Substation Components

Electric Substations are the part of the power system and used for transferring power from generating points to load centers. Some of the important components of substation are


Various incoming and outgoing circuits are connected to busbars. Busbars receive power from incoming circuits and deliver power to outgoing circuits.

Bus Bars
Bus Bars

Surge arrestors or Lightning arrester:

Surge Arresters or Lightning Arresters discharge the over voltage surges to earth and protect the equipment insulation from switching surges and lightning surges. Surge arresters are generally connected between phase conductor and ground. In a Substation surge arrester is located at the starting of the substation as seen from incoming transmission lines and is the first equipment of the substation. Surge arresters are also provided near the transformer terminals phase to ground. Two type of surge arresters are available 1) Gapped Arresters 2) Gapless Zinc – Oxide arresters.

Lightning Arrester or Surge Arreseter
Lightning Arrester or Surge Arreseter

Isolators or Disconnecting Switches:

Isolators are provided for isolation from live parts for the purpose of maintenance. Isolators are located at either side of the circuit breaker. Isolators are operated under no load. Isolator does not have any rating for current breaking or current making. Isolators are interlocked with circuit breakers

Types of Isolators are

  1. Central rotating, horizontal swing
  2. Centre-Break
  3. Vertical swing
  4. Pantograph type


Earth Switch:

Earth Switch is used to discharge the voltage on the circuit to the earth for safety. Earth switch is mounted on the frame of the isolators. Earth Switch is located for each incomer transmission line  and each side of the busbar section

Current Transformer:

Current transformers are used for Stepping down current for measurement, protection and control. Current transformers are of two types

  1. Protective CT 
  2. Measuring CT

Current Transformer
Current Transformer

Voltage Transformer:

Voltage transformers are used to step down the voltage for measurement, protection and control. Voltage transformers are of two types.

  1. Electro magnetic type
  2. Capacitive VT located on the feeder side of the Circuit Breaker.

Voltage Transformer
Voltage Transformer

Circuit Breaker:

Circuit Breaker is used for Switching during normal and abnormal operating conditions. It is used to interrupt the short circuit currents. It is used to interrupt short circuit currents. Circuit Breaker operations include.

  1. Closing
  2. Opening
  3. Auto – reclosing

Circuit Breaker is located near every switching point and also located at the both ends of every protection zone.

SF6 Circuit Breaker
SF6 Circuit Breaker

Power Transformers:

Power Transformers are used to step up or step – down a.c. voltages and to transfer electrical power from one voltage level to another. Tap changers are used for voltage control.

Power Transformer
Power Transformer

Shunt Reactors:

Shunt Reactors are used for long EHV transmission lines to control voltage during low – load period. Shunt reactors is also used to compensate shunt capacitance of transmission line during low load periods.  Usually Shunt reactors are unswitched.

Shunt Reactors Bank
Shunt Reactors Bank

Shunt Capacitance:

   Shunt capacitors are used for compensating reactive power of lagging power factor. Shunt Capacitors are used for improving the power factor. It is also used for voltage control during heavy lagging power factor loads. Shunt Capacitors are located at the receiving stations and distribution substations. Shunt Capacitors are switched in during heavy loads and switched – off during low loads.

Shunt Capacitor Bank
Shunt Capacitor Bank

Series Capacitor:

Series Capacitors are used for some long EHV a.c lines to improve power transferability. Capacitors are located at the sending end / receiving end of the lines. Series Capacitors are provided with by – pass circuit breaker and protective spark – gaps.

Series Capacitors
Series Capacitors

Series Reactors

Series reactors are used to limit short – circuit current and to limit current surges associated with fluctuating loads. Series reactors are located at the strategic locations such that the fault levels are reduced.

Series Reactors
Series Reactors

Lightning Protection:

Lightning protection is used to protect substation equipment from direct lightning strokes. Lightning Masts are located at the outdoor yard. Overhead Shielding wires are used to cover entire outdoor yard.

Lightning Masts
Lightning Masts

Isolated Phase Bus System:

Isolated Phase Bus System provides connection between Generator and the main Transformer. It carries very high currents.

Isolated Phase Bus Duct
Isolated Phase Bus Duct

Neutral Grounding Equipment:

Neutral Grounding Equipment are Resistors and reactors. They are used to limit the short circuit current during ground fault. They are connected between neutral point and ground.

neutral Grounding resistor
neutral Grounding resistor

Line Trap:

Line Trap consists of Inductive coil usually connected in the outdoor yard incoming line. Line traps are usually mounted above Capacitor Voltage Transformer (CVT) or on separate structure.

Wave Trap or Line Trap
Wave Trap or Line Trap


Used for Insulation purpose. Different types of insulators are porcelain, Glass, Epoxy.

Porcelain Insulators
Porcelain Insulators

Power Cables:

Power Cables are used to carry the power. They are single core and three core. Types of power cables are PVC insulated, XLPE insulated.

XLPE insulated Power Cable
XLPE insulated Power Cable

Control Cables:

Control Cables are for protection, control and measurement etc.. They are of low voltage and PVC insulated. Control Cables are Multi core and Shielded.

XLPE insulated Control Cables
XLPE insulated Control Cables

Station Earthing System:

Station Earthing System includes Earth Mat and Earth electrodes placed below ground level. These Earth Mat and Earth electrode is connected to the equipment structures, neutral points for the purpose of Equipment earthing  and neutral point earthing.

Function earthing system is to provide low resistance earthing for

  1. Discharging currents from the surge arresters, overhead shielding, earthing switches
  2. For equipment body earthing
  3. For safe touch potential and step potential in substation.

Earthing Mat
Earthing Mat

Metering, Control and Relay panels:

To house various measuring Instruments, control Instruments, Protective relays. They are located in air-conditioned building. Control Cables are laid between Switchyard equipment and these panels.

Metering and Control Panel
Metering and Control Panel

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Comments 90 comments

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nazren 5 years ago

thanks for the note...very usefull...but, what is the function of air breaker switch?

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muhammad qaiser 4 years ago

its very good information about substation


If 220 kv receiving station near by project,than what will the power fator to be consider for transformer sizing at distribution system.

is it ok if consider 0.85 pf instead of 0.8 pf.

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sudhakar 4 years ago

hi kiran,,,,i am sudhakar from odisha,,i am doing powerplant course in NPTI(DURGAPUR),,,,,Please add information about switchyard and their equipment in details...........i am waiting for ur answer,,,thanks 4 years ago

Fantastic work this is.

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sushant143 profile image

sushant143 3 years ago from India

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lakhan kumar patnaik 3 years ago

Dear mam,

Can u explain how to calculate the relay settings for protection?

Amit 3 years ago

I have some questions that - 1. suppose total power of a mega food park is 5100 Kilowatt and the total utilities is 1200 kilowatt, so what KV of Transformer will be used for it? Please give me the answer and the rules for it, my id is Thank You.

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Krishna chilakabattini 23 months ago

Dear Sir,

If we can use 50 hetz transformer at 100 hetz what is the problem. Please give me information with formula's.

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BRUNO 13 months ago

Hi Sir, what are the powers of H59 and H61 transformers and how are they installed?

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God bless you. 6 months ago

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