🔌 Electrical Protection Objective Questions (With Choices) 1. What is the main purpose of electrical protection systems? A. Increase voltage B. Reduce power loss C. Detect faults and isolate them D. Improve insulation ✅ Correct Answer: C 2. Which relay is used to protect equipment from overload? A. Differential Relay B. Distance Relay C. Overcurrent Relay D. Buchholz Relay ✅ Correct Answer: C 3. In a transformer, the Buchholz relay detects: A. Overvoltage B. Short circuit C. Gas accumulation due to internal fault D. Earth fault ✅ Correct Answer: C 4. Which of the following devices operates first during a fault? A. Circuit breaker B. Current transformer C. Protective relay D. Fuse ✅ Correct Answer: C 5. Which relay is used for protection against earth faults? A. Overvoltage Relay B. Differential Relay C. Earth Fault Relay D. Distance Relay ✅ Correct Answer: C 6. What is the function of a CT (Current Transformer) in a protection system? A. Reduces voltage B. Isolates circuit C. Steps down current for measurement D. Opens circuit during fault ✅ Correct Answer: C 7. Which type of relay is used for transmission line protection over long distances? A. Earth fault relay B. Distance relay C. Overload relay D. Thermal relay ✅ Correct Answer: B 8. What does an IDMT relay stand for? A. Inverse Direction Maximum Time B. Instantaneous Delay Minimum Trip C. Inverse Definite Minimum Time D. Internal Definite Magnetic Trip ✅ Correct Answer: C 9. Fuse operation is based on: A. Magnetic flux B. Thermal effect of current C. Chemical effect of current D. Electromagnetic induction ✅ Correct Answer: B 10. Which protection scheme is used in transformers to detect internal faults? A. Differential protection B. Overcurrent protection C. Earth leakage protection D. Reverse power protection ✅ Correct Answer: A 11. Relay coordination ensures: A. Fastest tripping for all faults B. Selective tripping of nearest breaker C. All breakers trip together D. Voltage control ✅ Correct Answer: B 12. The backup protection should operate when: A. Primary protection fails B. Load exceeds capacity C. Voltage drops D. Frequency drops ✅ Correct Answer: A 13. What is the operating principle of a differential relay? A. Time delay B. Phase difference C. Current difference between input and output D. Voltage comparison ✅ Correct Answer: C 14. A thermal overload relay operates based on: A. Voltage B. Temperature C. Frequency D. Current ✅ Correct Answer: B 15. Which type of protection is typically used for motors? A. Distance protection B. Reverse power protection C. Overload and phase failure protection D. Lightning arrestor ✅ Correct Answer: C 16. What is the main function of a lightning arrester? A. Overcurrent protection B. Earth fault detection C. Overvoltage diversion to ground D. Current balancing ✅ Correct Answer: C 17. A relay that operates when a set value of power is exceeded is called: A. Overcurrent relay B. Directional relay C. Overpower relay D. Overvoltage relay ✅ Correct Answer: C 18. Under-frequency protection is mainly used to protect: A. Generators B. Transformers C. Capacitors D. Circuit breakers ✅ Correct Answer: A 19. Directional relays respond to: A. Magnitude only B. Phase angle between voltage and current C. Frequency D. Temperature rise ✅ Correct Answer: B 20. Instantaneous relay operates: A. Without intentional time delay B. With minimum current C. Based on voltage variation D. With a fixed time delay ✅ Correct Answer: A