The huge amount of power generated in a power station (hundreds of MW) is to be transported over a long distance (hundreds of kilo-meters) to load centers to cater power to consumers with the help of transmission line and transmission towers
The cost of conductor will be greatly reduced if power is transmitted at higher and higher transmission voltage. The use of higher voltage reduces voltage drop in the line resistance and reactance. Also transmission losses is reduced. Standard transmission voltages used are 132 kV or 220 kV or 400 kV or 765 kV depending upon how long the transmission lines are.
The magnitude of current decides the cost of copper, level of voltage decides the cost of insulators.. At different types of consumers.
Consumers may be
(1) big industries, such as steel plants,
(2) medium and small industries and
(3) offices and domestic consumers.
Electricity is purchased by different consumers at different voltage level. For example big industries may purchase power at 132 kV, medium and big industries purchase power at 33 kV or 11 kV and domestic consumers at rather low voltage of 230V, single phase. Thus we see that 400 kV transmission voltage is to be brought down to different voltage levels before finally delivering power to different consumers. To do this we require obviously step down transformers.
