FIXING OF MAXIMUM DEMAND METERS:
1
To consider common requirements for 33KV switchgear and metering
2
To explain the fixing aspect of all various types of maximum demand meters.
INTRODUCTION: Practically maximum demand meters are of various sizes and ratings.
The meter reader/fixer who is to install any of the MD meters must have a good
and clear knowledge of how best to carry out the assignment. If he is in doubt, he
should not fumble but ask his superior officer of any information he may require to
carry out the installation correctly. He should not attempt to carry out the
installation. On trial and error bases as this is highly dangerous.
INFORMATION:
There are two types of maximum demand meters
(a)
Whole current maximum demand meter (W/C)
(b)
Standard board C/T operated maximum demand meters.
Any of these MD meters can be made used of in a consumer premises according to the
total load the consumer will require, for a load of – 20 – 45VA – a whole current maximum
demand meter is installed for a consumer.
For any load which is not more than 20KVA the consumer will require a whole current
(w/C) maximum demand (MD) meter of 25 amperes in size.
If the total load of the consumer is more than 20KVA but not more than 45KVA the
consumer will require a whole current of 50A in size. The moment the load is above
50KVA but not more than 75 KVA, it will be a standard board maximum demand meter C/T
operated that the consumer will require which will be 100/5A in size with current
transformer of the same rating as well. The standard boards MD meter are of various
sizes. In installing them. Current transformers are made use of tabulation regarding the
installation of standard board MD meters are as follows:
CONSUMERS’ LOAD
75KVA
120KVA
210KVA
320KVA
450KVA
STANDARD BOQRD MD METER SIZE
WITH C/T OF SAME RATINGS
100/5A
200/5A
300/5A
500/5A
800/5A
In installing various sizes of MD meters current transformers of equal sizes are made use
of. But there are some conditions when the load of a consumer is increased, instead of
changing, the meter. If the meter can still carry the load it is the current transformer that
is changed. This situation gives rise to multiplying factor.
See example as follows:
STANDARD BOARD M.D. METER:
100/5A
200/5A
500/5A
C/T’S
M/F
200/5A
300/5A
800/5A
2
3/2
8/5
The moment the load required by the consumer is more than 500KVA, it is H/T meter that
will be installed in the consumer’s premises.
HIGH TENSION
11KV
TRIVECTOR
100/5A
200/5A
400/5A
C/T
100/5A
200/5A
400/5A
The attached manual will throw a more light on the common requirements for 33KV
switchgear and metering installed in consumers’ premises.
1
GENERAL:
The following specification is for 33KV switchgear and metering installed in the customer’s
premises on behalf of the Authority. The equipment specified is to be ordered with and
will form part of the customers own 33KV switchboard.
2
SYSTEM DATA:
Rated Voltage
Highest system Voltage
Impulse level
Fault level
33KV
37KV
200KV
750MVA/1000MVA
Rated Frequency:
50HZ
Number of phases
3
Neutral effectively/non-effectively earthed (Delete which-ever nonapplicable)
3
METHOD OF SUPPLY:
Two methods of supply at 33KV to the customer’s premises are specified:
(a)
Radial supply as shown in figure No. 1
(B)
Ring supply as shown in figure No. 2
The method chosen will be determined by the Authority and will be governed by such
factors as:
4.
(a)
The location of the customer’s substation in relation to the Authority’s
networks.
(b)
The size of the customer’s load
(c)
The overall plans for the development of the 33KV system in the area.
33KV SWITCHGEAR:
4.1 RADIAL SUPPLY
The following 33KV equipment is to be provided on behalf of the Authority under
this arrangement:
(a)
One-33KV skeleton transformer – Feeder bay comprising one 3phase
33KV, 630 Amps Isolator with earthing blades connections of 630
Amps rating.
(b)
CURRENT TRANSFORMERS (METERING)
2 No. current transformers (ratio as specified)
............/5A . 15VA class B.M for main metering * 2 No current
Transformers as above for check metering and customer’s
exclusive use.
(c)
VOLTAGE TRANSFORMERS
1 No. 3 phased voltage transformer (ratio as specified)
.........../110V. 50VA per phase class B.
* 1 No. 3 phase voltage transformer as above for check
Metering and customer’s exclusive use.
(d)
METER
One trivector meter equipped with maximum demand indicator and
cumulative demand indicator on KVA section only, and cyclometer
registers on KWH, KVAH and KVARH sections. The trivector meter
shall be forwarded to the authority’s meter test station. Lagos with
the error curves of current transformers and voltage transformers for
calibration before being put into service.
* Where provided, the Authority would advise that the check meter be
identical with the main meter.
(e)
ACCESSORIES FOR MAIN METER
(i)
1 No. test terminal block
(ii)
3 No. “Pull Cap” type fuses in voltage supply circuit to the
meter with provision for sealing.
(iii)
A suitable leck with key shall be provided on the door of the
metering panel.
* Consumers apparatus (Metering equipment, alarms and remote
controls) shall not be connected to the Authority instrument
transformers and where such connection is made it shall be regard as
illegal and be disconnected forthwith, the Authority shall not be liable
for whatever damage is caused to the customer’s apparatus as a
result of such disconnection.
NOTE:
* Required if customer provides check-meter, the arrangement of the
feeder bay should allow where possible for future installation of a
33KV circuit breaker and busbars as shown in figure 1. Also space
should be provided, for future installation of another 33KV feeder bay.
4.2 RING SUPPLY:
Under this arrangement, the following 33KV equipment is to be provided by the
customer on behalf of the Authority:
(a)
Two 33KV skeleton feeder bays (i.e. space provided for future
automatic oil circuit breakers) each comprising one 33KV 3-phase, 800
Amps isolator with earthing blades, connections of 800 Amps rating.
(b)
33KV busbars of 800 Amp rating.
(c)
CURRENT TRANSFORMERS (METERING)
2 No. current transformers (ratio as specified)
......./5A 15VA class B.M for main metering
* 2 No. current transformers as above for check metering
and customer’s exclusive use.
(d)
VOLTAGE TRANSFORMERS
1 No. 3 phase voltage transformer (ratio as specified)
......./110V per phase class B.
* 1 No. 3 phase voltage transformer as above for check
Metering and customer’s exclusive use.
(e)
METER
One trivector meter equipped with maximum demand indicator and
Cumulative demand indicator on KVA section only, and cyclometer
Registers on KWH, KVAH and KVARH sections. The trivector meter
shall be forwarded to the Authority’s meter test station, Lagos with
the error curves of current transformers and voltage transformers for
calibration before being put into service.
*Where provided, the Authority would advise that the check-meter
Be identical with the main meter.
(f)
ACCESSORIES FOR MAIN METER
(i)
1 No. test terminal block
(ii)
3 No. “Pull Cap” type fuses in voltage supply circuit to the
meter with provision for sealing.
(iii)
A suitable leck with key shall be provided on the door of the
metering panel.
* Consumers apparatus (Metering equipment, alarms and remote
controls) shall not be connected to the Authority instrument
transformers and where such connection is made it shall be regard as
illegal and be disconnected forthwith, the Authority shall not be liable
for whatever damage is caused to the customer’s apparatus as a
result of such disconnection.
NOTE:
* Required if customer provides check-meter, space should be
provided for future installation of circuit breakers in feeder bays, See
figure No. 2.
4.3 OTHER TYPES OF SWITCHGEAR
In certain circumstances, the installation of 33KV indoor, metal clad or packaged
switchgear may be accepted if justified.
In such cases, the general arrangements of the PHCN’s portion of the indoor
substations mentioned in 4.1 and 4.2 above remain the same.
5.
STRUCTURES
Structural steel-work shall be not dipped galvanized. Galvanising shall be carried
out after cutting, punching drilling etc. It shall consist of a coating of at least 2 OZ.
of zine OER SQ.MM of surface and shall not be less than 08MM in thickness. The
zinc coating shall be uniform, adherent, clean, smooth, continuous and free from all
spangles and flux stains. The quality of galvanizing shall pass the tests prescribed
in B.S. 729 steel bolts and all necessary hardware shall comply with the B.S.S. for
structural steel. In addition to all dead and dynamic loads the structure shall be
designed to withstand a wind load of not less than 8 GM/SQ/CM all of the projected
area.
Minimum thickness of any galvanized section shall be 4.5MM at the ground surface
not less than 6MM.
6.
METERING AND INSTRUMENTS:
An outdoor pole mounted 33KV metering unit containing current and voltage
transformers of available is preferred, in which case an outdoor cubicle shall be
mounted on the 33KV substation site to house the following:
(a)
(b)
One 3-phase unbalanced load KWH – Meter and maximum demand (KVA)
indicator – trivector (about 600MM
x 500 “
x 220 “
One ammeter reading0, ........
(c)
One voltmeter reading – 40KV
The cubicle shall accommodate multicore cable and ant condensation hearting. The
cubicle shall be protected against corrosion either by galvanizing or painting
suitable for tropical climate. PHCN may supply and install the meter and
instruments (a) and (b) and (c) above during commissioning.
Alternatively indoor switchgear may be according to PHCN specification and
requirement.
7
WIRING:
In all cases, the sequence of the wiring terminals is to be such that the junction
between multicore cables and the terminals is effected without crossover. Claw
washes of an approved type are to be used to terminate all small wiring. Insulating
bushes are to be provided where necessary to prevent the chafing of wiring. All
secondary wiring is to be polyvinyl chloride (P.V.C) insulated and if multi-core, P.V.C
sheathed cable, or other fire resting cable of an approved type. All circuits are to
be wired in 600 volt grade cable. The conductors are to be of copper and have a
minimum cross section equivalent of 1.5 SQ.MM respectively.
Single core
conductors shall not be used.
All secondary wiring is to conform to the
requirements of B.S 2004 where applicable.
The following wire colours are to be used:RED
...
...
...
Red – phase connections in circuit current
and voltage transformer circuit only.
YELLOW
...
...
Yellow-phase connections in current and voltage
transformer circuit only.
BLUE ...
...
...
Blue-phase connections in circuit and voltage
transformer circuits only.
GREEN ..
...
...
neutral connections, whether earthed or unearthed and
insulated earth wires.
BLACK ...
...
...
Connections in A.C circuits other than current and
voltage transformer circuits.
Connection in A.C/D.C circuits.
GREY ...
...
...
Connection in D.C. circuits.
All wires are to be fitted with numbered ferrules of an approved type at each
termination. The numbers should comply with circuit function letter herewith
attached (schedule) E. At points of inter-connection between wiring, where a
change of numbering cannot be avoided, double ferrules are to be provided on
each end of the wires at the junction. Such points are to be clearly indicated on
the wiring diagram.
The ferrules on all wiring directly connected to circuit breaker trip coils tripping
switches, etc. are to be of a colour, preferable red different from that of the
remainder and marked ‘trip’ in addition to the numbering already specified.
No wires may be tied or joined between terminal points.
Electrical wiring and instruments are to be so located that leakage of water or oil cannot
affect them. All metallic cases of instruments, Meters Relays, etc. are to be connected by
means of bare copper conductors of not less than 2.5 SQMM cross section to the nearest
earth bar. All terminal boards are to be mounted in accessible position. The spacing of
adjacent terminal boards and their location above incoming cable gland should be such as
to allow ease of connection without undue bending of each core of the multi-core cable.
Separate studs are to be provided, on each terminal strip for the cores of incoming and
outgoing cables including all spare cores.
Brass bolts and studs are to be of not less than O.B.A. size. Stainless steel and bronze
down to 2 D.A may be used provided that the current carrying capacity is adequate. All
studs are to be provided with nuts, washes and lock nuts or lock washers, insulated
barriers are to be fitted between adjacent terminals and are to be fitted with non
inflammable transparent covers to prevent contact with any live parts. They are to have
warning labels with red lettering, mounted there on a conspicuous position.
All connections are to be made at the front of the terminal boards and no live metal is to
be exposed at the back. Screw terminations or pinch terminations are not to be used in
any section of the equipment unless especially approved by the Authority.
8
EARTHING:
The metal work of all equipment shall be connected to an appropriate substation earthing
system
Where any equipment includes metal work which may be handled by an operator whilst
the substation is alive such as ganged isolators, such metal work shall be connected to an
earth mat so situated as to include in its area the whole of the ground on which the
operator could normally stand. The earth mat should be of copper wire of section not less
than 35 SQ.MM and be in accordance with the B.S.S. 1320.
9.
EQUIPMENT CHARGEABLE TO PHCN
The Authority agree to purchase the following equipment from the customer, but reserve
the right to limit its financial commitments to an “Open Tender” value:
(a)
Incoming feeder or feeders as specified in 4.1 or 4.2 respectively
(b)
Voltage transformer with associated switchgear and metering.
(c)
Current transformers for metering
(d)
The metering unit cubicle and associated equipment as detailed in 6 above.
The cost of the switchgear chargeable to PHCN shall approved by commercial department,
PHCN headquarters before ordering.
10
ADDITIONAL EQUIPMENT FOR TOOLS
The following equipments shall be provided by the customer at the substation and shall be
made available for use by the Authority as and when required:
11
(a)
Earthing equipment for the switchboard if not integrals;
(b)
Operating and servicing tools, and manufacturers manuals;
(c)
A reasonable stock of spare parts for the switchgear.
DETAILS TO BE SUBMITTED TO PHCN
The manufacturer’s specification together with general arrangement and schematic
drawings is to be submitted to the Assistant General Manager (Commercial), PHCN
Headquarters, P.M.B 12030, Lagos, for approval before a firm order is placed. Six copies
each of the general arrangement, wiring and foundation drawings are to be supplied
within six weeks of confirmation of the order. Duplicate copies of test sheets for metering
C.T’s and V.T., showing the ratio and phase-angle errors at different burdens are to be
supplied before shipment of the switchboard.
One copy of the manufacturer’s
maintenance manual and operating instructions shall be submitted to the Assistant
General Manager (Commercial) for all equipments chargeable to the Authority. All
correspondence and drawings in connection with this specifications must be in the English
Language.
SCHEDULE E.
CIRCUIT FUNCTION LETTERS
a)
Current transformers for primary
protection, excluding over current
WIRE NUMBERS
10-29 Red phase
b)
Current transformers for bus bars
protection
30-49 Yellow phase
50-69 Blue phase
70-89 Residual circuits and neutral
Current transformers
c)
Current transformers for overcurrent
current protection (including)
combined earth-fault protection
And instruments
90
d)
Current transformers for metering
and voltage control
91-99 Test windings normally
inoperative
e)
Reference voltage for instruments
Metering and protection.
f)
Reference voltage for voltage control
g)
Reference voltage for synchronizing
h)
A.C. and A.C/D.C supplies
i)
D.C. supplies
j)
Closing and tripping control circuits
k)
Alarms and indicators initiated by
auxiliary switches and relay contacts
excluding those for general indicator
equipment.
l)
Auxiliary and control motor devices e.g. Governor
motor, rheostat motor generator AVR control:
Spring charging motors, transformer cooler motors,
control, motors for isolater operation.
Earth wires directly
connected to the
earth bar.
1-69 Switchgear and Generators
70-99 Transformers
Any number from 1 upwards
1-19 Switchgear
20-69 Generators
70-99 Transformers
m)
Tap change control, including ARC,
Tap position and progress indications.
n)
An indication that the forruling is not in
accordance with the general scheme and
that if it is not altered double ferruling
will be required for co-ordination with the
Remaining equipment in the station (See rule 9)
o)
D.C tripping circuits used solely for bus bar
Protection.
p)
Interlock circuits not covered above.
q)
D.C. instruments and relays, exciter and field
circuits for generators.
r)
Pilot conductors (including directly
associated connections) between panels
independent of the distance between them
for pilot-wire protection, for intertripping
or for both.
s)
Connections to and from light
current control equipment.
t)
Alarms and indications to and from
general indication and remote selective
control equipments
u)
Telephones.
Any number from
1 upwards.
Spare cores shall be numbered from
1 upwards in each cable and shall
be so arranged that they can be
readily identified on site with the
Cable containing them. This shall
be achieved by suitable grouping
and unless the location of each
group is clear from the diagram, the
groups shall be labeled.
Alternatively, the core number shall
be preceded by the cable number.
Any number from 1 upwards
If, for functions A-G and for function H, J, and m, more number are required, any
multiples of one hundred e.g. 10-29 may be extended to 110-129 etc.
Note: The term “remote selective control” denotes “control at a point distant from the
switchgear by the transmission of electrical signals through common communication
channels using selective means to operate one of a number of switching devices.”
COMMERCIAL DEPARTMENT.