Visit to 400 kV substation

Created by

- NANDAN DESAI

Location : Hadala, Rajkot, Gujarat

Location : Hadala, Rajkot, Gujarat

ABOUT THE SUBSTATION

The substation at Hadala (Rajkot), Gujarat is a 400 kV distribution substation.

It receives power at 400 kV from Adani Thermal power plant via Varsana, from Mundra

TPP via Chorania (Limbdi) and via Jetpur and from Varsana SS.

It sends power at two voltage levels – 220 kV and 132 kV to Morbi, Nyara (Rajkot),

Tappar, Gondal etc.

The substation is connected as a ring system as

Chorania

(Limbdi)

Amreli

Jetpur

Hadala

(Rajkot)

(Continue… )

(cont.)

The substation is having two main bus and one transfer bus for both 400 kV side and

220 kV side.

There are in total 6 lines of 400 kV level, 8+ lines of 220 kV and some lines of 132 kV

level.

It’s a record that there has been no accidents in this substation since last 2000+ days.

Equipments in substation

Lightening arresters

Wave trap

Current Transformer (C.T.)

Potential Transformer (P.T.)

Line isolator with Earthing switch

SF6 Circuit breaker with starting

resistance

Bus isolator

3 phase reactor

(cont.)

Equipments in substation

Power transformers

Cables trench & tray

Fire fighting facility

LIGHTENING ARRESTER

The lightening arresters (L.A.) are used to ground

the high voltage impulse falling on line during

lightening.

L.A. of all the lines connected to a bus are

connected in parallel in order to ensure the proper

grounding of surge as well as to increase its life.

The L.A. core is made up of Zinc Oxide (ZnO2). It

acts as a non-linear resistance i.e. it offers a very

high resistance during normal conditions and offers

low resistance to the surge voltages.

A ring type structure is attached to L.A. in order to

reduce the corona effect.

WAVE TRAP

A wave trap is used on those transmission

lines which are equipped with PLCC (Power

Line Carrier Communication).

As the communication signal frequency is

much different from line frequency and also

the voltage level is too low, it is quite

necessary to separate the power signal and

communication signal.

This task is performed by a wave trap which

simply consists of L-C series and parallel

filters.

INSTRUMENT TRANFORMERS

The instrument transformers are:

1. Current Transformers (C.T.) – Used to

measure phase current.

2. Potential Transformers (P.T.) – Used to

measure phase to neutral voltage.

In this substation at some places CVT

(Capacitive Voltage Transformers) are

used which does function of PT as well as

assisting the Wave Trap.

C.T. P.T.

LINE/BUS ISOLATORS

Centre Break

Isolator

Double Break

Isolator

Pantograph type bus isolators

LINE/BUS ISOLATORS

The line isolators are used to isolate the line (after the operation of opening C.B.)

under maintenance from the healthy system which otherwise may get resulted in L-

G fault.

The bus isolators are used to isolate the bus under maintenance.

In this substation normally line isolators were centre break type isolators while the

bus isolators were either double break type OR pantograph type isolators.

The disc type structure at the tips of centre break type isolator is to reduce the

corona loss while they are open.

(cont.)

CIRCUIT BREAKERS

In this substation almost all the circuit

breakers are SF6 type circuit breakers.

There is a switchable series resistance along

with the C.B. as shown here. It is inserted

while closing the circuit breakers for a short

time.

This resistor, hence, limits the charging

current of the line’s stray capacitance.

3 PHASE REACTOR

The shunt reactors are used to absorb the excess of

reactive power in the transmission lines.

In this substation as long transmission lines are

terminating in, their stray capacitance inject reactive

power to absorb which, the reactor is installed here.

The installed reactor is capable to reduce the line

voltage by as much as 5 kV.

In this substation, power lines coming from wind

power station is also terminating. Since, there are

large variations in the power production, their reactive

power demand is also varying. Hence the reactor here

is a switchable reactor.

POWER TRANSFORMER

This substation has two type of power transformers:

1) 400 kV 220 kV and

2) 220 kV 132 kV

The cooling system employed is forced air – forced oil.

The cooling systems of transformers are automatically

controlled. Once the temperature reaches 70 C, the

cooling system starts and as temperature reaches 60 C,

the systems switches OFF.

The supply to the cooling system is given from the

substation supply transformer.

400 kV transformer

220 kV to 132 kV transformer

CABLES TRENCH & TRAY

The cables that collect the communication signals from

instrument transformers, circuit breakers, isolators,

wave traps etc. are made to run in cable trench

towards the control room.

The place where all the cables are collected is called

cable tray.

FIRE FIGHTING FACILITY

As oil is used as coolant and body insulator, there are possibilities of fire in case of

short circuits.

Fire fighting facility available in two ways in this substation.

One way is that at some particular distance gaseous fire extinguishing cylinders

are kept.

Another is that a water pipe runs everywhere in substation. In case of fire, it

sprinkles the water in surrounding area in fine molecular form in order to stop

propagation of fire.

CONTROL ROOM & RELAY ROOM

• The control room has various control panels which shows the information like

incoming power, outgoing power, frequency, time common to all substations, status

of various lines (healthy, faulted, under outage or maintenance), status of various

protective instruments like isolators, circuit breakers; temperatures of various

instruments, working tap of transformers etc.

• The DAS (Data Acquisition System) is used to accumulate the data received from

various sources.

• The relay room is separate from the control room. All relays used here are numerical

and are either from Siemens OR ABB .

• The protection system is so fast that it can detect a fault within 30 ms and hence the

circuit breaker can be operated within as less as 80 ms.

• For 400 kV side C.B., one time auto reclosure is allowed in order to clear the

temporary faults automatically.

Control Room Relay Room

BATTERY ROOM

The control panels and relays of the substation require DC supply of 220 V.

This DC supply is made with the help of battery bank reserve normally kept in a

separate room called Battery room.

The batteries used in this substation are Nickel-Cadmium (Ni-Cd) batteries. These

batteries are used due to their advantages like low maintenance, longer life (15-25

years) etc.

Each cell is of 2 V and 6Ah capacity.

The battery room and the battery chargers are shown in next slide.

BATTERY ROOM & ITS CHARGERS

Battery Room Battery Chargers