An electrical power system consists of generation, transmission, and distribution. The transmission system supply bulk power and the distribution systems transfer electric power to the ultimate consumers.
The generation of electric energy is nothing but the conversion of one form of energy into electrical energy. Electrical energy is generated in hydro, thermal and nuclear power stations. Sometimes, electrical energy is generated from non-renewable energy resources like wind, waves, fossil fuels, etc. The generating voltages are usually 6.6kV , 10.5 kV, 11kV, 13.8kV, 15.75kV , etc.
Fig 1. Structure of power system
Components of an Electric Power System
> Generators – A device used to convert one form of energy into electrical energy.
> Transformer – Transfer power or energy from one circuit to other without change of frequency. (To increase or decrease voltage level)
> Transmission lines – Transfer power from one location to another.
> Control equipments – Used for protection purpose.
Primary transmission : 110kV,132kV or 220kV or 400kV or 765kV, high voltage transmission, 3𝜙 wire system.
Secondary transmission : 3𝜙,3 wire system, 33kV or 66kV feeders are used.
Primary distribution : 3𝜙,3 wire system, 11kV or 6.6kV,3𝜙,3 wire system.
Secondary distribution : 400 V for 3𝜙,230 V for 1𝜙.
Fig.1 shows the typical layout of a structure of power system. This network may be divided into transmission and distribution system.
Transmission system
It supplies only large blocks of power to bulk power station or very big consumers. It interconnects the neighbouring generating stations into a power pool. i.e., interconnection of two or more generating stations. Tolerance of transmission line voltage is ±5 to ±10% due to variation of loads.
The transmission system can be divided into primary transmission and secondary transmission.
Primary Transmission
If the generated power is transmitted through transmission line without stepping up the generated voltage, the line current and power loss would be very high. So, the generated voltage is stepped up to a higher value by using step up transformer located in substations known as sending end substations near the generating stations. The high voltage transmission lines transmit power from the sending end substation to the receiving end substation. Primary transmission voltages are 110kV ,132kV or 220kV or 400kV or 765kV. It uses 3𝜙,3 wire system.
Secondary Transmission
At the receiving end substation, the voltage is stepped down to a value of 66 or 33 or 22kV using step down transformers. The secondary transmission forms the link between the receiving end substation and the secondary substation. It uses 3𝜙,3 wire system and the conductors used are called as feeders.
Distribution System
The component of an electrical power system connecting all the consumers in an area to the bulk power sources or transmission lines is called a distribution system. A distribution station distributes the power to domestic, commercial and relatively small consumers. Distribution transformers are normally installed on poles or on plinth mounted or near the consumers. It can be divided into primary and secondary distribution system.
Primary Distribution
At the secondary substations, the voltage is stepped down to 11kV or 6.6kV using step down transformers. The primary distributor forms the link between secondary substation and distribution substation and the power is fed into the primary distribution system. It uses 3𝜙,3 wire system.
Secondary Distribution
At the distribution substation, the voltage is stepped down to 400 V (for 3𝜙 ) or 230 V (for 1𝜙) using step down transformers. The distribution lines are drawn along the roads and service connections to the consumers are tapped off from the distributors. It uses 3𝜙, 4 wire system. Single phase loads are connected between one phase wire and one neutral wire.
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