Sub-station plays an important role in the electric power system. The continuity of the electric power supply depends on the successful operation of the sub-station. Sub-station may be a central location where the electric power is supplied from the powerhouse and this electric power is supplied through a network of transmission & distribution lines. Therefore it’s essential to require care of while designing and building sub-station.
There are few points which should be kept in consideration while laying out a sub-station.
It should be located at a correct site, as far as possible; it should be located at the middle of gravity of the load.
It should provide a secure and reliable supply to the consumers. Also for reliability purposes, it should be designed and constructed in a proper manner.
It should be operated and maintained easily.
It should be built on economic costs.
Classification of sub-station
Service requirement
Transformer sub-stations: Those sub-stations which change the voltage level of the incoming voltage and delivers at another voltage level to the consumers.
Switching sub-stations: These sub-stations don’t change the voltage level of incoming and outgoing lines. Simply they perform the switching operation of the facility lines.
Power factor correction sub-station: That sub-station which improves the facility factor level of the system is named the power factor correction sub-station. These sub-stations generally uses synchronous condenser because of the power factor improvement equipment.
Frequency changer sub-stations: Those sub-stations which change the availability frequency are referred to as frequency changer sub-station. Such frequencies could also be required for industrial utilization.
Converting sub-stations: Those sub-stations which convert the Ac quantity to Dc quantity are called converting sub-stations. These sub-stations receive power as an Ac quantity then they convert it to Dc with the assistance of rectifiers.
Industrial sub-stations: Those sub-stations which give electric power to the individual industries are called industrial sub-stations.
According to constructional features, sub-stations have many components like circuit breakers, switches, fuses, instruments, etc. which must be arranged in a proper manner to make sure the reliable service. Construction-wise they’re classified as:
Indoor sub-station: These sorts of sub-stations are installed for 11kv voltage thanks to economic consideration. They are often “> this is often built under the shades thanks to the contaminated atmosphere; these sub-stations can be erected for voltage up to 66kv.
Transformer sub-station :
Most of the facility system care with the voltage level changing which may be referred to as transformer sub-station because the transformer is that the main component to vary the voltage level, transformer sub-station are often classified into,
a) intensify sub-station b) Primary sub-station
c) Secondary sub-station d) Distribution sub-station
In the following diagram a typical electrical supply system showing the position of the above sorts of sub-stations.
Step up sub-station: this type of sub-station intensifies the generating voltage (11kv) to high voltage (220kv) to affect the economy of the electrical power grid. this is often known to intensify sub-station, which is usually located within the powerhouses.
Primary sub-station: The 220 kV is transmitted through a 3 phase 3 wire overhead system from step sub-station to the load center. the facility is then received by the first grid sub-station which reduces the voltage level to 66kv for secondary transmission.
Secondary sub-station: the electrical power of 66kv from the primary grid station is transmitted at a 3 phase 3 wire system to varied secondary sub-stations located at different positions. At the secondary sub-station, the voltage level is reduced to 11kv, which transmission lines line the roadside.
Distribution sub-station: These sorts of sub-stations receives 11kv power from the secondary sub-stations and located near the localities of consumers. Here the voltage is stepped right down to 400v, 3 phase 3 wires for the consumers. The voltage b/w two phases are 400v while b/w single phase and neutral is 220v.