Protection coordination and relay settings – MCQs – EE

1. The main purpose of protective relays is to:
(A) Monitor voltage only
(B) Automatically isolate faulty parts of the system
(C) Plot voltage waveforms
(D) Calculate RMS currents

2. Overcurrent relays operate based on:
(A) Frequency deviations
(B) Current exceeding a preset value
(C) Voltage dips
(D) Transformer tap position

3. Time-current characteristics (TCC) are used to:
(A) Determine relay operating time for a given current
(B) Measure system voltage only
(C) Plot reactive power
(D) Solve load flow

4. Inverse-time relays operate:
(A) Faster for smaller currents
(B) Slower for larger currents
(C) Slower for smaller currents and faster for larger currents
(D) Constant irrespective of current

5. Coordination of relays ensures:
(A) All relays operate at the same time
(B) Only primary relay operates for a fault, backup acts if needed
(C) Plotting of RMS currents
(D) Only voltage monitoring

6. Distance relays measure:
(A) Impedance of the protected line
(B) Frequency deviation
(C) Current only
(D) Power factor

7. A backup relay is intended to:
(A) Operate when primary relay fails
(B) Monitor voltage continuously
(C) Only measure transformer taps
(D) Plot load flow

8. Overvoltage relays are used to:
(A) Trip for voltage exceeding a preset value
(B) Detect overcurrent
(C) Solve short-circuit currents
(D) Step response only

9. Instantaneous relays operate:
(A) Without intentional time delay
(B) With inverse time delay
(C) Only during startup
(D) Only for voltage dips

10. Coordination study involves:
(A) Analyzing relay TCC curves
(B) Calculating FFT
(C) Step response analysis
(D) Load flow only

11. Zone-1 distance protection typically covers:
(A) 80–90% of the line
(B) Entire network
(C) Only transformer
(D) Substation bus

12. Zone-2 distance protection operates with:
(A) Short intentional time delay
(B) Immediate tripping
(C) Only voltage measurement
(D) Step response

13. Relay pick-up current is:
(A) Minimum current to cause relay operation
(B) Maximum rated current
(C) Load current only
(D) Voltage magnitude

14. Differential relays operate based on:
(A) Difference of currents at two ends of equipment
(B) Absolute voltage
(C) Frequency deviation
(D) Step response only

15. Directional relays detect:
(A) Fault current direction
(B) Voltage only
(C) Step response
(D) Load flow

16. Overcurrent relay settings include:
(A) Time dial and pick-up current
(B) Voltage magnitude
(C) Transformer tap
(D) Load power factor

17. Relay grading ensures:
(A) Proper coordination between primary and backup relays
(B) Equal current through all relays
(C) Constant system voltage
(D) Step response only

18. Maximum fault current is used to:
(A) Determine relay settings and breaker ratings
(B) Plot voltage curves
(C) Measure frequency only
(D) Step response

19. Instantaneous overcurrent relays are:
(A) Time-delayed
(B) Operate immediately when current exceeds pick-up
(C) Only for voltage dips
(D) Load flow dependent

20. Coordination margin is:
(A) Time interval between primary and backup relay operation
(B) Voltage difference across line
(C) Load current difference
(D) Step response

21. In solidly grounded systems, ground fault protection uses:
(A) Zero-sequence current relays
(B) Distance relays
(C) Differential relays
(D) Step response only

22. Transformer protection may include:
(A) Differential, overcurrent, and Buchholz relays
(B) Step response only
(C) Load flow only
(D) RMS voltage measurement

23. Overload protection of motors is usually provided by:
(A) Thermal relays
(B) Differential relays
(C) Distance relays
(D) Step response only

24. Relay time setting should account for:
(A) Coordination with downstream relays
(B) Transformer rating only
(C) Line impedance only
(D) Voltage sag

25. Modern digital relays can provide:
(A) Communication, event recording, and self-testing
(B) Only mechanical operation
(C) Step response only
(D) Load flow analysis

26. Protective relays can be:
(A) Electromechanical, static, or digital
(B) Only solid-state
(C) Only step response blocks
(D) Load flow dependent

27. Relay CT saturation affects:
(A) Accurate fault current measurement
(B) Step response
(C) Voltage only
(D) Load flow

28. Coordination studies are typically performed using:
(A) Relay TCC curves and software tools
(B) FFT analysis only
(C) Step response only
(D) Voltage sag plots

29. Directional overcurrent relays are used in:
(A) Ring or meshed networks
(B) Radial networks only
(C) Step response only
(D) Load flow analysis

30. Proper relay setting ensures:
(A) Selective isolation of faulted sections
(B) Step response only
(C) Constant voltage across network
(D) Plotting of RMS values