Protection of AC Generators and Motors Interview Questions:

Following are the below Protection of AC Generators and Motors Interview Questions and Important Questions which is very useful for interviews and exams

1. What are the abnormal conditions in a large alternator against which protection is necessary ? Discuss them briefly.

2. Explain the protection of a three-phase star-connected generator by means of a percentage differential relay.

3. Describe the general principle of operation of generator differential protection scheme. Give the 3-phase connection of the biased scheme.

4. Give a complete protection scheme for alternator.

5. Restricted earth-fault protection is provided to alternators though it does not protect complete wiring against earth fault. Justify this type of protection.

6. What are the abnormal conditions in a large alternator against which protection is necessary ? Discuss a protection scheme for an alternator against inter-turn faults.

7. Describe various protection schemes of an alternator for different faults and abnormal running conditions.

8. Describe with suitable diagrams how the stator windings of a 3-phase alternators are protected from

• Earth faults on the stator winding.
• Unbalanced current in the stator winding.
• Earth fault on the rotor winding.
• Overloading of alternator.

9. What types of protective device are used for the protection of an alternator against overheating of its (i) stator and (ii) rotor ? Discuss them in brief.

10. Discuss suitable protection schemes which are used for (i) rotor earth fault (ii) rotor open circuit of a synchronous generator.

11. Explain : A loss of excitation relay used for alternator protection.

12. What are the types of faults that are likely to occur in a 3-phase induction motor ? If the motor is not fully loaded, is it necessary to provide protection against single phasing ? Explain why ?

13. What are the types of faults that are likely to occur in a three-phase induction motor ? Distinguish between short-circuit protection, overload protection and earth-fault protection of motor.

14. Explain the term “single phasing”. In what form such protection is provided in case of a large 3-phase induction motor ? If the motor is not fully loaded, is it necessary to provide protection against single phasing ? Explain why.

15. Write short notes on the following :

• Generator faults.
• Protection of alternator.
• Overload protection of alternator.
• Self balance protection system.
• Inter-turn fault protection of alternators.
• Overspeed protection of alternators.
• Loss of excitation protection of alternators.
• Protection of small motors.