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SWITCHYARD
Switchyard means collection of electrical equipment where high voltage electricity is
switched using of various component. Electrical switchyards are usually part of a substation
where electricity is transformed from one voltage to another for the transmission, distribution.
Or we can say that a switchyard is essentially a hub for electrical power sources. For instance, a
switchyard will exist at a generating station to coordinate the exchange of power between the
generators and the transmission lines in the area. A switchyard will also exist when high voltage
lines
need
to
be
converted
to
lower
voltage
for
distribution
to
consumers.
Therefore a switchyard will contain; current carrying conductors, grounding wires and switches,
transformers, disconnects, remotely controlled arc snuffing breakers, metering devices, etc.
A CGPL 400 kV switchyard is designed to evacuation of power generated at the plant. The
contract is a turnkey contract and is allotted to Siemens. The contractor will do all the detailed
engineering, procurement, testing etc itself and after total completion the Switchyard will be
handed over to CGPL.
The switchyard is designed based on the following codes and standards:
a)
IS-10118, Part-3: Code of practice for selection installation and maintenance of
switchgear and control gear.
b)
Central Board for Irrigation & Power (CBIP) - Technical Manual on Layout of
Substations
c)
Indian Electricity Rules
d)
Indian Electricity Grid Code
The 400 kV system is designed to withstand the lightning impulse voltage of 1425 kV
(peak),switching impulse voltage of 1050 kV (peak) and power frequency over voltage of 630
1
kV (rms). However, the lightning impulse voltage for line/bus reactor windings is 1300 kV
(peak).The lighting impulse withstand voltage for the outgoing lines is 1550 kV (peak)
The main buses are to carry continuous current of 4000A duly taking into account the designed
ambient conditions, effect of emissivity, solar radiation, proximity & skin effect, etc. Bay buses
are rated for 2500A. The main bus bars for 400 kV switchyard and connections between
equipments are tubular aluminum conductors according to standard matricides iron pipe size
(IPS) of suitable size. The Jack Buses are Quad bundle ACSR Moose Conductors and the
Outgoing lines are Triple Bundle ACSS Snowbird Conductors. The switchyard is designed for a
fault level of 50 kA for 1 sec. and dynamic rating of 125 Ka
A creep age distance of 31 mm/kV is provided for all switchyard equipment.
One and half Breaker Scheme is applied in the Switchyard.
The minimum clearance of Phase to Phase is 4000 mm, Phase to Earth is 3500 mm, Sectional
Clearance is 6500 mm and minimum Ground Clearance is 8000 mm.
The Corona Excitation Voltage is 320 kV ( rms)
The Radio Interference voltage at 266kV (rms) is <= 500 micro volts.
1 min P.F. withstand voltage is 630 kV ( rms)
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The 400 kV switchyard consist of following circuits :
Sl. No.
Description
No. of Circuits
1
Generator Transformer
5
2
Line with Shunt Reactor
4
3
Line without Shunt Reactor
2
4
Bus Reactor
1
5
Bus PT
2
6
Total
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The switchyard is supplied and installed with all equipment/systems and accessories to
make
the switchyard complete in all respects. The switchyard include all the equipment/systems
indicated below but not limited to the following.

400 KV switchyard equipment (circuit breakers, isolators with & without earth switches,
current transformers, capacitor voltage transformers, electromagnetic voltage transformers,
lightning arresters, wave traps, bus bars, insulators & hardware, clamps, connectors &
spacers, bay marshalling boxes, marshalling/junction boxes, etc.)

Power line signaling and communication equipment based on PLCC (Power Line Carrier
Communication)system

Line and bus reactors

SCADA (Supervisory Control and Data Acquisition) system for entire switchyard with bay
control units for each bay including event logging

Protection panels for all bays/equipment, communication and interfacing panels as required

Stand alone disturbance recorders with associated network cabling, PC, HMI, Printer and
evaluation software

ABT (Availability Based Tariff) meters including necessary software & hardware for
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monitoring on dedicated PCs with suitable networking

11kV/433V dry type service transformers and 415 V AC Distribution Board and associated
bus duct

415 V Emergency ACDB and Lighting Distribution Board

220V DC system for protection & control, 48V DC system for communication equipment
and UPS system for SCADA (including batteries, chargers, inverters, distribution boards,
etc.)

Earthing and direct stroke lightning protection system for switchyard and switchyard
control building

Lighting system for switchyard and switchyard control building

Cabling system for switchyard and control building (including all power, control &
instrumentation cables, cable carrier system, etc.)

Gateway interface for transfer of data to SLDC (State Load Dispatch Centre) and RLDC
(Remote Load Dispatch Centre)

Outdoor kiosks housing BCUs, protection panels, fault disturbance recorders, etc.

Air conditioning and ventilation system for control building and outdoor kiosks

Fire alarm and detection system

Fire protection system for switchyard and reactors
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LAYOUT
ACSR bundled stranded conductor will be
used for the connection between the
generator transformer gantries and incoming gantries in the switchyard. Minimum clearance of
10 m will be provided considering movement of crane/truck etc.
The switchyard will be provided with access ways near the current transformers and circuit
breakers and isolators/earth switches.
The cable trenches for the equipment will be run as close to their foundations as possible even
preferably touching.
The switchyard will be enclosed in fence around for safety and to prohibit unauthorized persons
from entering. Lockable gates for personnel entry and equipment will be provided at
convenient locations. The fence provided around switchyard will be of 3000 mm height and at
a minimum distance such that section clearance is available from any live part. The fence will
be suitably earthed as per relevant standards.
The soak pit and burnt oil pit for the line and bus reactors will be sized as per norms indicated
in CBIP Manual for Fire Protection of Power Transformers. The height of the fire barrier wall
for the reactor will be minimum 600 mm more than the height of the bushing.
Earth mat of suitable size with closely spaced earth conductor will be provided below the
operating handle of individual switchyard equipment.
Roads will be provided along the periphery of the switchyard within the fence and all
intermediate roads will be interconnected with the road.
The line gantries will be designed considering the take off location as 150 m from the
switchyard gantry.
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