CHAPTER 5 - Three-Phase System

Abstract

This chapter describes the three-phase system. The practical three-phase alternating current (AC) generator generates a supply by the relative motion between an approximately sinusoidally distributed magnetic field and the conductors that will carry the AC load currents. The conductors always move relatively at right angles to this magnetic field. A number of advantages may be obtained by interconnecting the three windings. There are two common methods of doing this. One is called the star connection, and the other is called the delta or mesh connection. No current will flow in the three-phase AC generator winding unless a load is connected to the machine. Any three corresponding ends of the windings, that is, the three starts or the three finishes, are joined together; this junction is called the star point. If a conductor is connected to the star point, it is called the neutral conductor. In the delta or mesh connection, the start of one winding is connected to the finish of another winding, and this is repeated until a closed circuit is obtained. This connection is permitted because the phasor sum of the three-phase voltages acting around the circuit is zero.