SUBSTATION- Introduction, Components and Types

SUBSTATION- Introduction, Components and Types


A substation is basically an assembly of apparatus or equipment which are installed to control the transmission and distribution of electric power. There are numbers of substations, which are installed in power system to handle the electric power before it is being delivered to the consumers. Substations is used in electric power system for the following functions:

1. Voltage Level Transformation

Transformers are the heart of substation. The main function of substation is to step up or step down the voltage according to the requirement of power system.

2. Switching Operation

The another very important function of substations is switching operation. Substation are used to switch ON and OFF the power lines.

3. Power Factor Correction

Power factor is a ratio of true power over apparent power. Substation improves the power factor of electric system by installing bank of static capacitors at the receiving end of the line.

4. Power Converting Operation

Power converting operation means to convert the AC supply into DC supply or vice versa. The substations which perform this power converting operation is known as Converting Substation.

5. Frequency Correction Operation

Substation also perform the frequency correction operation. Substation convert frequency from higher to lower or lower to higher according to the requirement of power system.


The substation consist of many components but there are some components or equipment which are common in all types of substations. The size of these components may vary according to the type and size of substation. The main components of substation are:

  • Transformer
  • Circuit Breaker
  • Isolator
  • Insulator
  • Capacitor Bank
  • Lightning Arrestor
  • Metering Equipment

1. Transformer

Transformer is a static machine which is used to transfer power from one circuit to another circuit at different voltage level, without changing its frequency. Transformer is a heart of substation. In substation, Step up or Step down transformer are used according to the requirement. Mostly, Step down transformers are used in substations. The step up transformer is used only in the substation which is near the generating station.


2. Circuit Breaker

Circuit breaker is basically an electrical switch which can works at both no load, full load or fault conditions. It protect the equipment from over load and Short circuit faults. When circuit breaker operate at ON load, Arc is produced between fixed and moving contact. To extinguish this arc, Arc quenching mechanism is used in circuit breaker. Based on the arc quenching medium, Circuit breaker are divided into different types like Air Circuit Breaker, Oil Circuit Breaker, Vacuum Circuit Breaker, SF6 Circuit Breaker etc.

Circuit Breakers

3. Isolator

Isolator is also an electric switch but it works only at NO load. Isolator open and closes the contacts only under no load conditions. Like Circuit breaker, It does not have any arc quenching mechanism. It is used for switching purpose under normal condition. The main purpose of isolator is to isolate the one section of circuit from another.

4. Insulator

Insulator are used to prevent the flow of current to earth through the line conductors. This is achieved by placing insulators between line conductors and supports. Insulator has a high resistive path which opposes the flow of current. Insulator has high mechanical and dielectric strength. There are various types of insulators but in substations mostly Suspension and Strain insulators are employed. 

Suspension Type Insulator

5. Capacitor Bank

Capacitor Bank is used in power system to improve the power factor. The power factor can be improved by connecting capacitors in parallel with the load which is operating at lagging power factor. The capacitors draws leading current which neutralize the lagging reactive component of original load current, Thus improves the overall power factor.

6. Lightning Arrestor

Lightning arrestor is a device which provides easy conducting path for the flow of current when the system voltage is more than designed value and acts as insulator when the system voltage is at normal level. Lightning arrestors protect system equipment from the high transient voltage which is produced in the system due to striking of lightning on the line. The lightning arrestor are placed as near as possible to the equipment to be protected against overvoltage. If the lightning arrestor is installed to protect the transformer, it is placed on the terminals of the transformer.

Thyrite Lightning Arrestor

7. Metering Equipment

Current transformer and Potential transformer are used in substation as metering equipment. Current transformer is basically an Step up transformer which is used with ammeter to measure the current of electrical power line. On the other hand, Potential transformer is step down transformer which is used with voltmeter to measure the voltage of line.


There are various types of substation available in electrical power system. Based on design, Substation are divided into two type:

  • Indoor Substation
  • Outdoor Substation

1. Indoor Substation

In indoor substation, all the apparatus are installed inside the substation building. This is the reason why these substation are called indoor substation. Indoor substation basically designed for 11kV but can also extended up to 33kV if the surrounding atmosphere is contaminated with impurities which may damage the substation equipment. These substation are installed where continuity of electrical supply is very important such as Hospitals, Industries, Education Institute, Cinema Halls and others commercial complexes etc.

Key Diagram of Substation

2. Outdoor Substation

The substations in which the apparatus are installed in the open yard are called outdoor substation. Outdoor substation can designed to handle any level of voltage. Unlike Indoor substation, Outdoor substation are not limited up to 33kV voltage level. Based on installation, Outdoor substation are also divided into two types:

  • Foundation Mounted Substation
  • Pole Mounted Substation

1. Foundation Mounted Substation

In foundation mounted substation as the name suggests, Transformer and all others apparatus are mounted on a foundation above the ground level. These substation are designed to handle power at 33kV or above. The primary and secondary transmission of electric power is handled by these substation.

Pole Mounted Substation

2. Pole Mounted Substation

In pole mounted substation, The transformer and others apparatus are installed on the pole structure. RCC poles are used to creating a suitable pole structure. The H-pole or 4-pole configuration are used to create the pole structure. The pole mounted substation receives power at 11kV and delivers it at 400/230 V. These substation are basically an distribution substations in which 3-phase, 11kV/400V step down distribution transformer is used. Pole mounted substation are erected at important places in various localities of a city.

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