A protective relay is an automatic device that detects abnormalities in an electrical circuit and closes its contacts. This action completes the circuit breaker 's trip coil circuit, causing the breaker to trip and disconnect the faulty section from the healthy circuit., lightning strikes, tree contact) and permanent faults (e. Automatic reclosing operation. The rectangular devices are test connection blocks, used for testing and isolation of instrument transformer circuits. It functions as a watchdog by constantly surveying multiple system components including voltage, current, frequency, and phase angle.