THE INDUCED TORQUE IN AN AC MACHINE
During normal operation of ac machines (motors and generators), there are two magnetic fields: a magnetic field from the rotor and another from the stator. A torque is induced in the machine due to the interaction of the two magnetic fields.
A synchronous machine is illustrated in Fig. 5.8. A magnetic flux density BR is produced by the rotor, and a magnetic flux density BS is produced by the stator. The induced torque in a machine (motors and generators) is given by
The magnetic fields of the synchronous machine shown in Fig. 5.8, are rotating in a counterclockwise direction. What is the direction of the induced torque on the rotor of the machine?
By applying the right-hand rule to the equation of the induced torque, we see that the induced torque is clockwise. It is opposing the direction of rotation of the rotor. Therefore, this machine is working as a generator.