What type of protection relay is used to compare currents and protect the zones of an electrical system?

What type of protection relay is used to compare currents and protect the zones of an electrical system?

• A. Directional relay
• B. Overcurrent relay
• C. Differential relay
• D. Impedance relay

Answer: (C)

The differential relay is a protective device that operates by comparing the currents entering and leaving a certain section of an electrical system, such as a transformer or generator. Its primary function is to detect any differences between these currents, which can indicate faults such as short circuits or equipment failures within the protected zone. In a normal operating condition, the currents should be equal; however, if there is a fault, they will not match, and the differential relay will detect this imbalance, leading to the activation of protective measures, such as tripping a circuit breaker. This characteristic makes the differential relay highly effective for zone protection, as it ensures that only the faulty section of the system is isolated, thereby maintaining the integrity of the other areas. In contrast, other types of relays serve different purposes. For instance, the directional relay focuses on the direction of fault currents rather than comparing them, while the overcurrent relay reacts to excessive current levels without providing detailed zone discrimination. Impedance relays measure the impedance of the circuit but do not specifically compare currents at different points. Each of these relays plays a crucial role in protection schemes, but the differential relay is uniquely suited for the task of comparing currents to safeguard specific zones within the electrical system.

The differential relay is a protective device that operates by comparing the currents entering and leaving a certain section of an electrical system, such as a transformer or generator. Its primary function is to detect any differences between these currents, which can indicate faults such as short circuits or equipment failures within the protected zone.

In a normal operating condition, the currents should be equal; however, if there is a fault, they will not match, and the differential relay will detect this imbalance, leading to the activation of protective measures, such as tripping a circuit breaker. This characteristic makes the differential relay highly effective for zone protection, as it ensures that only the faulty section of the system is isolated, thereby maintaining the integrity of the other areas.

In contrast, other types of relays serve different purposes. For instance, the directional relay focuses on the direction of fault currents rather than comparing them, while the overcurrent relay reacts to excessive current levels without providing detailed zone discrimination. Impedance relays measure the impedance of the circuit but do not specifically compare currents at different points. Each of these relays plays a crucial role in protection schemes, but the differential relay is uniquely suited for the task of comparing currents to safeguard specific zones within the electrical system.