SOLUTION

• In the case of an induction motor, the field winding is permanently short-circuited by end rings.
• In a Synchronous motor, the rotor winding is supplied with DC excitation. Now, if we eliminate the DC excitation, there are two ends of the wire available.
• Let short-circuit the two ends of the wire (or connect the two ends of variable resistors).
• Now the rotor winding of the synchronous motor is analogous to that of an induction motor.
• Therefore if we short-circuit the field winding of a synchronous motor then it will behave as an induction motor.