Protection relays are crucial components in electrical systems that monitor parameters such as current, voltage, frequency, and power factor. They protect against short circuits, ground faults, overvoltages, and undervoltage. They detect faults and abnormal conditions, isolate faulty system sections, and prevent further damage and downtime. In modern systems, protection relays are integrated with communication and automation technologies, enhancing reliability, fault detection accuracy, and remote monitoring and control. Electrical Engineering Online shares the top 10+ Objective MCQ Questions on Protection Relays with brief explanatory answers in this post.
What is the primary function of a protection relay in an electrical system
What is the primary function of a protection relay in an electrical system
- To control the voltage
- To regulate the frequency
- To protect equipment and circuits from faults
- To generate electricity
Correct Answer: 3. To protect equipment and circuits from faults
Explanation: The primary purpose of a protection relay is to detect and respond to electrical faults, ensuring the safety and reliability of equipment and circuits.
The distance relay is used mainly to protect against
The distance relay is primarily used to protect against
- Overvoltage
- Overcurrent
- Short circuit
- Ground fault
Correct Answer: 3. Short circuit
Explanation: Distance relays are designed to protect against short circuits, which occur when there is a direct connection between the phase conductors or between a phase conductor and the ground.
An overcurrent relay protects against
An overcurrent relay protects against
- Excessive voltage
- Excessive current
- Ground faults
- Harmonics
Correct Answer: 2. Excessive current
Explanation: Overcurrent relays protect against excessive current flowing through a circuit, which can damage equipment and cause other electrical faults.
The main advantage of a differential relay is
The main advantage of a differential relay is
- High-speed operation
- High sensitivity
- Wide operating range
- Easy installation
Correct Answer: 2. High sensitivity
Explanation: Differential relays are highly sensitive and can detect slight differences in current between two or more connected circuits, making them effective in protecting transformers, motors, and generators.
The type of relay that is widely used for motor protection
The type of relay that is widely used for motor protection
- Differential relay
- Overvoltage relay
- Overcurrent relay
- Under frequency relay
Correct Answer: 3. Overcurrent relay
Explanation: Overcurrent relays are commonly used to protect motors from excessive current, which can lead to motor overheating and damage.
The ground fault relay protects against
The ground fault relay protects against
- Overvoltage
- Overcurrent
- Short circuit
- Ground faults
Correct Answer: 4. Ground faults
Explanation: Ground fault relays are designed to detect and protect against faults that occur when a live conductor comes into contact with the ground, reducing the risk of electric shock and damage to equipment.
The type of electrical relay that serves as backup protection in case of primary relay failure is termed as
The type of electrical relay that serves as backup protection in case of primary relay failure is termed as
- Differential relay
- Auxiliary relay
- Backup relay
- Overvoltage relay
Correct Answer: 3. Backup relay
Explanation: Backup relays are designed to provide an additional layer of protection in case the primary relay fails to operate correctly.
Which type of relay is used to detect and protect against reverse power flow in generators
Which type of relay is used to detect and protect against reverse power flow in generators
- Directional relay
- Differential relay
- Overcurrent relay
- Under frequency relay
Correct Answer: 1. Directional relay
Explanation: Directional relays are used to detect the direction of power flow and protect against reverse power flow, which can damage generators.
What is the purpose of a frequency relay
What is the purpose of a frequency relay
- To regulate the voltage
- To protect against short circuits
- To control the frequency of power system
- To protect against frequency deviations
Correct Answer: 4. To protect against frequency deviations
Explanation: Frequency relays detect and protect against significant variations in the system frequency, which can indicate abnormal operating conditions or faults.
The Buchholz relay is commonly used for the protection of
The Buchholz relay is widely used for the protection of
- Transformers
- Generators
- Busbars
- Power distribution lines
Correct answer: 1. Transformer
Which type of relay is commonly used for generator protection
Which type of relay is commonly used for generator protection
- Directional relay
- Differential relay
- Overcurrent relay
- Under frequency relay
Correct Answer: 2. Differential relay
Explanation: Differential relays are commonly used for generator protection, as they can detect and respond to internal faults within the generator.
Which type of relay is used to protect transmission lines from faults
Which type of relay is used to protect transmission lines from faults
- Directional relay
- Differential relay
- Distance relay
- Overcurrent relay
Correct Answer: 3. Distance relay
Explanation: Distance relays are commonly used to protect transmission lines by measuring the impedance or distance to the fault and tripping the circuit breaker if the fault is within the predetermined range.
What is the purpose of a motor protection relay
What is the purpose of a motor protection relay
- To control the motor speed
- To protect against voltage surges
- To protect against overcurrent and overheating of the motor
- To monitor motor efficiency
Correct Answer: 3. To protect against overcurrent and overheating of the motor
Explanation: Motor protection relays are specifically designed to monitor the current flowing through the motor and protect against overcurrent conditions that could lead to motor overheating and damage.
Which type of relay is commonly used for transformer protection
Which type of relay is widely used for transformer protection
- Directional relay
- Differential relay
- Overcurrent relay
- Under frequency relay
Correct Answer: 2. Differential relay
Explanation: Differential relays are commonly used for transformer protection to detect and respond to internal faults within the transformer.