Introduction to Electrical substation

A substation is a facility which is used to step-up or step-down the voltage in the utility power lines, voltage will be stepped up if the power is transmitted through long-distance transmission lines and it will be stepped down when the power is to enter the local distribution line. In general, an electrical substation is a place which transmits electricity from one part of the production system to others.

Generation, transmission, and distribution of the electric power is done by the substation, substations are entities that integrate the power system

The design objective of a substation

The design objective of a substation is to provide maximum reliability, flexibility, and continuity of service. Substations provide transformation, switching, tie points, sectionalizing, protection and compensation

Equipment in a substation

Steel structures are used for towers of incoming and out-going transmission lines, towers are used to support strain insulators and flexible bus bars. In a substation, bus-bar is used to interconnect the loads and sources of electrical power. Incoming and outgoing transmission lines are connected by the bus-bar. It also connects the generator and main transformer in a power plant. Current carrying parts in a substation are supported by insulators it can provide mechanical support to the conductors and it is subjected to normal operating voltage and transient overvoltages.

Insulator selection must be properly done it must not fail due to mechanical load or overvoltages, it should have the ability to withstand the maximum wind loading, ice loading. Surge arrestors are connected between the phase and earth on the incoming side of the transmission line and it is also connected to the transformer terminal and earth. Surge arrestors are used in a power system to divert the lightning and switching overvoltage surges to earth without making any drop in residual voltage

What is the difference between switchyard and substation

Substation function is to transmit the electric power and according to the transmission requirements, it will step-up and step-down the voltage. Electrical power will be received by the incoming transmission lines and it delivers the electrical power through the out-going transmission lines

Switchyard delivers the generated power from the power plant at a required range of voltage to the nearest grid. 

Classification of sub-stations

Transmission substation

Its location is based on the transmission grid network and its transmission voltage level will be 420KV, 240Kv, and 145KV. The transmission voltage depends on the quantum of the power to be received and transmitted and the length of the transmission line. It usually connects transmission lines and it has many protection and control equipment

Distribution substations

The generated electric power must be distributed to the customers, due to the demand for power every customer needs electric power so the distribution substation is used to transfer the power from the transmission system and the distribution substation will step down the voltage and it divides the flow of electricity between the local outgoing lines of the local distribution network

Switching substation

Switching substation is a substation which doesn’t use transformers and it is operated in a single voltage level, it can be used as the collector and the distribution stations, it can also be used for switching the current to back-up lines and for circuit parallelizing in case of failures.

Transformer substations

In a substation, power transmission is done by stepping up or stepping down the voltage level of the electrical supply. So the voltage can be stepped up or down with the help of transformers hence it is called as transformer substation

Air-insulated substation

Air-insulated switchgear is used commonly for substations it provides flexibility in case of equipment configuration and it has low installation cost. Substations which use AIS can be found in transmission networks of all sizes.

Gas-insulated substation

In this type it uses gas-insulated switchgear it has all the functional element as the air-insulated type but it has an advantage of air-insulated type because it occupies one-tenth of the space of AIS type. This type can be used for harsh environments such as corrosive, salty air or extreme temperatures because of its reduced size it can be used in dense urban areas.


post-graduate in Electronics & communication.

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