1. The main objective of protection coordination is to:
(A) Ensure selective isolation of only the faulty section
(B) Trip the entire system during faults
(C) Increase system impedance
(D) Maintain load power factor
2. Proper coordination between protective devices ensures:
(A) Minimum disruption to the power system during faults
(B) Complete shutdown during faults
(C) Maximum fault current flow
(D) Decrease in relay sensitivity
3. Protection coordination involves setting:
(A) Relay current, time, and pickup values
(B) Generator excitation levels
(C) Transformer tap settings
(D) Power factor correction capacitors
4. Time grading in protection coordination is used to:
(A) Ensure that relays operate in a proper sequence
(B) Speed up tripping at all points
(C) Reduce voltage drops
(D) Increase current rating
5. In time-graded systems, the relay nearest to the fault:
(A) Operates first
(B) Operates last
(C) Does not operate
(D) Waits for backup relay
6. Current grading is used when:
(A) Fault current decreases with distance from the source
(B) Voltage increases along the line
(C) Load varies frequently
(D) Frequency is unstable
7. The coordination between primary and backup relays ensures:
(A) System reliability and continuity of supply
(B) Simultaneous tripping
(C) Elimination of load current
(D) Reduction in system impedance
8. The coordination time interval between primary and backup relays is typically:
(A) 0.3 to 0.5 seconds
(B) 2 to 3 seconds
(C) 5 to 10 seconds
(D) Less than 0.1 seconds
9. The term “grading margin” refers to:
(A) The time difference between operation of successive relays
(B) The current setting of a relay
(C) The voltage rating of circuit breakers
(D) The impedance of a line
10. Inverse Definite Minimum Time (IDMT) relays are used because:
(A) They provide both current and time grading
(B) They operate instantly for all faults
(C) They are independent of fault current
(D) They are cheaper than static relays
11. The total grading margin includes:
(A) Circuit breaker time, relay overshoot time, and safety margin
(B) Only relay operating time
(C) Only circuit breaker delay
(D) Power factor correction time
12. For coordination purposes, relays are arranged:
(A) From load end to source end
(B) Randomly
(C) From source to load
(D) Based on voltage level only
13. Coordination of overcurrent relays is most effective in:
(A) Radial distribution systems
(B) Ring main systems
(C) Interconnected networks
(D) Isolated systems
14. The main disadvantage of time grading is:
(A) Longer clearing time for distant faults
(B) High operating cost
(C) High relay sensitivity
(D) Unstable operation
15. Directional relays are used for coordination in:
(A) Ring main or interconnected systems
(B) Simple radial systems
(C) Isolated feeders only
(D) DC networks
16. Selectivity in protection means:
(A) Only the faulty part of the system is isolated
(B) Entire system is disconnected
(C) Relays operate without discrimination
(D) Delay in tripping of primary relays
17. Backup protection is provided to operate when:
(A) Primary protection fails
(B) There is no fault
(C) Load is disconnected
(D) System is under maintenance
18. The primary protection should operate:
(A) Faster than the backup protection
(B) Slower than backup protection
(C) Simultaneously with backup
(D) With manual control
19. In coordination of fuses and relays, fuses should:
(A) Operate first for downstream faults
(B) Operate last
(C) Not operate at all
(D) Operate for overloads only
20. Coordination between fuses and reclosers is essential to:
(A) Prevent unnecessary fuse blowing during temporary faults
(B) Increase fuse speed
(C) Eliminate circuit breakers
(D) Maintain overvoltage conditions
21. In distribution systems, coordination is most commonly performed using:
(A) Time-current characteristic curves
(B) Voltage drop curves
(C) Power factor graphs
(D) Frequency deviation curves
22. The ideal coordination of relays ensures that:
(A) Backup operates only when the primary fails
(B) Both operate together
(C) Backup always trips first
(D) System trips entirely
23. The selectivity of protection system depends on:
(A) Relay type, time setting, and coordination margin
(B) Transmission voltage
(C) Cable insulation
(D) Power factor
24. The operating time of an IDMT relay is:
(A) Inversely proportional to fault current
(B) Directly proportional to voltage
(C) Independent of fault current
(D) Constant
25. In a coordinated system, the relay near the source acts as:
(A) Backup protection
(B) Primary protection
(C) No protection
(D) Instantaneous trip device
26. Poor protection coordination may lead to:
(A) Unnecessary outages or cascading trips
(B) Improved selectivity
(C) Faster system restoration
(D) Stable voltage profile
27. Coordination of differential relays is generally:
(A) Not required because they are inherently selective
(B) Always required
(C) Achieved through time delay
(D) Done with voltage settings
28. The term “zone of protection” refers to:
(A) The section of system covered by a particular relay
(B) Total substation area
(C) Physical distance between two buses
(D) Power flow direction
29. In multi-relay coordination, overlapping zones of protection are used to:
(A) Ensure no portion of the system is left unprotected
(B) Reduce fault current
(C) Increase voltage level
(D) Avoid relay operation
30. The main goal of protection coordination is to achieve:
(A) Selectivity, sensitivity, speed, and reliability
(B) Maximum current flow
(C) Continuous overloading
(D) Power factor improvement