How Does Earth Leakage Relay Work in Electrical Network

Figure: Earth Leakage Relay

Earth Leakage relays short ELR or also known as ground fault relays are residual current monitors in short  RCM that are used in electrical wiring to detect potentially dangerous ground fault electrical-hazard that may cause mechanical damage to cables and devices.

If fault currents become a significant value that is involved, hazardous voltages may also appear on earthed equipment, putting lives at risk.

Operational Principle of Earth Leakage Relay

An earth leakage relay checks that there is no significant leakage between the electrical supply and the earth, which means it checks the flowing current through the phase conductor and neutral conductor of the electrical circuit.

Electrical circuits and devices are in a domestic wiring, single phase, there are equal windings on a solenoid, from both phase and neutral connections.

Earth leakage relay just checks the phase and neutral current, if the two currents are equal and balanced, there is no net magnetic force generated in the solenoid. Relay no need operation.

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But, if there is a leak to earth at any point of the circuit, the currents pass through anywhere. The current in the phase and neutral will not be balanced during this situation. A net magnetic force will be generated which is used to operate the relay and trip the breaker.

The advantage of an earth leakage relay is that it does not need any external DC or AC supply to operate the relay coil. The whole system of earth leakage relay is self-contained to enable the trip.

You may find the operation principle of the earth leakage relay in the above figure where a single phage working procedure is shown. At electrical substations and other large electrical installations where a three-phase system is used, Three phase relay also works in the same principle. 

The lines would be connected via current transformers, and the tripping would be by external high-voltage circuit breakers. However, earth leakage detection relies on checking for balanced currents in the supply lines and tripping the system if the balance is disturbed by leakage to earth.

Different Between Earth leakage relay and Earth Fault Relay

Earth Leakage relay: We found from above that the earth leakage relays are used to sense the small magnitude of currents in electrical wiring systems in domestic or industrial circuits. These relays are designed in such a way that whenever they sense a preset value like 10mA and 3A,  it trips the circuit breaker and interrupts the flow of current. 

Earth leakage relays can be found in domestic distribution boards and are used to sense insulation failures and prevent electric shocks.

Earth fault relays: Earth fault relays are used in high and medium-voltage systems and transformers. The working principle is almost the same just this relay is capable of sensing greater fault currents. The contacts of the earth fault relay are connected to the trip circuit of circuit breakers at the output side of the transformer. Hence on the detection of a fault, the earth fault relay trips the circuit breaker.

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