The delivery of electrical energy in huge bulk from the
generating plants to the load centre is called transmission. The transmission
can be classified into 2 types:
The Secondary Transmission
begins from the power station to a large
receiving station (or also known as a Sub-station) at
or near to the load centres.
Secondary => Transmission begins from receiving station to the
terminates of the various main substation
located at the strategic points inside the load centre.
The transmission voltage is to a very large extent,
determined by the economic consideration. Typical transmission voltage are 66kV,
230kV, 400kV. High voltage transmission required smaller sized conductors which
resulted in economy of copper and aluminum. But, at the same time, the cost of
insulating the lines and other expenses are increased. Hence, the economical
voltage of transmission is that for which the saving in conductor material is
not offset by the following:
Increased cost of isolating the line;
Increased size of transmission in the structures and;
Increased size of generating stations and sub-stations.
The secondary transmission voltage will be lower as the transmission distance is shorter.