1. The primary function of a protective relay is to:
(A) Detect abnormal conditions and initiate circuit breaker operation
(B) Measure system voltage
(C) Regulate power factor
(D) Control load flow
2. Protective relays are part of the:
(A) Protection system of electrical power networks
(B) Transmission system
(C) Power generation system only
(D) Load management system
3. The main requirement of a good protective relay is:
(A) Reliability and selectivity
(B) High cost
(C) Delay in operation
(D) Manual reset
4. The operating time of a relay is the time between:
(A) Fault occurrence and relay contact operation
(B) Fault occurrence and circuit breaker closing
(C) Circuit breaker tripping and reclosing
(D) Relay reset and breaker operation
5. A protective relay must be:
(A) Fast, selective, and reliable
(B) Slow and economical
(C) Inverse in timing only
(D) Voltage-dependent only
6. The selectivity of a relay means:
(A) Ability to discriminate between faulty and healthy sections
(B) Ability to operate for all faults
(C) Ability to sense voltage only
(D) Time delay in operation
7. The reliability of a relay means:
(A) It operates only when required
(B) It always operates
(C) It never operates
(D) It requires manual reset
8. Sensitivity of a relay refers to:
(A) Its ability to respond to the smallest fault current
(B) Its speed of operation
(C) Its insulation strength
(D) Its cost
9. The speed of operation of a relay depends mainly on:
(A) Type of relay and fault severity
(B) Voltage rating of the system
(C) Load connected
(D) Transformer capacity
10. An instantaneous relay operates:
(A) Without any intentional time delay
(B) After a preset delay
(C) Only at high voltage
(D) After 1–2 seconds
11. Time delay relays are used to:
(A) Achieve coordination between successive protective devices
(B) Reduce circuit breaker rating
(C) Increase voltage
(D) Eliminate harmonics
12. An inverse time relay operates:
(A) Faster for higher fault currents
(B) Slower for higher fault currents
(C) Independently of current magnitude
(D) Only for voltage faults
13. Inverse-time overcurrent relays are generally used for:
(A) Feeder protection
(B) Generator protection
(C) Transformer differential protection
(D) Busbar protection
14. The most commonly used relay for transmission line protection is:
(A) Distance relay
(B) Overvoltage relay
(C) Thermal relay
(D) Frequency relay
15. Differential relays operate when:
(A) The difference between incoming and outgoing currents exceeds a set value
(B) System voltage drops
(C) Load current increases
(D) Frequency changes
16. Directional relays are used to:
(A) Detect the direction of fault current flow
(B) Measure active power
(C) Control frequency
(D) Maintain voltage regulation
17. Overcurrent relays respond to:
(A) Magnitude of current
(B) Magnitude of voltage
(C) Power factor
(D) Frequency
18. Overvoltage relays operate when:
(A) Voltage exceeds a predetermined value
(B) Current decreases
(C) Frequency changes
(D) Power factor lags
19. The earth fault relay operates when:
(A) Current flows from line to ground
(B) Load increases
(C) Power factor improves
(D) Phase current balances
20. Thermal relays protect equipment from:
(A) Overload conditions due to excessive heating
(B) Short circuit faults
(C) Overvoltage
(D) Under-frequency
21. Distance relays operate based on:
(A) The impedance between the relay and fault point
(B) The frequency of the system
(C) The phase angle between voltage and current
(D) The power flow
22. Differential protection is not suitable for:
(A) Long transmission lines
(B) Transformers
(C) Generators
(D) Busbars
23. Negative sequence relays are used for:
(A) Detecting unbalanced loads in generators
(B) Detecting overvoltage
(C) Detecting undercurrent
(D) Detecting power factor
24. Frequency relays are mainly used in:
(A) Generator protection schemes
(B) Transformer circuits
(C) DC systems
(D) Distribution feeders
25. A Buchholz relay is a type of:
(A) Gas-actuated relay used in oil-filled transformers
(B) Overcurrent relay
(C) Distance relay
(D) Frequency relay
26. Static relays differ from electromagnetic relays in that they:
(A) Use solid-state components instead of moving parts
(B) Are slower in operation
(C) Require mechanical motion
(D) Operate on magnetic flux
27. Numerical relays use:
(A) Microprocessors and digital algorithms for protection
(B) Electromagnets only
(C) Oil damping
(D) Rotating coils
28. The main advantage of numerical relays over traditional ones is:
(A) Multi-function capability and self-diagnosis
(B) Higher weight
(C) Manual calibration
(D) Slower operation
29. The operating coil of a relay is energized by:
(A) CT or PT secondary current or voltage
(B) Direct supply voltage
(C) Load current directly
(D) Generator excitation current
30. The ultimate goal of protective relaying is to:
(A) Ensure safety, reliability, and continuity of the power system
(B) Increase voltage regulation
(C) Control system frequency
(D) Improve power factor