Electricity is transmitted by underground cables or overhead lines on poles or towers over considerable distances. The Libes, which are usually steel-cored, aluminum or hard drawn copper, are called the transmission lines. Transmission of electric power is usually at very high voltage and at low frequency in the range of 50 cycles per second (referred to as 50 Hertz or 50 Hz) in most part of the world, and up to 60 Hz in some countries. The reason for generating and transmitting at higher voltages than required in premises and appliance will be discussed later during our study of the associated components of the transmission systems.
