ABSTRACT
The purpose of the electric transmission system is the interconnection of the electric energy producing
power plants or generating stations with the loads. A three-phase AC system is used for most transmis-
sion lines. The operating frequency is 60 Hz in the U.S. and 50 Hz in Europe, Australia, and part of Asia.
The three-phase system has three phase conductors. The system voltage is defined as the rms voltage
between the conductors, also called line-to-line voltage. The voltage between the phase conductor and
ground, called line-to-ground voltage, is equal to the line-to-line voltage divided by the square root of
three. Figure 8.1 shows a typical system.
