Protective Relay Question & Answers May 4, 2023 By Wat Electrical This article lists 50 Protective Relay MCQs for engineering students. All the Protective Relay Questions & Answers below include a hint and a link to the relevant topic wherever possible. This is helpful for users who are preparing for their exams, interviews, or professionals who would like to brush up on the fundamentals of the Protective Relay. A protective relay is an electrical device used to detect and isolate faults in a power system. It is a critical component of a power system protection scheme, and its main function is to trip or open the circuit breaker to isolate the faulty section of the power system when a fault occurs. The protective relay operates based on the principles of electromagnetic induction and uses current and voltage measurements to determine the condition of the power system. It is designed to sense abnormal conditions, such as overcurrent, under voltage, overvoltage, or a combination of these, and trip the associated circuit breaker to prevent damage to the equipment and to protect the power system from further damage. The protective relay is typically connected to the power system through current transformers and voltage transformers, which step down the high voltage and current levels in the power system to levels that can be measured by the protective relay. There are various types of protective relays, such as overcurrent relays, differential relays, distance relays, and others, each designed to provide specific protection functions for the power system. Modern protective relays are often digital and offer advanced features such as communication capabilities, fault recording, and advanced protection algorithms. 1). What is the main function of a protective relay? To trip the circuit breaker To monitor the power system To regulate the voltage To generate power None Hint 2). The detect internal faults in equipment and trips the breaker is a function of _____________ relay? Protective Overcurrent Differential Distance None Hint 3). The feeder protection is an example of ______________ type? Overcurrent Differential Distance Directional None Hint 4). Which one of the following can be adjusted for different levels of fault current and trip times? Differential Distance Directional Overcurrent None Hint 5). Which of the following is a limitation of ground fault relays? They are not effective for high-impedance ground faults They are more expensive than other types of relays They are more complex to set up and program They are less reliable than other types of relays None Hint 6). What is the purpose of the time delay in a ground fault relay? To allow for coordination with other protective devices To increase the sensitivity of the relay To reduce false trips caused by transients or other temporary conditions To increase the speed of the relay's operation None Hint 7). How does a ground fault relay detect a ground fault? By measuring the zero-sequence current in the power system By measuring the phase-sequence current in the power system By measuring the voltage between phases in the power system By measuring the voltage between phases and ground in the power system None Hint 8). Which of the following is a common type of ground fault relay? Zero-sequence relay Overcurrent relay Differential relay Distance relay None Hint 9). What is the most common application of a zero-sequence relay? Overcurrent protection Distance protection Differential protection Ground fault protection None Hint 10). What is the most common type of protective relay used in power systems? Overcurrent relay Differential relay Distance relay Directional relay None Hint 11). The detect faults based on the impedance or distance of the fault from the relay location is a function of _____________ relay? Protective Overcurrent Differential Distance None Hint 12). The transformer protection is an example of ______________ type? Overcurrent Differential Distance Directional None Hint 13). Which of the following is an advantage of using numerical relays for protection? They are less expensive than electromechanical relays They have a faster operating time than electromechanical relays They require less maintenance than electromechanical relays They are more accurate than electromechanical relays None Hint 14). Which of the following is not a type of numerical relay? Overcurrent relay Distance relay Differential relay Electromechanical relay None Hint 15). What is the main advantage of using a numerical relay over an electromechanical relay? Faster operation time Lower cost More reliable Easier to install None Hint 16). Which of the following is a disadvantage of using a numerical relay? More complex to program and set up Higher cost Less accurate measurement of power system parameters Limited functionality None Hint 17). Which type of numerical relay is used to protect transmission lines? Overcurrent relay Distance relay Differential relay Ground fault relay None Hint 18). Which one of the following requires good CT saturation and polarity characteristics? Differential Distance Directional Overcurrent None Hint 19). The transmission line protection is an example of ______________ type? Overcurrent Differential Distance Directional None Hint 20). Which of the following types of protective relays is used to protect transformers? Overcurrent relay Differential relay Distance relay Directional relay None Hint Protective Relay MCQ for Exams 21). The detect faults based on the direction of current flow is a function of _____________ relay? Protective Overcurrent Differential Directional None Hint 22). What is the basic principle of operation of an overcurrent relay? It measures the voltage across a circuit breaker It measures the current flowing through a circuit breaker It measures the power consumed by a circuit breaker It measures the frequency of the AC voltage None Hint 23). What is the pickup value of an overcurrent relay? The minimum current required to operate the relay The maximum current that the relay can handle without damage The ratio of the secondary to the primary current of the transformer The impedance of the relay None Hint 24). What is the purpose of time grading in overcurrent protection? To ensure that the correct relay operates during a fault To ensure that the correct circuit breaker is tripped during a fault To ensure that the relay operates within a specified time limit To ensure that the relay operates before any backup protection devices None Hint 25). What is the purpose of a directional overcurrent relay? To protect against overcurrent in any direction To protect against overcurrent flowing in a specific direction To protect against overvoltage conditions To protect against undervoltage conditions None Hint 26). The generator protection is an example of ______________ type? Overcurrent Differential Distance Directional None Hint 27). Which one of the following requires accurate line parameters, can be affected by faults outside the protected zone? Differential Distance Directional Overcurrent None Hint 28). Which of the following is a disadvantage of using digital relays for protection? They are expensive They require a lot of maintenance They are not accurate They are vulnerable to cyber attacks None Hint 29). Which type of relay is used for protection against generator faults? Differential relay Distance relay Overcurrent relay Earth fault relay None Hint 30). What is the purpose of a backup relay? To provide a redundant layer of protection in case the primary relay fails To operate before the primary relay to trip the circuit breaker faster To provide a delay before the primary relay operates To provide protection against both overvoltage and undervoltage conditions None Hint 31). The motor protection is an example of ______________ type? Overcurrent Differential Distance IDMT None Hint 32). Which one of the following can be affected by changes in system configuration or fault location? Differential Distance Directional Overcurrent None Hint 33). What is a protection relay? A device that protects electrical systems from damage A device that measures the amount of current in a system A device that regulates the voltage in a system A device that stores energy in a system None Hint 34). Which type of relay is used for protection against overcurrent? Distance relay Differential relay Overcurrent relay Underfrequency relay None Hint 35). Which type of relay is used for protection against earth faults? Distance relay Differential relay Overcurrent relay Earth fault relay None Hint 36). Which of the following is the main function of a protection relay? To disconnect the power supply To regulate the voltage To detect a fault and initiate a trip signal To increase the frequency of the system None Hint 37). Which type of relay is used for protection against transformer faults? Differential relay Distance relay Overcurrent relay Earth fault relay None Hint 38). Which of the following is a disadvantage of using electromechanical relays for protection? They are expensive They are difficult to maintain They have a slow operating time They are not accurate None Hint 39). Which type of relay is used for protection against motor faults? Differential relay Distance relay Overcurrent relay Earth fault relay None Hint 40). The detect and isolate faults in a power system is a function of _____________ relay? Protective Overcurrent Differential Distance None Hint Protective Relay MCQ for Quiz 41). What does IDMT stand for in relation to protective relays? Instantaneous Differential Multiple Time Inverse Definite Minimum Time Induction Differential Motor Timing Insulation Detection and Monitoring Technology None Hint 42). What is the basic operating principle of an IDMT relay? It detects the direction of current flow It detects the impedance or distance of the fault It operates on a fixed time delay It operates on an inverse time characteristic with current magnitude None Hint 43). What is the advantage of using an IDMT relay over a fixed time delay relay? It provides more accurate and selective protection It is less expensive to install and maintain It can operate on both overcurrent and undercurrent faults It can detect faults at a greater distance from the relay location None Hint 44). What is the typical characteristic curve of an IDMT relay? A straight line A curved line with a slope of 1 A curved line with a slope greater than 1 A curved line with a slope less than 1 None Hint 45). What is the basic principle of operation of a differential relay? It detects the impedance or distance of the fault It compares the current flowing into a system with the current flowing out of the system It detects the direction of current flow It operates on a fixed time delay None Hint 46). What is the purpose of a restraint current in a differential relay? To limit the magnitude of the differential current To increase the sensitivity of the differential relay To improve the selectivity of the differential relay To reduce the operating time of the differential relay None Hint 47). Restraint current is used to limit the magnitude of the differential current and prevent the relay from tripping on external faults (I1 - I2)/I2 x 100% (I2 - I1)/I1 x 100% (I1 - I2)/(I1 + I2) x 100% (I2 - I1)/(I1 + I2) x 100% None Hint 48). What is harmonic restraint in a differential relay? A technique used to reduce the effects of harmonics on the differential relay A technique used to improve the selectivity of the differential relay A technique used to reduce the operating time of the differential relay A technique used to increase the sensitivity of the differential relay None Hint 49). What is the application of a circulating current differential relay? Protecting transmission lines Protecting transformers and generators Protecting motors Protecting busbars None Hint 50). The detect excessive current flow in a circuit and trips the breaker is a function of _____________ relay? Protective Overcurrent Differential Distance None Hint Read more about Transformer Time's up
