Which type of protection relay responds to faults to either the left or right of its location?

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

Answer: (B)

A directional relay is designed to respond to faults in a specific direction, typically indicating whether power is flowing towards or away from the relay's location. This allows it to differentiate between fault conditions that occur in different sections of a network, enabling the relay to determine the direction of a fault accurately.

This capability is particularly important in radial and looped systems where faults may happen on either side of the relay. By knowing the fault's direction, the relay can make more effective decisions about breaking circuits and isolating faults to maintain system reliability and prevent damage.

In contrast, other types of relays function differently. For example, an overcurrent relay responds to excessive current without directional specifics, a distance relay is used for protecting long transmission lines and measures impedance to determine faults but doesn’t inherently focus on directionality, and a differential relay compares currents entering and leaving a section of the system to identify faults but does not determine the fault's direction relative to its position. This distinction highlights why the directional relay is suited for detecting faults to the left or right of its location.