The conveyance of electric power from power station to consumers premises is known as electric supply system.
An electric consist of three principal components biz., the power station, transmission line and distribution system. Electric power produced at power stations which are located at the favorable places, generally quite away from consumers. It is then transmitted over large distances to the load centres with the help of conductor known as transmission line, it is distributed to a large no of small and big consumers through a distribution network.
The electric supply systems can be broadly classified into (1)d.c. or a.c. system
(2).Overhead or underground system.
Now a days, 3 phase, 3 wire and a.c. system is universally adopted for generations and transmission of electric power as an economical proposition. However, distribution of electric power is done by 3-phase, 4-wire and a.c. system. The underground system is more expensive than the overhead system. Therefore, in our country, overhead system is mostly adopted for transmission and distribution of electric power.
Typical a.c. Power supply scheme
The large network of conductors between the power station and the consumer can be broadly divided into two parts viz., transmission systems and distribution system. Each part can be further subdivided into two primary transmission and and secondary transmission and primary distribution and secondary distribution. Shows the layout of a typical a.c. Power supply scheme by a single line diagram. It may be noted that it is not necessary that all power scheme includes all the stages shown in the figure. For example, in a certain power scheme, there may be no secondary transmission and another case, the scheme may be so small that there is only distribution and the no transmission.
(1). Generating station :Generating station represents the generating ststion where electric power is produced by 3 - phase alternators operating in parallel. The usual generation voltage is 11kV. For the economy in the transmission of electric power, the generation voltage (i.e., 11kV) is stepped upto 132 kV or more at the generating station with the help of 3-phase transformers. The transmission of electrical power at high voltages has several advantages including the Saving the conductor material and high transmission efficiency. It may appear advisable to use the highest possible voltage for transmission of electrical power to save conductor material and have other advantages. But there is limit to which this voltage can be increased. It is because increase in transmission voltage introduces insulation problem as well as cost of a switch gear and transformer equipment is increased. Therefore, the choice of proper transmission voltage is essentially a Question of economics. Generally the primary transmission is carried at 66kV,132kV,220kV or 400kV.
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