An alternator is hooked up to a DC motor With the motor runn

An alternator is hooked up to a DC motor. With the motor running the torque is decreased to the point of the power from the alternator to the DC motor changes polarity to negative. Why would the system continue to rotate at the same speed? What are the differences between a three-phase alternator and a three phase synchronous motor?

Solution

Differences

An alternator is a synchronous generator which gives AC electrical power as output where as synchronous motor gives mechanical output.The armature reaction and excitation level (over,normal and under) cases of alternator are exactly opposite that of synchronous motor.For example Alternator will be overexcited for lagging power factor where as synchronous motor will be under excited for lagging PF.

Thank you.