What is the primary function of a protective relay in a power system?
A
To interrupt the fault current
B
To detect abnormal conditions and initiate breaker operation
C
To generate electrical power
D
To regulate system frequency
Analysis & Theory
Protective relays detect faults or abnormal conditions and send a signal to the circuit breaker to isolate the fault.
Which of the following is NOT a method of classifying protective relays?
A
According to the type of input
B
According to operating time
C
According to voltage rating
D
According to construction and technology
Analysis & Theory
Relays are not classified based on voltage rating. Common classifications are based on input, timing, and technology.
Which relay operates when the current exceeds a preset value?
Analysis & Theory
Over-current relays operate when the current rises above a predefined threshold, indicating a possible fault.
Differential relays operate based on:
B
Difference in power factor
C
Difference in current entering and leaving the protected zone
D
Difference in frequency
Analysis & Theory
Differential relays compare incoming and outgoing currents; a significant difference indicates a fault within the protected equipment.
Which of the following is a **time-dependent** relay?
D
Microprocessor-based relay
Analysis & Theory
Induction-type relays operate with a time delay and are typically used in over-current protection systems.
Electromagnetic relays are classified under:
Analysis & Theory
Electromagnetic relays are conventional or electromechanical relays that use magnetic fields for operation.
Which relay is used for distance protection of transmission lines?
C
Impedance (Distance) relay
Analysis & Theory
Distance or impedance relays measure impedance between the relay location and the fault, used in transmission line protection.
Static relays differ from electromechanical relays in that they:
C
Have no moving parts and use electronic circuits
D
Cannot be used for over-current protection
Analysis & Theory
Static relays use solid-state components and do not have moving parts, offering higher reliability and faster operation.
Which of the following is a characteristic of numerical relays?
A
Work based on analog signals only
C
Are based on microprocessors and can perform multiple functions
D
Require mechanical movement to operate
Analysis & Theory
Numerical relays are programmable and perform multiple functions using digital signal processing (DSP) and microprocessors.
Relays that operate without intentional time delay are known as:
Analysis & Theory
Instantaneous relays trip the breaker immediately after detecting a fault, with no intentional time delay.