
achieved
and
165OC.
the
lb/kVA).
switched
a constant-speed
running
(1.5
alternator
Hz is
switching
voltage
abnormal
power
than
a speed
seconds.
oil
proposed.
less
over
voltage
aircraft
that
A
5 minutes
ripple
speed
an
the
diodes.
1.5
at high
minimum
are
power
300% for
shown
to
reliability,
for
affect
is
the
rated
up to about
operation
appreciably
2400
operating
is
rev/rain
a high
to
It
at
similar
loss
than
a machine
is
of
1200
24000
lb/kVA
which
transient
to be higher
of
1.2
filter
of
commutation
twice
about
ripple
B.
and
voltage
rectifier
full-load
of
itself
to
of
requirements
Appendix
12000
machines
the
basic
high
current
1n advanced
alternator
cooled,
a rectifier
from
of
of
currents
the
ripple
application
output
150% full-load
temperatures
the
in
the
range
alone,
the
of
ratio
frequency
in which
the
control
case.
with
delivery
to reduce
inlet
discussed
ratio
the
peak-to-peak.
oil
this
This
liquid.
supply
alternator
coupled
and
to
the
would
coolant.
a suitable
for
ratio,
of
the
diodes
alternator
reduce
generator
for
be required
20 volts,
to
in
bearings
call
rectifier
be incorporated,
and short-circuit
would
than
the
currents
5 seconds,
aircraft,
be mounted
the
would
overload
2:1,
high-speed
to power
of
specification
by the
be fitted
of
a low weight
in
typical
would
full-wave,
The output
and cooled
would
would
requirements
of
particularly
exciter
too
a silicon-diode,
dc output.
alternator
pilot
attainment
required
the
A permanent-magnet
feeding
fact
the
tend
load
order
of
Under
rise
to
about
the
weight
actibn.
generator,
including
to be 105 lb,
compared
with
a
7
weight
3
of
real-power
engine
i
about
output.
drive
the
there
System
would
control
to
C and
achieve
and
instant
generator
and
generator-cable
the
voltage
fault
estimated
amblent
air
a positive
means
the
5
nor
simpler
than
problem
is
that
of
voltage-control
frequency
solution
at
the
regard
by
protection
an ac
circuits
3.3
at
and
in
of
operate
varies.
This
in
are
irrelevant,
will
tend
using
gain
round
to
improve
met
generators,
subnormal.
the
is
The
with
and
voltage
reliability
protection
control
and
much
simpler
is
I
capable
under-frequency
the
diodes
variable-
regulator6.
under-voltage
therefore
generator
in
is
much
only
the
over-frequency,
main-line
example
operation
is
provide
frequency
of
while
On balance
dc system
neither
used.
in
do not
is
are
complexity
natural
for
voltage
needs
weight,
in
with
diodes
dc brushless
and
busbars,
problem
a dc system,
diodes.
ft,
so parallel
variations
size
diodes
generated
the
over-
operating
main-line
main-line
some added
protection
the
also
simplify
of
the
faults,
They
in
70000
from
circuits,
28 volt
is
give
from
under-voltage
capable
that
1s shown
They
loads
and
up to
is
diodes
conditions.
a dc system
when
speed
expense
This
the
in
circuitry.
circuits,
generators
sharing
main-line
disadvantage
up and
for
of
fault
altitudes
problems,
as the
such
problem
especially
a parallel
to
same
ac,
discussed
generator
a 50 kW unit
run
are
and consumers’
and
main
the
being
main-line
system.
to
70°C,
protection
the
of
for
compensating
to
and phase-sequence
achieved
16 lb
control
alternators
With
for
is
loop
the
coupled
generating
system-control
protection
A minor
ac,
of
some 64 lb.
protection
faults
Their
reactive-load
with
of
busbars
under
of disconnecting
to
when
The use
the
earth
up to
regard
regulators
of
under-voltage
engine
and
in
supply
cooling.
first
With
of
for
temperatures
convective
when
Isolation
discrimination.
3
1500 XI
and
at
control
elsewhere5.
a ‘no-break’
need
alternator
be directly
essential
saving
simplifications
and
obviate
would
unit,
weight
400 Hz,
protection
detail
of
60 kVA,
generator
speed
system
more
a number
providing
the
be a net
automatic
thus
.
since
for
in
a conventional
constant
The proposals
Appendix
for
But
and
eliminated
3.2
90 lb
since
there
iS
than
are
fewer
inadvertently.
Switchgear
In
the
existing
dc,
or
the
115/200
environment
types
volts
of
experienced
aircraft
ac systems,
in
modern
switchgear,
will
function
high
designed
altitude
for
satisfactorily
aircraft,
28 volts
dc,
at
none
of
112 volts
200 volts
dc.
8
The ac switchgear relies upon the periodic zeros and reversals of the current
to extinguish
the arc very soon after it has been drawn. DC supplies provide
dc switchno natural zeros or reversals of the current, so purely-mechanical
gear has to be specially
designed to build up an arc voltage drop greater than
the supply can maintain.
The difficulty
of dc switching therefore increases
Because of these factors an investigation
of many possible
with the voltage.
methods of switching 200 volts dc power, over a wide range of currents, was
These studies
undertaken in order to find which would be the most suitable.
are briefly
described in Appendix D and are fully reported on elsewhere 7,899 .
The following
is a brief summary of the findings.
Conventional aircraft
switchgear is purely mechanical in operation.
That used in 112 volts dc systems was unsealed, and achieved current interruption by using multiple
gaps or deion grids to produce a number of arcs =n series.
The same techniques are proposed for 200 volts dc, though even for low rated
currents a multiple-gap
switch would require eight short series gaps. This
would demand careful manufacture to achieve virtually
simultaneous opening of
the gaps in order to minimise the arcing times amd maximise the endurance.
For
high rated currents and for rupturing fault currents deion grids, used in
conjunction with four long gaps, are the proposed solution.
With either type
however it might prove difficult
to achieve the sort of contact endurance
figures currently
provided by modern aircraft
switchgear (50000 operations).
A sealed contact enclosure with oil or compressed air or nitrogen might provide
a lighter
and more durable switch than the unsealed air-break types, at the
expense of considerable development work to prove seal integrity
and contact
endurance.
The application
of forced-commutation
techniques to ac-type mechanical
switchgear and to thyristors
to achieve dc switching is quite feasible,
though
the technique has several disadvantages.
A large and heavy cormnutation
capacitor is required,
the size of which is related to the maximum overload
capacity of the switch, and short-circuit
fault currents cannot-be ruptured.
*In the thyristor
switch, the commutation circuit
imposes an overvoltage across
the load during switch-off,
whilst a large heat sink is necessary to dissipate
the heat generated in the thyristor.
The heat generation and t:le heat sink can
be eliminated by the connection of mechanical back-up contacts across the
thyristor,
resulting
in a large weight reduction,
but the operational
disadvantages of forced commutation remain. These include the possibility
of the
thyristor
contacts.
failing
to conduct,
when it
would be unsafe to open the back up
9
Estimates
two
representative
for
ac switchgear
mechanical
than
ratings
of
type
any other
least
is
of
sort
more
Power
of
all
the
would
Flying-control
(c)
Navigational
(d)
Communication
(e)
Power
equipment,
Appendix
E.
must
invertor
on starting,
the
heavier
than
further
alternating
equivalent
contact
interruption
endurance,
weight
increase.
direct
current
of
current.
current
and
of
the
varies
with
the
weight
cool
of,
dc supply
input-power
would
convertors
The major
of
fuel
enough
of
supply
types
in
of
equipment
more
motors
(a).
fed
by a relatively
continuous-running
the
maximum
motor
current,
the
associated
of
and voltage
at
employed.
For
an invertor
is
expense
very
ambient
in
the
of an induction
manner
motor
some weight
as a heat
sink
designed
reduction
the
of
Fig.3.
to run
would
thyristors.
at
is
circuit
the
70°C at
and
It
occurs
reduces
upon
cooling
in
it
both
much dependent
shown
for
normally
increased
forced-air
in
The use of
invertor
temperatures
employing
detail
duties.
This
of
the
unsophisticated,
which
at starting.
the
supply
in
for
weight
to
discussed
proposed
invertor
to act
proposed
is
the
pump motors
dc system
electric
motor
torque,
kVA rating
are
two are
to
the
the
28 volts
convertor
first
frequency
cooling
weight
for
reduce
the
the
induction
increases
the
of
power
invertor
The weight
and quality
by a 200 volts
equipment.
supply
invertors
so to
to reduce
were
of
be rated
and
complexity.
fuel
to
of which
The
case
and cheaper
equipment
types
thyristor
the
smaller
equipment
convertors
square-wave,
In
and/or
estimates
The purely
a comparable
redesign
consuming
ac squirrel-cage
times
capacity.
effort
of
with
for
equipment
Square-wave
(9
1.6
have
dc switch
motors
three
affected
control
together
lighter,
since
or the
existing
(b)
altitudes
1,
of
be:-
The following
the
not
that
types
some 50-100%
400 Hz ac supply
of,
Electric
proposed
is
inevitable,
than
the
(a)
robust
times
so it
might
Table
handling
development
are
introduction
practically
the
it
various
conversion
the
affected
in
several
even
difficult
Replacement
involve
is
but
for
summarised
considerable
this
and cost
same real-power
Furthermore
inherently
3.4
the
dc type,
without
Penalties
are
of dc switch
ac switchgear.
at
volume
of weight,
is
10000
type
low
frequency
about
rev/min.
be possible
if
the
10
(il)
in
each
the
DC transformers.
item
of
28 volts
and,
practicable
unit
penalty
at
not
the
would
system.
are
the
to use
frequency
voltage
which
(ill)
Cc) and
some
would
be required
3-5
normally
obtain
system.
For
in
it
straight
require
systems,
penalty
from
would
Reliability
and
practically
equipment
every
arise
could
dc aircraft
unable
to increase
it
a lower
turn-off
would
then
operating
reasonable-quality
consuming
as shown
use power
from
invertors
equipment
sine-wave
the
in
by changing
by the
the
Fig.3.
They
ac form
and
400 Hz ac power
ac power
fed
invertors
in
primary
precision-quality
junction
sensitivity
to
fans,
drives
severe.
cost
of power
item
of
invertor
can hardly
maximum
invertor
which
these
and fast
being
requirements,
transformation
which
rating
electronic
finally
by
they
200 volts
generate
those
equipments
dc supply,
require
lnvertors,
or variable-frequency
cooling
exact
most
penalty.
to
ln
be a weight
in
thyristors
would
needed
would
and obtain
28 volts
primary
it,
dc system,
power
system
to
dc.
With
more
in
the
in
voltage
weight
levels
the
at
fast-turn-off
found
a practical
fast-turn-off
This
voltage
of
considered
manufacturers
a greater
upon
there
thyristors
in
the
their
are
weight
invertor
modern
ratings
as much as square-wave
equipments
3.4.1
the
times
weight
200 volts
in
with
a
the
the
although
of high
of
of
lnvertors
400 Hz ac power
no further
fixed-
result
Depending
Cd).
expected
thyristors.
at various
weigh
even
rating
Sine-wave
400 Hz ac power
the
requirements
slower
would
feasible
on a 200 volts
event
supply
The dc
to minimise
smaller
satisfactorily
the
to
a transformer,
order
same,
While
surges
and
and a 400 Hz transformer/rectifier
rather
packs.
Cd),
levels
transformers'.
to operate
is
the
power
and in
be necessary
3 kHz
'dc
voltage
and
invertor,
desirable
the
for
the
the
is
(c)
use
In
about
dc unit
Unfortunately
sufficiently
(b),
weigh
switching
IncompatIble,
to
a dc transformer
function
withstand
it
at various
(b),
thyristor
and
basis
electronic-equipment
estxnates
filter
1 kW would
against
proposed
a filter.
frequency,
On this
rated
is
necessary,
and the
thyristors.
it
dc power
equipment
a square-wave
where
transformer
highest
consuming
(e),
compr~es
rectifier
the
electronic
dc system
transformer
To generate
fail
ambient
which,
if
except
run
consuming
to
feed
to be worsened.
temperature
the
convertors
permitted
air
in
temperature
for
continuously.
motor
it,
the
containin;
reliability
Furthermore,
thyristors
would
interference
a built-in
and cost
the
implies
and pressure
invertors,
Radio
equipment
rather
of
low
a greater
and a greater
themselves
problems
use
of
require
would
also
be
11
The only
mitigating
feature
voltage
regulation
into
acting
the
quality
of
consuming
their
3.4.2
due
The magnitude
forces
the
designer
weight
and
complexity
system
voltage
least
in
the
3.5
Weight
An
and
in
of
form,
consumer
as far
consumer
the
Since
protect
than
(e)
failures
expected
in
These
necessary
does
not
nor
the
in
to
improve
in
the
the
10
invertors
require
the
, and
addItiona
A reduction
in
the
transistors
to
be used,
with
it
power,
the
nominal
at
the
engine
of
the
the
effect
of
and whether
any
items
electrical
power
and
forming
two
to
supply
may be eliminated
operate
such
necessary
new power
switchgear,
to
items
between
course
power,
devices,
accessories
a comparison
is
equipment
of
electrical
include
it
the
protective
include
maklng
all
transmission
distribute
normally
in
comprises
and
to
does
electrical
system
drives
differences
ac,
greater
In
order
supply
affecting
can be run
of
the
dc
some saving
be distributed
the
dc switchgear
difficulty
to
avoid
motors
them.
in
as
basically
take
into
on the
or
part
weight
have
to
be
of
wires
will
without
system
is
simpler
should
a single
of
close
speed
control,
can be eliminated.
in
extinguishing
be brushless,
and
easier
to
control
be obtained.
,
wire
using
a three-phase
unreliability
must
weight
parallel
weight
with
three
in
ac system
a parallel-running
200 volts
to
normally
together
However
replacing
continuously-running
invertors
surges
enable
storage
etc.
as possible,
DC can
thus
inherently
of
speed
(b)
(d)
dc would
system’
As dc generators
(c)
of
(iii)
installation.
constant
return,
circuitry.
busbars;
It
Power
(a)
risk
transistors
connnutatlon
generatIon,
the
equipment
3.5.1
and
the
drives.
account,
to
of
instead.
equipment,
speed
added
and
ratings.
cabling,
forms
the
in
up to
different
of
(ii)
fast-
spikes.
voltage
use
50 volts
power
equi pment.
constant
the
and
thyristors
electrical
units,
the
about
used
consumer
reduce
surges
the
use
of
‘aircraft
control
thereby
types
incorporating
comparisons
cabling
any
of
of
load-switching
precludes
lower
possibility
invertors
voltage
the
to
to
the
transistors
of
dc system
and
to
The use of
200 volts
the
output,
equipment
is
general
earth
system
be heavier
(airframe)
with
one
because
wire.
of
the
dc arcs.
and rapid
brushwear,
thus
necessitating
all
200 volts
the
use
of
dc
12
form,
(f)
There
at
three-phase
adding
further
(g)
of
will
200 volt
invertors
cornplenty
A detailed
foregoing
layout
and
comparison
differences
between
Summary
are
in
shown
for
alternatlve
methods
in
in
is
are
of
aircraft
motor
turn
size
of
cable
in
possible.
assess
the
overall
and based
effect
on the
Concorde,
ac and dc primary
electrical
in
the
most
(b)
of
system
is
described
will
reduce
which
the
of
the
542
lb.
Both
of
in
the
size
the
of
a reduction
by a smaller
amount
saving
in
the
cable
where
of
is
driving
figures
and
weight
a weight
vary
dc system
circuit-breaker
However
is
protection,
these
two
figures
heavier
by 234
lb
or
to be produced.
the
invertors
quantity
and
would
and by the
or by 160 lb when
form
only
when both
fuses
3.1% and
where
from
be
elimination
C.S.Ds.
the
a
size).
requirement
C.S.Ds.
lb,
and
ac motors,
will
power
of
610
considerably
there
primary
weight
is
minimum
is
this
elimination
cables
than
for
but
on which
secondary-power
generators,
in
weight
ac cables
dc system
these
wherever
heavier,
and by the
greater
invertors
of manual
fuses,
three-phase,
power,
use of
the
cable
those
200 volts
secondary
reduce
the
are
are
in
200 volts,
any reduction
also
Thus
the
which
of
but
The saving
of
two
only.
cables
of
weight
7 considers
by means
dc items
weight
the
(A) by means
(A)
in
power
of
Table
(B)
sawngs
the
all
in
increase
the
gear.
provision
must
systems.
method
areas
cables
in
a breakdown
and
for
weight
(i.e.
and
used.
5 is
control
areas
load
offset
7 gives
of
to one half
the
lb,
On balance
manual
is
ac voltages.
protection:-
Table
possible
a weight
in
lighter
equipment
pre-production
ac and dc systems,
their
two
330
,This
partially
to
the
Table
parts
that
to aircraft,
the
means
comparison
5, while
single-phase,
(a)
is
both
equal
115 volts,
there
in
of utilisation-circuit
and
saving
increase
This
consumer
transforming
ac and dc systems
200 volt
by substantial
fact
There
the
systems.
offset
heavier:-
of
be seen
C.S.Ds.
those
in
both
will
1s almost
weight
sine-wave
and 26 volt.
within
for
undertaken
weight
individual
in
possible,
is
that
used
the
Table
the
circuit-breakers
which
of
weights
differences
the
dc voltages
than
weight
The total
It
transforming
equipment
115 volt
in
F.
3.5.2
systems
some 400 Hz ac power,
dc installation.
and weight
consuming
in Appendix
of
for
for
and single-phase
to the
Equipment
greater
the
be a requirement
systems
are
2.1% of
use
used
where
the
overall
of
13
electrical
installation
weight (7600 lb).
Very broadly, the weight penalty or
advantage of a 200 volts dc system will be governed by the following
two
principal
considerations:(a) the greater the length of cabling from the
generators to the busbars and to the major consumers the greater will be
the weight advantage;
(b) the greater the proportion
of motors and other
ac consumers the greater will be the weight penalty.
Concorde rates highly on
both points, and may therefore be said to be a fair choice of aircraft
for
making the comparison.
Thus, making due allowance for estimation'errors,
there
is unlikely
to be a large weight saving by using 200 volts
with the type of mixed load pattern cormnonat present.
3.6
dc in any aircraft
Arcing
Some tests were made to compare the maximum length of arc which could be
sustained by a 200 volts dc system with that for a 200 volts ac system, over
a range of altitudes4.
The arcs were struck between large brass electrodes in
a high-altitude
chamber by the fusing of strips of aluminium foil connected
between them. The power supply was 200 volts,
400 Hz, ac (line-to-line
connection),
or 200 volts dc, and the arc current was limited
by a series
resistance of about 1 ohm. The test procedure is described in Appendix G, and
the dc results are plotted in Fig.&.
This shows the maximum gap length across
which an arc could be sustained, as a function of altitude.
It will be seen
that at 60000 ft a dc arc could be sustained over a 7 inch gap, the arc
current and voltage being approximately
110 amperes and 90 volts.
If the
limiting
resistance were removed, to simulate an earth fault,
the arc current
In contrast,
with
would rise and the gap length could be further increased.
a 200 volts
down to l/16
ac supply it was not found possible
inch,
even at altitudes
to sustain
of up to SO000 ft.
an arc with
any gap
,
These tests indicate that in the event of an earth fault at high altitude
the damage that would be caused by the arc before extinguishing
itself
would
be vary much greater in the dc system than in the ac system.
Indeed the dc
arc might never extinguish
itself
if, for example, it occurred between a main
generator cable and an adjacent large structural
member, and the arc might
Of course the occurrence of a sustained arc
burn right back to the generator.
does depend upon the simultaneous existence of an earth fault and a failure
of the generator overcurrent sensor or the de-excitation
relay in the protection
scheme outlined in Appendix C. The tremendous arc damage that could result
14
from
such
a double
particular
protective
It
is
American
to be noted
in
the
that
of
R.A.E.
arcs,
but
a nwre
4
CONCLUSIONS
(1)
For
the
of
is
needed,
until
there
the
weight
prospect
the
vital
importance
would
of
had
a stabilizlng
was ln
the
voltages
the
the
200 volt
of
break
conversion
the
than
weight
1s a technical
of
namely
heavier
dc system
the
the
these
used
to
and
limit
effect
on the
used.
large
commercial
power
resulting
a weight
aircraft,
three-phase
conversion
components
in
and brushless
showing
British4
corresponding
through
equipment
the
resistance
have
considered,
to
between
The series
difference
due mainly
of
some difference
tests.
to be slightly
This
little
arcing
aircraft
ac system.
in
underline
is
experiments
proved
and
to
there
important
type
dc system
reduction
serves
devices.
results12'13
current
the
failure
a considerable
motors
advantage
there
is
over
the
ac system.
Furthermore,
frequency
the
invertors
equipment
It
(2)
with
a single
probably
considered
wire,
earth
control
and protection
circuits;
and by
is
avolded
in
the
the
that
return
event
of
drawback
tions
sustained
arcing
(4)
demand
lower
If
the
fuel
will
voltage
suitable
supplies,
of
incorporating
the
fixed
reliability
or variable
and
cost
of
be worsened.
the
in
use of main
A serious
to
equlpment
dc system
system;
and,
(3)
damage
consuming
to provide
would
is
most
no constant
particular,
line
diodes
may occur
than
speed
load
a generator
the
1s simpler
the
drives
sharing
are
less
of
is
required;
require
interruption
It
ac system.
complicated
the
supply
under
fault
to
loads
failure.
200 volts
with
dc system
a consequent
is
that
increase
in
the
risk
condiof
fire
aircraft.
pumping
and deicing
be considerably
(e.g.
50-100
reduced,
volts)
loads
become
in which
might
non-electric,
case
a dc system
show an advantage.
the
total
operating
power
at
a
15
Appendix
DESCRIPTION
OF THE SYSTEMS CONSIDERED IN THE WEIGHT COMPARISON
(see
A. 1
The 200 volts,
main
EBB via
even
consists
busbars
the
The four
of
of
one
channels
main
of
the
normally
to
aircraft
of
60 kVA,
an essential
load
with
busbar
can be met fully
channel.
singly
or up to all
emergency
via
each
connected
The total
generating
bars
channels,
the
generator
is
change-over
four
in
parallel.
installed
contactors
to
upon
feed
the
any one
loss
of
power.
For
ease
emergency
of
comparison
system,
four-engined
no load-shedding
although
flame
this
dc power
supply
rectifier
units,
two of which
connected
to
outer
fed
from
the
the
inner
etc.
A.2
200 volts
manner
fuses,
protection.
be required
the
bars
is
to
depicted
cover
the
on the
case,of
a
Such
from
connected
to
150 amperes
the
inner
main
Two transformers
to provide
system
but
it
components,
a change
obtained
of
a supply
of
transformer/
busbars
1400
and two
VA output
26 volts
are
ac for
(Fig.2)
ac one,
static
is
bars.
dc generating
to
i.e.
essential
dc system
The 200 volts
similar
are
essential
synchros,
The
may well
arrangement
out.
The 28 volts
and
bar
may be run
essential
(Fig.1)
generating
COC.
A 30 kVA hydraulically-driven
or all
four
contactor
loss
1)
ac system
MBB, each main
a change-over
with
section
three-phase,
The ac system
four
A
is
has been
has been
in
arranged
place
of
to
improve
channels,
each
intended
devised
the
to
function
in
to make use of
ac contactors
a
diodes
and logic
reliability
and simplify
control.
The system
of main
and essential
simplicity
unless
consists
of
there
dc control
is
when
it
essential
bars
will
required
four
busbass
via
it
a failure
machines,
functioning.
of
will
is
in
at
separate
intended
least
be necessary
continue
line
to
the
failure
of
all
four
all
causing
to split
the
The 25 kW hydraulically-driven
upon
run
power
50 kW, feeding
diodes.’
two,
to receive
of
Owing
the
channels
overloading
main
as long
bars.
power
to
the
in
of
sources.
generator
sets
relative
parallel,
the
However
as one generator
emergency
main
four
will
two sound
all
is
only
be
Appendix
16
DC transformers
inner
main
(26 volts
busbars
ac,
(28 volts,
and two
1400 VA) are
to
150 amperes
the
connected
outer
to
each)
are
connected,
essential
busbars,
the
essential
inner
and
two
two
bars.
to
invertors
the
A
17
Appendix
FACTORS INFLUENCING
Factors
poles
the
which
of
is
inversely
roughly
minimum
the
bearing
reliability
rotor
that
present
to
1.2
its
24000
lb/kVA
the
need
only
commutation
value
To meet
lt
is
of
the
estimated
alternator
and a given
speed.
number
of
Consequently
imposed
rotational
speed
for
a high
taking
into
by the
need
stresses
seals,
operation
resulting
for
an oil
for
the
rectifier
speed
imposed
in
cooled
for
upon
allow
in
for
of
the
alternator
x kW rating
of
the
dc output.
of
the
an alternator
shown
range
to power
which
the
kVA rating
requirements
practice
speed
ratio
can be obtained
for
of
have
of
alternator.
alternator
x kW rating
the
a weight
arrangement,
be 1.05
alternator
over
the
that
rating
speed
to
1.2
the
as possible,
but
overlap
estimated
as high
operating
system
factor
wave,
of
operating
and by the
possible,
minimum
full
commutation
life,
ratio
power
to its
be set
and oil
is
a three-phase,
perfect
a given
maximum
bearing
utilization
alternator
to weight
and diodes.
bearings
the
A high
should
windings
rev/min
at
power
for
on the
made on the
with
12000
speed
and long
with
2(a))
proportional
limitations
Tests
the
an alternator
operating
account
the
influence
The weight
THE DESIGN OF THE GENERATOR
( see section
'
B.l
B
the
kVA rating
This
dc output.
some loss
of
should
50 kW dc system
at
60 kVA weighing
choice
of
alternator
of
assumes
kVA due to
be increased
outlined
rated
by using
to an
in Appendix
72 lb would
A,
be
required.
B.2
Factors
In
voltage,
to
the
filter
influence
a dc system
which
basic
unit
1s essential,
frequency
which
appears
generated
is
inversely
for
the
to be high.
of
the
the
type
being
as a component
of
proportional
purpose
of weight
frequency
the
frequency
of
the
the
dc output
voltage,
is
proportional
the
weight
the
frequency
considered
Since
frequency.
output
to
saving,
for
of
the
of
the
ripple
the
alternator
ripple
ripple
voltage
voltage
output
it
Appendix
The output
where
n
speed
=
=
P
frequency
in
number
From this
alternator
1s given
by:
of poles.
it
can be seen
speed
and the
operating
speed
is
seen
here
is
the
revlmin
operating
and It
of
B
that
number
desirable
of
in
the
frequency
It
poles.
order
to be desirable
is
has
already
to minimise
for
dependent
the
minimising
on both
been
stated
weight
the
the
of
weight
that
the
of
a high
alternator
the
filter
unit.
The number
by its
the
diameter,
number
tors
of
which
which
itself
is
can be accommodated
limited
poles
is
a function
at
up to
24000
operating
8 and
12 depending
rotor
would
2400
of poles
on the
be suItable,
of
the
value
essential
to ascertain
supplying
a rectifier
rev/m~n
detalled
expression
given
alternator
rating
of
the
In
that
load
maxunum
the
at
and
of
is
determined
stresses.
operating
number
poles
For
Therefore
For
speed.
could
this
vary
frequency
range
frequency
can be finally
alterna-
between
application
an output
alternator
the
parameters
output
an alternator
supplying
r
L;
is
is
chosen
where
is
rectifiers,
the
the
phase
the
a 12 pole
of
1200
the
resistance,
2400
the
to
should
T is
the
that
values
of
its
magnitude,
The relevant
including
subtransient
than
time.
An
to be calculated
an alternator
affect
in
its
the
for
time
that
inductance
operation
switched
subtransient
since
time
from
of
50 kW
in
the
be acceptable.
which
efficiently
the
be greater
periodic
for
is
being
not
time
it
when
criterion
time
Hz would
alternator
to operate
the
direct-axis
of
found
settled
efficiently
conmutation
has been
frequency
of
operate
frequency,
rectifier,
and it
The characteristics
switched
mode
will
The commutation
L" must be small
and equal
in
P
conmutation
time must be short.
where
maximum
the
by Shillingllpermits
a maximum
If
when
rotatIona
requirements.
resulting
taken by a phase to commutate.
T
x for a three-phase
full-wave
B.3
the
rotor
Hz.
Before
the
by the
on the
mode,
inductanc'es
efficient
the
(L"
d
"2
operation
constant
of
that
is
given
rectifier,
=
Li'.
the
by:
is
and
Appendix B
19
The values of the subtransient
inductances can be reduced by at least
60% and made equal in magnitude by fitting
a complete damper winding on the
rotor, as shown by tests previously
reported 14 . Consequently for this application the alternator
would have to be fitted with a damper winding.
This would
not add a significant
amount to the weight of the alternator
but it would
introduce a difficult
design problem with regard to the mechanical stability
of
the rotor, owing to the high rotation21
speeds involved.
ES.4
Diode assembly
In order to obtain a high utilization
factor for the alternator,
a
three-phase, full-wave,
rectifier
arrangement is required.
The dzode assembly
would be Integral with the alternator
and the diodes would be liquid cooled,
the liquid being pumped through channels formed in the diode mounting ring.
For the purposes of the weight
diodes will
be required
comparison it
has been assumed that
to pass a maximum short-circuit
current
the
of 300% full-
load current (750 amperes) for 1.5 seconds and to operate in an ambient
temperature of 2OO'C when cooled by a liquid coolant having a maximum inlet
temperature of 165'C. To meet these requirements two 250 ampere diodes connected
in parallel
would be required for each arm of the bridge.
The combined weight
of the 12 diodes would be approximately 5 lb and allowing for the weight of
mountings, housing and connections,
it is estimated that the diode assembly
would weigh 18 lb.
For generators
of this
type the weight and reliability
of the diodes is
greatly affected by the coolant inlet temperature.
For example if in this case
the inlet temperature were reduced to 12OnC only one diode per arm would be
required and the need for selection
and pre-ageing the diodes might not arise.
B.5
Ripple voltage
filter
unit
Tests carried out on a high-frequency
supplying dc via a three-phase, full-wave,
alternator
(40 pole, 8000 rev/min)
rectifier
circuit
indicated
that the
unsmoothed ripple voltage of a brushless 200 volts
full-speed
conditions
could be as much as 70 volts
A filter
capable of reducing
the ripple
dc gknerator
peak-to-peak.
voltage
under full-load,
to an acceptable
level
could be made using the design methods developed by Hinton, Meadows and Caddy 15 .
The unit would consist of a modified low-pass filter
network in which the
inductance elements would consist of ferromagnetic
tubes mounted on copper rods.
For a 50 kW generator
the capacitor
would have to be capable of passing
Appendix B
20
approximately
20 amperes. The unit would weigh approximately
put ripple voltage would not exceed 10 volts peak-to-peak.
B.6
15 lb.
Type of alternator
Of the available
salient-pole
alternator
known types of machine the rotating
is preferred for this application,
weight to power ratio than any of the solid-rotor
speeds considered permissible
with the bearings
diode, wound field,
since it has a lower
types when operated at the
and oil seals presently available.
Should bearings and oil seals which permit the use of operating
over the range 24000 to 48000 rev/mln become available
the solid-rotor
would become more competitive
on a weight to
still
be Inferior
electrically
because their
mately three times greater than those of the
It would be essential
to fit the solid-rotor
Summary of estimated
It 1s estimated
made up as follows:weight
weight
weight
that
weights
speeds
types
power comparison, but they would
leakage inductances are approxiequivalent
rotating
diode machine.
machines with damper windings to
minxuse their pole-face losses and subtransient
inductances;
their rotors would no longer be simple homogeneous structures
tlon at the maximun stress limit of the rotor iron.
B.7
The out-
of generator
consequently
capable of opera-
components
the complete 50 kW dc generator
of alternator
to give 50 kW dc
of complete rectifier
assembly
of complete filter
assembly
Total
would weigh 105 lb,
72 lb
18 lb
15 lb
105 lb
Based on these estimates the weight to power ratio of an oil cooled,
brushless,
50 kW dc generator suitable for this application
is 2.1 lb/kW.
21
Appendix
C
PROPOSALS FOR SYSTEM CONTROL AND PROTECTION
(see
C.l
The use of main-line
On an ac system
and generators
diodes
from
In
placed
These
in
a twofold
(a)
the
and
faults,
circuits
; and
fault
generators
remains
Parallel
to
when
earth
fault
the
diodes
must
have
diode
individual
is
is
or
current
therefore
and
the
little
difference
in
A possible
busbars.
load
Thus,
itself
any
loads
connected
of
time
characterlstlcs
off
to
the
faults,
of
isolate
and from
need
for
discrimination
output
since
the
generators
Fig.2).
busbars
generator
when
the
main-line
the
under-voltage
since
of
underprotection
there
voltage
in
the
of
1s an
the
healthy
automatically
the
to the
dependent
are
more
means
first
generator.
until
a persistent
diodes
current
This
concerned
cannot
would.
until
could
when
circuit-breakers
on balance
in
the
of ;nain-line
of
disconnecting
The
the
fuses
penalise
compared
than
so that
generator
(or
busbars
upon
fault
come on
the
with
an
diodes
there
may be
and weight.
disadvantage
the
of
contactor
de-excited.
and isolation
size
case
main-line
the
and size
a positive
while
excitation
cable
However
overall
the
However
carrying
as weight
to 200 volts
of
the
(see
has been
transfer
provide
exciting
three-phase
busbars
feeder
generator
operational
of
busbars
adjacent
as an ac generator-control
as far
for
the
of
the
use of
correct.
be capable
be required
holding
made easier
voltage
fault
do not
by means
and
normal.
would
they
line
by the
the
problem
dc circuit-breaker.
that
onto
can be achieved
earth
obviate
the
cables
and instantaneously
on a generator,
arrangement
a period
since:-
therefore
their
ruptured
isolation
advantage
on a busbar
rupture
brought
conditions
generator-cable
operation
line
are
fault
cables
simplify
overvoltage
generator
automatically
and
they
the
in
generator
diodes
generator
voltage
under
the
2)
generators
a dc system
have
(b)
the
isolated
contactors.
diodes
section
while
will
the
is
the
the
being
last
generator
run
diodes
generators
up and is
is
of
speed
could
is
within
run
course
down)
conditions
and the
time
is
from
in
being
under-voltage
acceleration
period
the
generator
experience
engine
This
use
for
excitation
be shortened
its
normal
by
range.
Appendix C
22
If there were any loads likely
to be connected during this under-voltage
condition and likely
to be damaged by it, one solution would be to fit generatorsolution
control contactors and under-voltage
trips, but a simpler and lighter
might be to fit
under-voltage
trips
to the individual
sensitive
loads.
Size and weight estimates have been made for a main-line
diode assembly for
a SO kW generating channel which has to pass a continuous current of 250 amperes
and a fault
temperature
current of 750 amperes for approximately
1.5 seconds over an ambient
With each
range of -40 to +70°, at altitudes
up to 70000 ft.
assembly consisting
of three parallel
diodes relying on natural convective air
cooling from heat sinks, the approximate dimensions of the unit would be
22 in x 84 in x 8 in, with a weight of approximately
16 lb.
With forced cooling
the size of the unit could be reduced, but the additional
complications
in air
ducting or other forms of coolant circulation
would be such as to make any
overall weight saving unlikely.
Main-line
diodes with forced cooling could be
less reliable
than those wrth natural
cooling system.
c.2
Control 5
cooling
due to possible
failure
of the
With modern alrcraft
engines the speed range between ground idling
top speed is approximately
1:2. With ac systems at constant frequency
variation
is taken up in the constant speed drive, which however still
speed controlled.
Thus with ac systems there are two parameters which
be controlled,
i.e. the voltage and the frequency (speed), whereas with
system only voltage control is required.
and
the speed
has to be
have to
a dc
In parallel
sharing circuitry
operation the dc system is simpler since reactive-load
is not required.
Real-load sharing may still
be necessary
with a paralleled
generator.
dc scheme, depending on the load-droop
characteristics
of the
The voltage regulator for a dc system may have additional
complications
over that used on a constant-frequency
system because of the speed variation
of
the generator.
It is usual to provide the power for both control and protection
from a separate permanent-magnet pilot exciter mounted on the same shaft as the
main machine. With the constant-frequency
arrangement the pilot exciter output
is constant in voltage and frequency.
In a dc system the generator speed will
vary and thus both voltage and frequency of the pilot-exciter
output alters
accordingly.
Brushless generators are themselves two-stage devices and the
incremental gain from the main exciter field current to the output voltage is
Appendix
C
approximately
term
of
mental
proportional
the
pIlot
gain
of
exciter
the
some complexity
Some of
slmllar
in
protection
lined
in
fuse
the
in
squared.
design
of
The added
a speed-cubed
comblnatlon.
e.g.
term
in
To counteract
the
dc voltage
The
It,
protective
automatically
indication
needed
speed-dependent
the
this
overall
speed
incre-
effect
adds
regulatorh.
busbar
large
and
this
devices
are
not
achieved
1s still
is
direct
cable
isolated
of
currents
should
present
by means
necessary.
on the
of
the
In
by
the
the
scheme.
main-line
are
generator
earth-
the
dc system
out-
of
on the
by
the
bus-
faulted
the
use
of
difficulties.
under-frequency,
dc
system
and
can be achieved
no great
a dc
rupturing
generator
as over-frequency,
requred
an ac and
protection.
de-excitation
of
on both
over-current,
and busbar
and by
sensing
sequence
Price)
A a faulty
amp1Lfiers5
and phase
devices
over-voltage,
(Merz
feedlng
Such
voltage
protection
Appendix
channel.
magnetic
the
nature
fault
is
speed
results
machine
to
the
Protection5
c.3
tle
to
under-voltage
Under-voltage
diodes,
though
protection
under-
24
Appendix D
SURVEYOF METHODSOF SWITCHINGFOR 200 VOLT DC SYSTEMS7*8.g
(see section
General principles
D.l
of current
interruption
There appear to be two alternative
current
2(b))
basic
principles
for interrupting
the
in any circuit:-
Insertion
of an increasing impedance into the circuit
by means of
(i)
a switching device.
This principle
is employed in & purely mechanical switchgear and in certain types of solid-state
switch, such as those using transistors.
(ii)
Reversal
of the voltage
across the switching
device,
so as to
achieve complete electrical
isolation
in it when the current through it falls
normally employed in s switchgear because of
to zero. This is the principle
the natural periodic reversal of both the voltage and the current in the circuit.
In dc circuits
there are no natural current zeros, but voltage reversal can be
achieved by connecting a charged capacitor across the switching device, a
This can be applied to x-type
technique known as 'forced commutation'.
mechanical contacts ox- to thyristors.
D.2
Switchgear
required
in 200 volt
dc systems
The switchgear required in a typical
200 volts dc main power-distribution
system (such as Fig.2) is minimal, and consists only of a ground-power contactor
GPC and an isolating
or 'on line' contactor to separate the paralleled
channels.
In addition,
the load circuits
will require contactors or manually-operated
switches or circuit-breakers,
just as in normal 115/200 volt ac systems.
If
it should prove unpracticable
to develop small dc circuit-breakers
with adequate
fault-rupturing
capacity,
and clearance times sufficiently
short to protect
the diodes in the system, then a fuse would be needed instead, together with a
manual switch
if
A new family
connect/disconnect
facilities
of switchgear
would therefore
were also required.
be required,
capable of handling
normal load currents ranging from about 1 ampere to 250 amperes, in ambient
temperatures between -4O'C and +85'C and at altitudes
of up to 70000 ft in the
worst cases. A moderate overload-rupturing
capacity of a few hundred per cent
would normally be essential
as a bare minimum. In addition an ability
to
rupture high fault currents would be required of certain
of fuses or main-line
diodes should prove unacceptable.
switchgear
It
if
is desirable
the use
that
25
Appendix D
load switches
For isolating
shall be capable of switching
contactors this is essential.
and a similar
endurance of 50000 operations,
gear.
D.3
Types of switchgear
D.3.1 Purely
mechanical
for 200 volt
currents flowing in ather direction.
Modern ac switchgear has an
figure
1s desirable
for dc switch-
dc systems
switchgear
The simplest types of dc purely mechanical switch are the unsealed airbreak types.
These achieve current interruption
by using either deion grids or
multiple
gaps to create a number of arcs in series requiring
a total arc voltage
greater than the supply can maintain.
For low rated currents,
of the order of
10 amperes, the multigap type, employing eight short series gaps, is the more
suitable.
Careful mechanical design, manufacture and assembly are needed however to ensure that the eight pairs of contacts open practically
simultaneously
in order to minimise the arcing times and achieve maximum endurance.
For high rated currents,
of the order of 100 amperes, an unsealed multigap switch would require ten series gaps, with the possible addition of main
bridging contacts to reduce the total contact volt drop and the heat generated
This would involve a rather unwieldy construction,
and
in the contact block.
the problems of mechanical design and tolerancing
would be more severe than for
the smaller ratings.
The "se of four long gaps fitted
with deion grids is
thought to be a better proposition,
particularly
if grid designs can be improved.
With either type, however, arcing tends to last rather longer than in 400 Hz ac
switchgear,
so it may prove difficult
to achieve contact endurances of 50000
operations on dc working, particularly
since metal transfer will in most cases
be unidirectional.
Nevertheless both types are basically
bidirectional
(so long as permanent magnets are not used to provide magnetic arc deflection)
and both have the ability
to rupture very high fault currents.
The use of oil or compressed air or nitrogen in a sealed contact
enclosure should enable a rather more compact and lighter
contact assembly to
be used. However, a considerable amount of development work would be required
to determine the possible overall weight saving and to establish
adequate seal
integrity.
A type of sealed switch which has been commercially developed
recently is the dry-reed switch.
It can be used in the 200 volt dc system
for currents up to 0.5 ampere, but little
extension of the simple reed
structure
beyond this dc rating can be foreseen.
Appendix D
26
D.3.2 Use of solld-state
devices
having a natural
turn-off
ability
Neither transistors
nor gate-controlled
switches can provide feasible
200 volt
dc switches at present, since they are not available with VCBO
voltage ratings
in the system.
which can withstand the transient
switching surges expected
Even with Increased voltage ratings,
the current ratings of
gate-controlled
switches and pnp transistors
(for which control circuits
for
negative-earth
systems are much simpler than those for npn types) are at present
llmlted
to only a few amperes. Both devices also possess limited
overloadand fault-rupturing
capacities,
and would require relatively
high control
POWXS.
D.3.3 Mechanical
switches
and thyristors,
with
forced
commutation
All the remaining feasible methods of switching 200 volts dc power involve
forced commutation, but this has several drawbacks. A large and heavy commutatlon capacitor is required, the size of which is directly
related to the
highest overload current which the switch must*be capable of interrupting.
Short-circuit
fault currents cannot be ruptured and a fuse must be included
for this purpose.
The switch is suitable only for unidirectional
current flow.
The detection of the true state of the switch for indication
and interlocking
purposes IS not achieved as readily as with purely mechanical switchgear.
In
when turning off the thyristor
the thyristor
switch, the commutation circuit,
by means of a reverse voltage, imposes an overvoltage across the load of up
to 100%. The heat generated
t
in the thyristor
by the load current demands a
owing to the low density and the
very large heat sink, if cooled naturally,
high temperature of the cooling air, and the relatively
low maximum junction
temperature permitted
(125-150'0.
Nevertheless the thyristor
does provide a
purely static
switch with no moving parts to wear out.
It can therefore offer
a very high endurance, provided that its components are carefully
chosen and
conservatively
rated to stand the unfavourable electrical
and thermal
environment.
The addition of mechanical back-up contacts to the dc thyristor
switch
would enable the steady-state
losses and the heat sink to be eliminated,
with
a considerable saving in weight.
The development of thyristors
with shorter
turn-off
times will reduce the weight and size of the commutation capacitor,
and might make this hybrid type of switch competitive,
in respect of weight
and volume, with the purely mechanical dc contactor.
Even so it would still
be more expensive, it would induce very high spike voltages in the system, and
would possess the many operational
limitations
of forced
commutation.
h
Appendix II
A further
27
disadvantage
is that failure
of almost any component, including
failure
of the back-up cont&ts
to make, would res‘ult
would be impossible to switch off the load.
D.4
Estimates
of weight,
in a situation
where it
volume and cost
In order to make quantitative
comparisons between the various types of
dc switch, estimates of weight, volume and cost have been made for two
representative
continuous ratings:
10 amperes and 100 amperes. The environment
specification
Includes ambient temperatures of up to 85'C and altitudes
of up
to 70000 ft.
The 10 amperes switch would be manually controlled,
and equivalent
as far as possible to conventional modern 115/200 volts ac aircraft
leveroperated switches.
The 100 amperes switch would be remotely controlled,
and
equivalent
as far as possible to conventional modern electro-magnetically
operated 200 volt ac aircraft
contactors.
Weight, volume and cost estimates
have also been made for ac switchgear of the same real-power handling capacity,
assuming power factors of 0.8.
All the estimates are summarised in Table 1,
and it can be seen that the lightest
and smallest type of dc switch is the
purely mechanical one. Even so, the weight, volume and cost penalties
of small
200 volt dc lever-operated
switches when compared with their ac equivalents
are
approximately
100%; for large 200 volt dc contactors the penalties
are
approximately
50%.
The problems of designing
small
dc manually-operated
circuit-breakers
However, assuming that it is possible
have not been studied in any detail.
avoid flash-avers
in a compact switch when rupturing
fault
altitudes,
the weight penalty is estimated at approximately
currents
75%.
at high
to
28
Appendix E
TYPES OF POWERCONVERTOR
PROPOSEDFOR MOTORSAND SECONDARYDC SUPPLIES
(see section
E.l
Electric
motor drive
2(c))
units
A dc commutator motor could be energised directly
from the dc supply
without the need for a" Intermediate
stage of power conversion, and would be
However the use of a continuouslylighter
than a combined ac motor and invertor.
running dc conrmutator motor operating directly
from the 200 volt dc line would
not be regarded as acceptable in high-altitude
aircraft
due to the danger of
flashover,
abnormal brush wear, and the cost of brush and commutator maintenance.
A brushless type of motor would therefore be required for such applications.
The invertor-fed
ac induction motor would appear to be the best choice for
brushless motor drives since the motor itself
is cheap, robust, highly reliable
and is the lightest
type of ac motor.
The only serious alternative
to the ac induction motor would be what is
commonly referred to as the 'brushless dc motor', i.e. a permanent-magnet
synchronous type motor, which, like the ac induction motor, would require a dc
to ac power convertor.
Besides this it would also require some form of rotorposition
sensor to simulate the function of the commutator of the dc motor,
would xxrease its cost.
Whilst the brushless dc motor might offer some
marginal advantages over the ac induction motor in the smaller fractional
power sizes, the induction motor would be cheaper and would have a better
to weight ratio in the larger sizes.
which
horsepower
When supplled from a square-wave source the induction motor has been
shownl' to function satisfactorily
and with negligible
loss of performance as
compared with that obtalned on a sinusoidal
supply.
The relatively
unsophisticated
square-wave invertor would the" suffice for motor supplies.
It 1s a normal characteristic
of electric
motors that the starting
current
is much higher than the normal full-load
current.
The associated invertor must
either be designed to provide this heavy current at a considerable weight
penalty, and with a poor utilization
factor under normal running conditions,
or
have some form of control to limit the current on starting.
To limit the
starting
current of a dc motor would result in a decrease of starting
torque,
but in the case of the induction motor, by initially
reducing the input
frequency and voltage,
the starting
torque can be increased whilst the starting
current
is reduced.
Appendix
E
29
Cooling
of
high-altitude
its
air
aircraft
density
weight
thyristors
is
density.
permitted
rapldly
and
the
the
required
invertors,
forced-air
Forced-air
cooling
may have
motor
heat-sinks.
Based
curve
of
Fig.3
and
temperature
a motor
designed
weights
of
In
deliver
be rated
some applications,
loads
of
for
such
peak
The weight
low-altitude
E.2
data
to
thermal
At high
of
except
convective
for
cooling
be used.
as the
to draw
the
low-power
must
drives
be used
by both
show the
invertors.
the
air
over
invertors
of
manufacturers
relationship
The curve
=
the
invertor
of
10000
e.g.
flying
some 3 to
fuel
for
and R.A.E.,
between
the
square
the
wave
(kVA) o’55
8.2
would
weigh
lb.
about
1.6
times
as much as
rev/min.
controls,
4 times
the
the
normal
motor
load
is
and
required
the
to
invertor
must
loads.
are
conditions,
based
with
on a maximum
natural
ambient
temperature
of
70°C under
cooling.
DC transformers
The dc
transformer
rectifiers,
and,
components,
in
Invertor
transformer
at
comprises
when required,
particular
the
a square-wave
a filter.
of
would
approximately
transformer/rectifier
unit
it
approximately
(TRu).
is
3 kHz.
the
Larger
invertor,
In order
transformer,
a frequency
weigh
the
high.
and estimates
weight
a speed
peak
that,
for
maximum
temperature,
in motor
also
too
to
effectiveness
be used
not
the
by:-
applications
for
could
constructed
Invertor
normal
is
work
can be represented
In most
which
falling
infinity.
liquid
and
applications
approach
burden
7O’C)
heat-sink
heat-sink
convenient,
may conveniently
has been
the
fan
due
the
high-speed,
and with
(125-15O’C)
then
a severe
the
below
can be assumed
where
(over
high
well
limiting
would
is
In aircraft
density,
it
represent
cooling
fuel
air
and
own cooling
the
area
of
to be kept
the
in
temperature
heat-sink.
approach
or,
on experimental
kVA ratngs
invertor
its
if
and the
cooling
Liquid
pump drives
thyristors
the
problem
and therefore
ambient
of
reduced
may not
area
has
reduction
a severe
tempekature
temperature
surfa&
1s considerably
air
increasing
may well
the
is
surface
junction
heat-sink
due to
cooling
with
temperature
altitudes,
ambient
temperature
between
ambient
invertor
The heat-sink
junction
the
the
the
The heat-sink
impedances
the
when
low.
increases
in
a transformer,
to minimise
desirable
At
this
to
the
weight
operate
frequency
the
a 1 kW dc
same as a similarly-rated
TRUs are
often
designed
of
400 Hz
with
forced-air
Appendix
30
cooling
of
ratio.
Forced-air
(unless
required
the
the
transformer,
cooling
transformer
while
the
weight
of
ratings,
is
only
invertos
may not
of
the
blower
motor
dc transformers
are
ratmg
the
falls
the
basis
in
a typical
of
the
of
particular
safety
increasing
3 kHz to
equivalent
equivalent
weight,
to
in
the
TRUs.
In
ac-fed
ratio
since
total
mainly
Therefore,
weight/power
weight
comparisons
but
specifications,
dc system
there
the
of
added
larger
the
lower-
power
packs,
power
packs,
invertors
can really
generally
would
the
commutation
appears
margin
sequence
it
as their
only
be made on
can be expected
be an increase
across
a voltage
thyristors.
and ensure
that
It
the
In the 200 volt
dc system
x V max'
440 volts
are envisaged
under abnormal
volts
owing
its
electronic-equipment
their
would
reduce
be required.
Since
transformer
is
in weight
that
in
2.3
practice
are
respect
rated
for
to
fast-turn-off
at
of
thysistors
operate
thyristors
the
a
least
surges
so that
desirable
times
to allow
line-voltage
conditions,
is
approximately
normal
thyristors
it
weight,
of
transient
2.5
1100
in
dc transformer
dc transformers.
voltage
small
than
and accurate
200 volt
During
heavier
of
be reduced,
used
the
environments)
fraction
than
weight/power
to
high-altitude
a small
be heavvar
the
Fig.3).
detailed
use of
supply
again
in
any benefit
own invertor.
be widely
steeply
(see
More
would
fairly
and/or
and its
would
a reduction
to be of
contributes
which
to
unlikely
itself
ratings,
owing
in
high-temperature
dc transformers
power
results
for
weight
the
which
E
up to
rated
invertors
(eg.8
at
at
US) would
needed.
The requirements
compatible,
is
the
If
being
and suitable
suitable
increased
frequency.
fast
turn-off
thyristors
attributes,
thyristors
1100 volt
devices
transformer
but
cannot
with
weight
and high
are
made by one manufacturer
required
to use
of
to
at
the
not
select
time
owing
currently
from
then
turn-off
to
the
are
available.
none
has become
the
invertors
to run
These
the
not
An attempt
thyristors
times.
need
voltage
production
of writing
be obtained
longer
reverse
must
would
invertor
having
available.
be designed
give
at
an
a lower
be
31
Appendix
F
WEIGHT COMPARISON BETWEEN 200 VOLT AC AND DC SYSTEMS
(see
In
order
Concorde
result
should
get realistic
figures
it was decided
to base the comparison
f
However it must be borne
in mind that
the
electrical
system.
not
study
equipment
2)
to
on the
detailed
section
of
design,
be regarded
as speciflcally
all
of
aspects
would
for
a change
from
be necessary
before
the
electrical
Concorde,
because
ac to dc power,
attributing
a much more
including
figures
to
consumer
a specific
alrcraft.
As already
of
necessity
keep
the
stated
many estimates
exercise
circuit
and
picture
of
layout,
equipment
It
Concorde
withln
every
the
has
full
of
effect
circuits
the
layout
assumed
that
will
still
ment
and cables
been
will
assumed
which
control
amount
of
for
certain
change
in
omltted
from
unchanged
whatever
the
type
of primary
including
C.S.Ds.,
detailed
in
Tables
The quantity
estimated
to
into
the
large
three
switches.
has been
In
total
and
sizes
2 and
switchgear
the
total
variety
of
200 volts
a similar
weights.
used
in
in
be identical
the
weight
ones
comparison
that
all
both
and
that
cases
ac and dc.
and
utilisation
as it
It
26 volts
equip-
considered.
comparison
power
on circuit
200 volts
cases
an accurate
required.
for
at
only
The
will
remain
source.
electrical
systems
switchgear
and cables
in
the
shown
Concorde
as a breakdown
switchgear
For
to each
this
In both
are
the
used
figures
- protective,
the
of
to
every
can give
still
order
of
have
and
in
Figs.1
and motor
and
2,
investors,
are
3.
classes
added
cable
utilisation
of
from
basic
ac power
unchanged
will
weight
study
power
purpose
services.
is
the
a detailed
400 Hz ac power
dc system
of
the
of
complex
to be made in
ac to dc will
amount
for
28 volts
The weights
from
extremely
had
electrical
fundamentally
and switching
be required
using
the
remain
a small
Only
a change
or even
therefore
also
that
is
have
limits.
equipment
design,
utilisation
cabling
and simplifications
reasonable
piece
system
used
relays
dc system
has
not
be obtained.
has been
grouped,
for
or contactors,
and
it
a suitable
could
ac system
percentage
had
to be
Owing
simplification
lever-operated
weight
increase
class.
way the
ac cable
Furthermore,
Concorde,
weights
owing
a simplification
to
have
had
the
large
has had
to
be estimated
variety
of
cable
from
the
types
to be made by choosing
a
is
32
Appendix F
single cable of suitable rating and size for each circuit,
based on the circuit
current and the numbers of cables bunched together.
Cable ratings due to
bunching have been taken from B.S. Specifications16*17p1a
for standard cables
and have been applied, for ac, to nyvin 10 and larger as three cables bunched
or to minyvin 12 and smaller as twelve cables bunched; for dc,' to nyvin 10 and
larger as a single cable or to minyvin 12 and smaller as twelve cables bunched.
It
is also possible to reduce the size of wiring to some 115 volts,
singlephase, ac equipments when the voltage is increased to 200 volts dc. Only items
consuming more than 460 VA (4 amperes) will benefit as the minimum practical
size wiring would already be used where the consumption is less than 460 VA.
The need to use 200 volts dc brushless drives for all continuously-running
dutres such as fuel pumps, fans etc. will incur a weight penalty by the addition
of square-wave invertors
to the existing
simple, ac squirrel-cage
induction
motors.
Table 3 therefore records only the weight of such invertors.
Services such as engine and intake controls,
instruments,
navigation,
radio aids,
etc., when supplied by a 200 volt dc system, will require dc
transformers
and invertors
for their internal
needs. An estimate has been made
from the prototype Concorde electrical
load sheets of the amount of dc power at
other than 200 volts,
and the amount of 200 volts,
three-phase,
400 Hz ac power,
which would be required thereby.
This is shown in Table 4 in the form of the
amount of power, both ac and dc, which would be required from each of the four
main and four essential
busbars.
Under the heading of ac invertors
is also
given the estimated weight of the separate invertors
needed to supply such power
from each bar, while under the heading of dc transformers
is given the number of
equipments fed from each bar with their total power requirement and the estimated
increase in equipment weight due to the use of dc transformers
within the units.
Table 5 gives
the total
weights
of the 200 volt
ac and dc systems,
derived
from Tables 2, 3 and 4. The figures given relate only to the primary power
system.
When the circuits
and systems unaffected by the change in the primary
power system from ac to dc (such as the 28 volts dc power system and many of
the utilisation
circuits)
are added the total electrical
system weight rises
(in the Concorde) to about 7600 lb.
This includes 3500 lb of cable and 1600 lb
of fixed installation
fittings,
i.e. clips, ducting and panels.
The weight of
the secondary systems is unaffected by the change in the primary power system
from ac to dc.
Appendix F
F.l
The use of fuses instead
33
of manual circuit-breakers
In Concorde, manual circuit-breakers
are used at the busbars for
protecting
utilisation
circuits;
this is quite usual in civil
aircraft,
although fuses are favoured in military
aircraft.
The different
outlook is
due mainly to the fact that in civil
aircraft
it is usually easier to provide
more accesstble siting of these items, for resetting,
than it is in military
aircraft.
Unless resetting
can be undertaken in the air, the general use of
manual circuit-breakers
is unwarranted.
A direct comparison of ac circuitbreakers with their dc equivalents
shows that the latter are 49 lb heavier
(113 -(27.7 + 36.6) lb, see Tables 2 and 3). However Table 6 shows what happens
to the weight of the utilisation-circuit
protective
gear when fuses are substituted,
wherever practicable,
in both the ac and the dc systems (manual
circuit-breakers
having to be retained for the three-phase circuits).
The dc
fuses are now 25 lb lighter
than the ac.
Table 7 gives a breakdown of the weight differences
the dc systems, with the two methods of utilisation-circuit
between the ac and
protection.
34
Appendix
G
ARCING TESTS4
(see
An arcing
using
gap of variable
replaceable
initiated
brass
by fusing
method
was not
which
a number
power
was a Type
phase
bridge
of
The current
given
find
the
gap,
to
as one
current
time
is
to
while
for
the
With
with
right
to
fouling
frequently
it
used
For
at
more
suggests
to
the
this
left
400 Hz,
gap down
to
l/16
envelope
line
ac supply
inch
of
even
this
it
the
was not
at
is
altitudes
were
in
or,
are
for
a sustained
possible
up to
to
that
plotted
so that
liable
a
inspection
dc tests
of
case.
of
at
since
persists
found
each
somewhat
which
is
used.
a range
defined,
points,
arc
line
try
seconds,
the
a sustained
and above
lines
be formed
an arc
of
1 ohm.
to
arc
of
electrodes
a three-
200 volts
could
that
Results
upper
with
two
to
three
This
The source
altitude,
than
were
a negative
of approximately
arc
the
to repeat
ac tests
A sustained
for
of
conjunction
the
a given
altitude.
the
in
gap was regulated
indefinitely.
is
and
Arcs
two electrodes.
as significant.
resistance
oscillograms
and below
a 200 volt,
owing
a sustained
persuts
line
conditions
any
which
minunum
to persist
The broken
tions
at
that
and voltage
likely
Fig.4.
an arc
the
probably
was either,
maximum
find
the
by a series
procedure
the
them
chamber,
diameter.
to
dc tests.
across
1 inch
wired
accepting
the
of
a high-altitude
foil
alternator,
for
was limited
arbitrarily,
of
before
voltage
The test
to
to replace
rectifier
up in
electrodes
reliable,
times
2(d))
was set
of aluminium
158 aircraft
The open-circuit
gaps
strips
necessary
result
length
cylindrical
completely
made It
section
for
in
condi-
be formed
arc
is
to
80000
unlikely.
sustain
ft.
35
Table
ESTIMATES OF WEIGHT,
1
VOLUME AND COST FOR DC AND AC
SWITCHGEAR OF EQUIVALENT
Rating
Ambient
temperatures
Altitudes
up to
Type
of
grid
only,
+
Excludes
cost
E
5
2.2
45
1st
4.0
580
21+
back-up
1.4
27
21+
switch
0.11
1.7*
2.4
4.0
96
120
forced
forced
Thyristor
ac
Volume
in3
3.3"
(4 gaps)
Mechanical
with
commutation
Thyristor
contacts
25 kVA,
with
Lever-operated
Deion
Body
0.22
Thyristor
200 V, 100 A,
20 kW, dc
ft
Weight
lb
switch
Mechanical
with
commutation
115 or 200 v,
2.5 kVA, ac
*
70000
(8 gaps)
Thyristor
contacts
!OO V,
up to 85'C
I I
I I
Multigap
ZOOV,lOA,
2 kW, dc
RATINGS
excluding
assembly
with
back-up
Contactor
240
20
1700
16
420
2.8
operating
costs
11
lever.
and overheads.
63
69+
150-200+
160+
80
36
EQUIPIBW
WEIGHT FOR THE 200 VOLT. lliREE-PW+~.
current
amps
Ewpment
oenemtlng
Constant-speed
drlw
CcnWnt-spaed
drive
Ceneratcr
60 kVA
Control
and regulator
lhnsfonaer
4
26 V three-phase
ac l&B0 VA rau~l
28 V de
Alternator,
30 kVA emergency
Xrcult-breaker,
single--Se
-1
Witch,
““/off
(C.&D. disengage)
wtch,
on/off
(B.T.c.
0pew.e)
iwltch,
““/off
(eukx~“cy
ch?i”kx~er)
:a”trc1
u”lC &zxund power, phase sesuence)
175
75
35
::
118
f:
25
54
output
15C
output
85
15
10
10
10
-
:ebles
iable
102‘ w.1”
table
fable
:able
:abls
:eble
iable
for
for
for
for
for
for
79
2.5
85
8
175
unit
vnlt.
wt
lb
4
44
ccnti-cller
rectlfler
U"lC
o.ua"t1ty
alternators
175
instnrments
ground pcwer
dlstrlbutlc”
(sub-feeders)
lRU supply
emergency generator
transfo~~~~
115126 v
175
25
14.5
86
13
lrc”ltbreaker,
single pole
lrcult-break?er,
thr.x-wle
ontaotors
and relays,
various
witches.
le,w-cpB~ted,
-raricus
1” utlllsatlc”
4
:
4%
12.0
12.4
5.2
2.6
2
0.33
3.11
k::
4
15.5
62.0
1
55
0.092
0.05e
0.092
o.ose
5.0
55.0
0.2
0.4
0.4
0.4
5.0
t
:
1
Cable
&
unierglas
Nyvlnal
Hlnyvl”
NW"
MlnyVl”
Mlnyvl”
NyPi”
Mlnyvl”
c1rou1ts
3 to 35
1 to 35
2 to 60
10
316
10.0
344
32
125
3.0
3.1
1.3
0.33
m per
100
0
00
22
0
12
12
6
12
39.0
20.2
0.34
37.6
2.36
2.36
10.7
2.36
TOTAL
Srs1tchgear
Total
Nt lb
system
ccntactoor.
current
tmnsfcwrS
three-phase
Ccntactcr,
three-phase
(De-ice lsolatlo”)
cc"tactcr,
three-phase
changeover
"ontactor.
three-phase
for lRu
:lrcult-breaker,
three-plta.9
manual
Jlrcult-breaker,
WaIsfomer,
AC SYI3T?Il
187
267
10
21
30
23
34
7
1500
(ac only)
3ol
111
185
157
0.0%
0.33
FmmO.C!@
To
2.9
27.7
36.6
62.6
Fmm 0.052
To
0.198
20.3
TOTAL
147.2
37
Table
2
(Contd.)
-C”rre”t
unit
pU3”tity
Cable
1” utllisatlo”
Rain
dlspersll
Windscreen
anti-ice
Wing
and Intake
de-Ice
Wing
rind Intake
mts,
Wing md intake
!mtss
Cable
&
clrcult
supply
cyclic
co”tlmous
Air
Intake
sensor
heater
Wlndscree”
heater
Illndow
de-mlstlng
En&m
feed
pimps
(2.5 k-J/i)
I,“:”
tank pumps
(2.5
kVA)
lYlm
ms
(5.b
WA)
!%av?r.ge
and No.7 tank
pumps
Fuel
flow
and reheut
(ssm
map display
High
rmwmcy
51.5
single-phas
Si”gll+phaS¶
three-phas
12.3
11.0
2.0
(1.2
kVA)
50% total
three-phas
ChIW-phase
three-phasa
as three-phase)
thrse-ph¶SZ
three-phase
three-phase
d”“ildlCy
Fans,
Fans
three-phase
thm?-pha.¶
la--2e-plase
;md
2 forward
and
Inertial
Reheat
platform
l@tlo”
Lmdlng
lap
hX1
Lmip
Cobl”
1ntaks
iiE.5
rear
heater
lights
SupplIeS
::z
16.8
3.5
0.84
0.72
0.46
0.94
14.4
5.1
lllnyvi”
fl
Nyvl”
u
0
"
11
Nyvl”
Mlnyvl”
”
”
”
three-@lase
single-phase
31”g1e-ph4se
slngle-phas?
2.9
“22
1)
single-phase
:;
s1”gle-phase
7.0
0.7
5.2
.
5.2
0.34
14
10
10
8
1.59
20
22
22
22
"
N
11
‘1
22
14
22
14
14
10
nl”w” ”
1 .l
Total
wt
lb
wt per
100
”
three-phase
Loran
3 forrerd
3.4
9.6
ChlW-phea,
ri-nxl-pham
three-phas
three-phase
three-ph¶se
1%
lb
=JPS
22
12
32
22
4.33
4.33
6.67
1.59
0.34
1.59
1.59
4.33
0.51
0.34
0.34
0.34
0.34
2.36
0.51
3
7
102
107
52
21,
3
z
34
%
1.5
1.5
1.5
2.0
0.34
8.0
1 .o
23.0
15.0
02.3
u
16
14
”
a
”
20
0.34
0.97
1.59
0.51
0.51
‘I
20
0.51
TOTAL
20’
611.0
._-__
Co”tl”uously
nmlng
EnClne
feed
pimps
(2.5 kYA)
lbl”
t”“k
puups
(2.5
Mm)
Trim
nrmps
(5.8 kVAI
SXVP”~~
and No.7 tNIk
pla,,ps
(1.2
Wns 1 rind 1 fonvlrd
Cl-no VA)
Qns
3 for-m-d
and rear
073
VA)
,“c”m
lrrmp (58 VA)
:.T.S.
fuel
Jl"dScr.ze"
ptmp
vrlper
(400
p”mp
VA)
(117J VA)
motors
kVA)
12
12
4
6
Identical
both
4’
2
2
2
inv-ertor
give”
ac motors
used on
and dc.
Addltlonel
w1mt
Ior
do SUPPIY
in Table
3.
ac
38
EQUIPf'XNT
WEIGHT
FOR
'IlIE
200
VOLT
"2
SYSXN
unit ti
Qua”tlty
lb
250
105
a
1
250
1 at
1 at
tbme
,Co"tactor.
,:ontaccm.
shgle
pole
s1ng1e
pole
pole
(ror
de-Ice
lsolaclo")
2.3 v
I
i
for
ror
c lable
CL&able for
c able ror
C able
r0ic able
r0r
C able
r0r
rain
&?“emMrs
2%
l"stm,,e"Cs
!awnd
pomr
dlstribuClo"
dc u-msro~rs
2%
35
25
8.5
125
(sub-reeders)
in~emr~
ecmrgency
generator
1
2 at 155
130
30
250
35
200
50
25
15
150
O"Cpllt,
54
O"T,pUC
125
c :ables
c :able
switchgear
onual
clrcult-braalters,
C ontaccors
s
witCheSt
sl”gle
and relays,
1” ut111Sat.i
pole
var10us
various
leveropmted,
7
15
15
5
20
1.8
16
64
c1rCuit.5
1” ut11islt10”
ru ai” dlsparsxl
’ WI 1ndsix-e"
anti-loo
W: lug and l”tak0
&-ice
1111”~ and 1”talB
mats,
I
supply
~yello
0.1
$3
103
1
60
wt. per
ta,
60
Cable
g&
uniergu.3
Ny-vlnal
0~
LXX
223
22
cc
48.9
n1”wn
Nyvin
Nyvl”
Nyvl”
llnyvl”
ml”
1C
:;
4
0.34
4.33
4.33
1.59
16.9
a.2
109
3.5
9.1
16.5
i
13.9
4.8
17.8
1113
1VdCO”lyl
? to 80
185
75%
1”0masa
50%
l”Cr-=aS
157
lL%,
Cable
-Slzd
5.9
16.7
80.0
70.0
2
0.3
53
412
clrcu1ts
28
2
I CO iu
10
7.2
3.5
0.5
0.3
0.07
0.07
22
lUTAL
cab10
32
a
7
?QTAL
n
420
1at1S7
t:oncactar,
DlOde
mode
Ixuse size 5
I wuse Sk.3 2
I?use size 0
I?uuB s1z.e 0
/De Transrom?r,
2w
?a
rotalwt
lb
Ml”yv1”
NYv1n
NJ-h
NH”
113
SB
40
a6
wt pl‘
100
18
10
8
a
z3
6.67
6.67
2.1
8.0
p5
i
s
39
se3
(Contd.
)
C”ITl2”C
Equlpnent
amps
U”lC
lb
Quantity
wt
Total
wt
lb
-Cable
in
uLlllsaLl””
circuits
(Contd.)
Wlw
and Intake
mats,
co”tln”ous
Windscreen
heafer
Air
illtake
sensor
heater
Wlndoiv
de-mlsrlng
89
6.7
7.1
3.5
Nyvl”
ninyvin
nl”yvl”
n1”Yvln
En&Z
reed
lumps
(2.0
!4J)
l!al”
tanY
pumps
(2.0
IdJ)
him
prmp
(4.7
w
111
Szave”@
and Ho.7
tank
PULPS (0.95
l&l)
““el
flow
<x,d reheat
klssume
50% t.OL~l
II*. 200 Y dc)
iZap dlSpl2.Y
ilgi-,
rRquency
L.or2n
Hlrmldlty
'a-IS,
and2
r0lwdrd
pans 3 romard
and mar
10.0
1G.O
23.5
4.8
1.4
!:lrJ"l"
lll”Yvkl
wvl”
n1nyvin
!‘l”;rvl”
1.0
0.64
1.3
25
7.1
1.5
lllnyvl”
22
:11nYvin
22
Ill”wl”
22
Nyvl”
10
l?l”yvi”
16
Xl”yv1”
22
0.34
0.94
0.>4
4. J3
0.97
u.34
Mlnyvl”
Ml”yv1”
Hl"yvl"
nl”yvl”
Mlnyvl”
Hl”y”1”
Ml”Yvl”
V”rlO”S
0.51
0.34
0.51
0.34
0.34
0.34
0.34
Inertial
platrorm
@heat
lgnlclo”
LmdlW
lamp
hxl
lamp
%I”
ll@lCS
Intake
kr,h
sJpp11es
cables
(for
healer
2::
earchlng
5.0
3.0
1.95
1 se
2.4
-
200
” dc
equ1Fnent)
6
16
16
22
14
14
10
20
22
20
22
2u
22
P
22
22
10.7
0.57
0.97
0.34
28.5
0.G
14.5
i .o
l.Sj
1.59
4.33
0.51
0.34
17.3
23.3
11.3
4.3
: 8.0
0.5
d.5
0.5
/ .?
4.0
0.5
3.0
0.4
2.7
10.0
10.0
54.0
50.0
-___
TOTAL
:ng1ne
feed
ixnnps
(2.0
161)
lal"
tank
PUQXJ (2.0
&II
t1m
Lumps
(4.7
I&I)
WYenge
aas 1
'mans 3
BCUlJm
.T.s.
‘lndscree”
and No.7
Cm
mps
to.%
and 2 Iorwrd
(1416W)
rowdd
and Pear
om
W)
plrmp (46 WI
ruei
pnnp
020
w)
wiper
Plnnp (936 W)
Id4
10.0
10.0
23.5
12
12
4
13.5
13.5
22
4.6
7.1
1.5
023
1.6
4.7
6
5
11.5
4.8
1.7
5
9
2
%
2
2
TOTAL
381
163
163
88
5'4
23
19.2
3.4
10
18
%2
Table 4
WEIGHT OF INVERTORSTO SUPPLY 200 VOLT, THREE-PHASE, 400 Hz, AC
FROM 200 VOLT DC, AND INCREASE IN EQUIPMENTWEIGHT WHEN
USING DC TRANSFORMERS
AC invertors
Busbars
DC transformers
Total VA (Weight
required
lb
Number of
equipments
within
equipment
Total watts
required
Weight
increase
Maln 1
Main 2
1465
307
45
15
7
6
779
548
8.6
7.1
Main 3
Main 4
Essential
Essential
Essential
Essential
909
1190
871
250
500
240
33
40
33
11
22
11
8
12
8
6
4
5
770
9.5
749
880
231
640
223
12.1
9.4
4.3
5.1
3.8
TOTAL
59.9
1
2
3
4
TOTAL
210
Table 5
TOTAL WEIGHTSOF 200 VOLT AC AND DC SYSTEMS
200 V three-phase
Generating
Utilisation
Utilisation
ac
system
switchgear
cable
Weight
lb
1500
147
671
,
'
Generating
Utilisation
Utilisation
Invertors
200 V dc
Weight
lb
system
1113
switchgear
cable
for motors
Invertors for 200 V ac
Increased equipment weight
for dc transformers
TOTAL
2318
TOTAL
246
381
542
210
60
2552
‘I
i
41
Table
6
WEIGHT COMPARISON OF UTILISATION-CIRCUIT
PROTECTIVE
GEAR
USING FUSES WHERE POSSIBLE
DC system
AC system
Manual C.B.
3-phase
Fuse size 0
Fuse size 2
Fuse holder
111
0.33
250
51
25
0.011
0.066
0.11
36.6
2.75
3.35
2.75
Fuse
size
0
320
0.011
3.52
Fuse
Fuse
Fuse
10
size 2
size 3
holder
way
62
30
32
0.066
0.33
0.11
4.1
9.9
3.52
All
Table
manual
C.Bs.
(dc),
TOTAL
21
TOTAL
113
7
BREAKDOWN OF WEIGHT DIFFERENCES
Constant-speed
drives
Generators
(4 main + 1 emergency)
Control
gear and regulator
(including
C.S.D.
control
gear)
Switchgear
for generating
system
(including
contactors,
diodes,
fuses,switches)
26 V ac
Secondary
supplies
28 V dc
(invertors
and transformers)
200
v ac J
i
,Generator
system cabling
1Utilisation
switchgear
and protection
with:(A) manual C.Bs.
for both ac and dc systems
or (B) 3-phase
manual C.Bs.and
single-phase
and 200 V dc fuses
,Cable
in utilisation
circuits
1nvertors
for motors
IJeight
increase
in equipment
due to use of
dc transformers
Totals
Totals
L
DC system
lb
1
Item
with
with
A
B
+316
not
+16
>
+64
+120
r lot
requd.
+320
+210
+99
or
+25
+290
nlot requd.
nLot requd.
+942
+942
+542
+60
+1176
+1102
DC system
234 lb heavier
with
protective
gear
A.
DC system
160 lb
with
protective
gear
B.
heavier
requd.
+81
42
REFERENCES
1
Title,
Author
NO.
-.
I.A.
Mossop
Circuit
interruption
electrical
2
3
Report
I.A.
Mossop
The current
F.D.
Gill
dc arc
mm Hg.
R.A.E.
Report
The current
F.D.
Gill
dc arc
R.L.A.
McKenzie
Law
relationships
electrodes
EL 1477
(1952)
and voltage
R.A.E.
Report
Effect
of
silver
of
in
air
relationships
electrodes
a stable
at
of
a stable
in
air
at
EL 1483
altitude
in
200 V ac and
(1952)
on arc
length
dc systems.
R.A.E.
T.S.
altitudes.
copper
between
aircraft
mm Hg.
l-760
Sims
voltage
(1946)
and voltage
4-760
Mossop
at high
EL 1409
between
I.A.
R.F.
of hxgh
systems
R.A.E.
etc.
Technical
Proposals
for
protection
of
Report
main
69259
system
200 volt
(ARC 32238)
layout
(1969)
and control
dc aircraft
and
electrical
sys terns.
Unpublished
D.O.
Burns
Voltage
regulation
generators
Stickels
Artificial
Andrew
A design
use
R.A.E.
MAS paper
Technical
M.H.
Walshaw
Preliminary
T.R.
Andrew
a proposed
R.H.
Forrest
R.A.E.
P.A.
Stickels
of
dc circuit
breakers.
(1967)
switch,
for
dc supply.
Report
assessment
200 volt
Technical
excitation.
of a 10 amp thyristor
on a 200 volt
brushless
(1968).
MAS paper
study
speed
permanent-magnet
commutation
Unpublished
T.R.
(1967)
of variable
with
Unpublished
P.A.
MAS paper
68126
of
methods
dc aircraft
Report
(1968)
68106
of
switching
power
system.
(1968)
for
43
REFERENCES (Contd.)
-NO.
10
Title,
Author
D.E.
Marshall
Some notes
on the
for
conversion
use
in
availability
200 V dc aircraft
Unpublished
11
W.J.
Shilling
Exciter
equipment
MAS paper
in
of
power
transistors
operating
generating
armature
ments
etc.
from
a
system.
(1966)
reaction
a brushless
and excitation
require-
rotating-rectifier
aircraft
alternator.
12
Foust
Trans
AIEE 79,
Part
II,
394-402
Trans
AIEE 63,
page
198
(1944)
Trans
AIEE -63,
page
961
(1944)
Notes
on the
(1960)
Hutton
13
Cunningham
Davidson
14
T.D.
Mason
measurement
of
for
use in
unbalanced
Technical
Note
parameters
aircraft
alternator
resistive
load
studies.
R.A.E.
15
16
17
18
W.R.
Hinton
A theory
C.A.
Meadows
interference
L.C.
Caddy
R.A.E.
British
Standards
Institution
Nyvin
British
Standards
Institution
Minyvin
B.S.G.
195
British
Standards
Institution
Efglas
type
and ar.alysis
of
radio
Report
electric
66391
cables
(1966)
for
aircraft.
177
type
electric
electric
aircraft.
Klingshirn
Polyphase
H.E.
Jordan
non-sinusoidal
cables
cables
for
aircraft.
with
copper
conductor
,
192
E.A.
Trans.
design
(1961)
suppressors.
type
B.S.G.
19
the
Technical
B.S.G.
for
for
EL 199
induction-motor
I.E.E.E.
voltage
PPS87,
performance
sources.
624-631
(1968)
and
losses
on
44
REFERENCES(Contd.)
Further
to certain
include:-
papers are being prepared by the R.A.E.
aspects of equipment for the 200 volt
dc system,
(a) Some notes on the design and performance
dc generators.
(b)
ccm"erslOn
Some notes on the factors
equipment.
affecting
relating
in more detail
The subjects will
of medium-voltage
brushless
the design and weight
of power-
-
Legend
BTC
CB35
C825
@j
I.
Bus tie contactor
Manual cwcult-breaker
Manual cwcwt-breaker
Manual clrcwt-breaker
j5amp
Fjamp
I5 amp
cot
EBB
GCC
Change-over contactor
Essential busbar
Generator control cod&or
irjor
tco
rt-BTC
%
-
MBB
GCC
-MB0
MBB
C 035
x35
:e35
Unit
CCC
tDC
$
,
Mom busbar
Spld system contoctor
Tronsformtr
115/26voltac
Tronsformer-rectlfler
contactor
re;r-oy?fer-rectifuer
GCC
-
MBB
ssc.
T
Ice25
,
a
,
$
, Cl
C
$TRU
EmZqency
generator
Fig. I Typical 4 generator
1
I
*------welt
system, 200volt
150amp~~
a c, based on Concorde
EBB
Legend
D250
D35
EBB
FZOO
Diode 250 amp
Dlodo
35 amp
Essential
busbor
Fuse ZOOamp
F50
F25
F I5
GPC
-Fuse 50 amp
Fuse 25amp
Fuse I5 amp
Ground power contactor
MB0
OLC
T
TC
Mam busbar
Overload contactor
Transformer
200/28volts
Transformer
contactor
dc
‘MBB
sir
F200
ac
lnvertor
DJ5
[I TC
J
‘lo
F5“
F50
EL2”cg
I28
generator
Fig .2 Typical 4 generator
system 200volt
volt
150 amp
-b
d c , equivalent to Fig. I
I””
90
BO
70
0.01
Fig.3
L-----_
-_
-_
--_---.
0.02
Variation
WUJ
U’W 4J) ‘II0 uI’un’oY’I
in static
Invertor
2
weight
II.3
with
O-4
a.50.6 0-7a4-9I
power rating
2
f’ouur
(low
rating
4
1
-
5
bl89
0”
kVA
altitude,70°C
ambient)
_
Arc
than
sustalned
3 seconds
for
less
Arc
Fig. 4
Length
of sustained
dc
arcs
sustcnnod
vs altitude
Pnnted m England for HerMaJesty’s Statronery Office by the
Royal Arcraft Establrshment, Farnborough. DdS02109 K 4
for
more
DETACHABLE
ABSTRACT
629.13.06s
&9.13.0-G?
:
t For c~~paratiw
purposes.
a 200 volt
dc eyetam
roi- a large
modem
j cmmerclal
aimraft
has been deslmed
and Its wel&t
compared
with
tit
or a ConMntional
three-phase
ac systen.
TO obtain
necessary
deslm
j lnlomt,m,
st”dles
have
bee”
made or B 50 kW blushless
dc generator.
the
, problem
or cl,-c”lt
intemptlm.
cmversim
eqlllpnent
and bmshless
motws.
; The vulnexabllity
or the
syetem
due to the possibility
or sastained
ares
, durlng
rault
c,,ndltims
has also
been
exmlned.
i It
Is concl”ded
that
until
1 in the deslm
or emVersion
; ~111 not be liater
than
cmsldenble
equlpnent
thhe ac system.
ard
wel&t
reduction
Can be
brushless
motors,
the
achieved
de sy%em
(over)
CkRD
‘ARC
;J-
CP No.
11%
629.13.066
19P
629.13.0-R
; For caDpamt1ve
prposes.
a 2uo volt
de systen
r0r a lal-ge
mcdem
, cmenxal
airmart
has been designed
and its
weight
canpared
with
,oi
a conventional
tie-phase
ac system.
TO cbtaln
necessary
design
1 i,,fom,at,m,
studies
have
tie
or a 50 kW bmShless
dc genelator.
; problm
or clnxit
Interruption.
converslm
equlpnent
md
bmsbless
,The
mlnerablllty
or the system
due to the posslblllty
of sustained
, d,,rinB
ralt
condltlC%?
has also
been examined.
I
been
It
1s ccncl”ded
that
“ntll
11, the de&z,
or cam?rslm
wlU
not be lighter
than
ccnsidemble
eq”iFment
the ac System.
and
we&X
reductlw
can be
brushless
moton,
the
that
the
motws.
arcs
aehleved
dc system
(over)
:
,
,
/
i
i------1
----
-,---L-m-
i
!
----
----------
C.P. No. I 186
0
HER
Crown
MAJESTY’S
copyrzghghf
Pubbshcd
by
STATIONERY
1971
OFFICE
To be purchased
from
49 H,gh Holborn,
London
WC1 V 6HB
13a Castle Street, Edrnburgh
EH2 3AR
109 St Mary Street, Cardiff
CFI IIW
Brazennose
Street, Manchester
M60 BAS
JO I-a,rfax
Street, Bristol BSI 3DE
258 Broad Street, Bummgham
Bl ZHE
: SO ChlLhester
Street, Belfast BT1 4JY
or through
booksellers
C.P. No. 1186
SBN 11 470454 6