Types of Substation
October 24, 2011
Generally the substations may be categorized based on their end applications i.e. if their purpose is to aid transmission of electric power or if it is for the distribution of electric power etc. On this regard a substation may categorized into the following:
Transmission Substation:
The three phase power from the generating station leaves to a substation where its voltage is stepped up to extra high voltage level for the purpose of transmission. Typical transmission voltages are 110kV, 220kV, 400kV and 765kV levels. Transmission substations frequently have two or more large power transformers. The transmission substations are for the purpose of stepping up the voltage level from 11kV to suitable transmission voltage depending upon the distance it to be transmitted.
Distribution Substation:
The transmission lines end at distribution substation, where power is transferred from the transmission system to the distribution. The voltage level is reduced to primary distribution voltage for residential, farm and industrial loads. A special class of distribution substation would include a dedicated customer substation. This is very much a normal distribution substation, but its capacity would be reserved only for the specific customer. The secondary voltage level of this type of substations may vary according to the customers requirement.
Switching Substations:
A Switching Substation does not house a power transformer as its operation is only of one voltage level. As the name would indicate, the purpose of this substation is to switch the power back to the transmission lines in case of any failure or for the purpose of paralleling.
The power system network is such designed that, any faults that possibly occur with in the system would result only in a minimum interruption of services. Failure of components or part of the system, would cause other components or parts to carry more power than they normally do. Hence, while evaluating the substation design, it is necessary to be aware of the configuration of the system to which the substation is going to a part of. Based on this, the types of bus configurations followed are as follows:
Single Main Bus:
In this configuration, the system has only one main bus which is energized and all the circuits are branched form the bus. This is the most simplest configuration but it is not reliable.
Sectionalized Bus:
Two or more Single Bus schemes connected together with a breaker forms the Sectionalized Bus scheme. The sectionalizing breakers shall be kept normally open or normally closed, depending upon the requirements. The part of the system which has failed can be safely isolated and hence eliminating the need of total shutdown of the substation unlike the Single Bus scheme.
Main Bus and Transfer Bus:
In this scheme there are two buses, one main bus and a transfer bus. The main bus is normally energized at all times and all the incoming and outgoing circuits are connected to the main bus through their associated circuit breaker and switches. In case of any requirement to isolate any part for maintenance purpose or because of any faults, the integrity of the circuit operation can be maintained with the help of the bypass equipment.
Ring Bus:
This arrangement is an extension of one or more Single Bus scheme with an circuit breaker to interconnect both the open ends. In this fashion, a closed ring is formed with a circuit breaker connecting each section.
One and Half Circuit Breaker Scheme:
This configuration has two main buses, both normally energized. In this arrangement three circuit breakers are used for two independent buses, hence forth each bus sharing one and half circuit breaker. This scheme has the advantage of removing any circuit breaker with out interrupting any circuit. Also, faults on any either of the main buses caused no circuit interruptions.
Apart from this, the substations can also be categorized as Air Insulated Substations(AIS) and Gas Insulated Substations.(GIS) The AIS are constructed outdoor and requires more of land area. The GIS are compact, indoor substations. They need lesser land area because the equipments are enclosed together as a panel with its connections made internally and terminals left outside.
Transmission Substation:
The three phase power from the generating station leaves to a substation where its voltage is stepped up to extra high voltage level for the purpose of transmission. Typical transmission voltages are 110kV, 220kV, 400kV and 765kV levels. Transmission substations frequently have two or more large power transformers. The transmission substations are for the purpose of stepping up the voltage level from 11kV to suitable transmission voltage depending upon the distance it to be transmitted.
Distribution Substation:
The transmission lines end at distribution substation, where power is transferred from the transmission system to the distribution. The voltage level is reduced to primary distribution voltage for residential, farm and industrial loads. A special class of distribution substation would include a dedicated customer substation. This is very much a normal distribution substation, but its capacity would be reserved only for the specific customer. The secondary voltage level of this type of substations may vary according to the customers requirement.
Switching Substations:
A Switching Substation does not house a power transformer as its operation is only of one voltage level. As the name would indicate, the purpose of this substation is to switch the power back to the transmission lines in case of any failure or for the purpose of paralleling.
The power system network is such designed that, any faults that possibly occur with in the system would result only in a minimum interruption of services. Failure of components or part of the system, would cause other components or parts to carry more power than they normally do. Hence, while evaluating the substation design, it is necessary to be aware of the configuration of the system to which the substation is going to a part of. Based on this, the types of bus configurations followed are as follows:
Single Main Bus:
In this configuration, the system has only one main bus which is energized and all the circuits are branched form the bus. This is the most simplest configuration but it is not reliable.
Sectionalized Bus:
Two or more Single Bus schemes connected together with a breaker forms the Sectionalized Bus scheme. The sectionalizing breakers shall be kept normally open or normally closed, depending upon the requirements. The part of the system which has failed can be safely isolated and hence eliminating the need of total shutdown of the substation unlike the Single Bus scheme.
Main Bus and Transfer Bus:
In this scheme there are two buses, one main bus and a transfer bus. The main bus is normally energized at all times and all the incoming and outgoing circuits are connected to the main bus through their associated circuit breaker and switches. In case of any requirement to isolate any part for maintenance purpose or because of any faults, the integrity of the circuit operation can be maintained with the help of the bypass equipment.
Ring Bus:
This arrangement is an extension of one or more Single Bus scheme with an circuit breaker to interconnect both the open ends. In this fashion, a closed ring is formed with a circuit breaker connecting each section.
One and Half Circuit Breaker Scheme:
This configuration has two main buses, both normally energized. In this arrangement three circuit breakers are used for two independent buses, hence forth each bus sharing one and half circuit breaker. This scheme has the advantage of removing any circuit breaker with out interrupting any circuit. Also, faults on any either of the main buses caused no circuit interruptions.
Apart from this, the substations can also be categorized as Air Insulated Substations(AIS) and Gas Insulated Substations.(GIS) The AIS are constructed outdoor and requires more of land area. The GIS are compact, indoor substations. They need lesser land area because the equipments are enclosed together as a panel with its connections made internally and terminals left outside.
Posted by Anup Mohan. Posted In : Electrical Substation
