AC MACHINE FUNDAMENTALS:THE INDUCED VOLTAGE IN AC MACHINES

THE INDUCED VOLTAGE IN AC MACHINES

Just as a rotating magnetic field can be produced by three-phase set of currents in a stator, a three-phase set of voltages in the coils of a stator can be produced by a rotating magnetic field.

The Induced Voltage in a Coil on a Two-Pole Stator

Figure 5.5 illustrates a stationary coil with a rotating magnetic field moving in its center.

The induced voltage in a wire is given by

The Induced Voltage in a Three-Phase Set of Coils

Figure 5.7 illustrates three coils each of Nc turns placed around the rotor magnetic field. The voltage induced in each has the same magnitude but differs in phase by 120°. The result- ing voltages in the three phases are

Therefore, a set of three-phase currents generates a rotating uniform magnetic field within the stator of the machine, and a uniform magnetic field induces a set of three-phase volt- ages in such a stator.

The rms voltage at the terminals of the machine depends on whether the stator is Y- or �- connected. If the machine is Y-connected, the terminal voltage is 3 times EA. In �-con- nected machines, the terminal voltage is the same as EA.