ABSTRACT
A multiphase alternating current (ac) source produces a rotating magnetic ›eld inside ac motors, which causes the shaft of the motor to spin. Before we explain how an ac machine rotates, we need to understand the concept of rotating magnetic ›elds. Consider the conceptual diagram of the stator of a three-phase machine shown in Figure 12.1. The ›gure shows three windings mounted symmetrically inside a hollow metal tube called stator, which are shifted by 120° from each other. Each winding goes along the length of the stator on one side and then returns from the other side. If we apply a three-phase balanced voltage across the terminals of the windings, the currents of the windings create balanced three-phase magnetic ›elds inside the tube as shown in Figure 12.2.
