Relay protection consists of two parts

Relay protection consists of the primary sensing part and the secondary tripping part.

Primary Part

The primary part of relay protection includes the current or voltage transformers that sense abnormal conditions in the electrical system. These transformers detect overcurrent, overvoltage, or other fault conditions and feed the measured signals to the relay. This part is responsible for monitoring the protected zone and initiating the relay operation when a fault occurs, ensuring that the system can respond quickly to prevent damage to equipment and maintain system stability .

Secondary Part

The secondary part includes the circuit breaker (CB), the relay's operating coil, and the tripping circuit. Once the relay detects a fault, it closes its contacts, completing the trip circuit and energizing the circuit breaker coil. This action isolates the faulty section from the rest of the system, protecting equipment and maintaining operational continuity. The secondary part may operate on AC or DC power and ensures the relay's decision is executed effectively .

Summary

In essence, relay protection is divided into two parts:

1. Primary sensing part – detects abnormal electrical conditions using transformers and relays.
2. Secondary tripping part – executes the isolation of the faulted section via circuit breakers and trip circuits. This division ensures both accurate fault detection and rapid fault isolation, which are critical for the safety and reliability of power systems .