A relay is a device that detects and informs the circuit breaker about faults. This triggers circuit interruption to protect devices and other power systems. A relay can be categorised into three parts - primary winding, secondary winding and tripping circuit. The primary winding often consists of the main conductor itself. The primary winding of the Current Transformer(CT) is connected in series with circuit to be protected. The second circuit is the secondary winding of the CT, which is connected to the relay operating coil. The third circuit is the tripping circuit which consists of a source of supply, a trip coil of circuit breaker and relay stationary contacts. Under normal conditions, the voltage of the secondary winding of CT and the current flowing in the relay coil are low enough to keep relay contacts undisturbed. However, in the event of a fault, voltage across the secondary winding and the relay contacts change the status, and the circuit breaker is operated.

Fault-handling strategies for relays
Preventive maintenance is of utmost importance in relays. A combination of mechanical inspection and electrical tests, followed by required adjustments help in the early detection of faults.

Motwane offers a range of test equipment that cover the range of monitoring needs of relays. Take a look below.

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