All you need to know about earth leakage relay
The presence of any faulty currents may cause wires to overheat or lead to hazardous voltages emerging on earthed equipment, causing fire or life-threatening hazards. To avoid situations like these, protective devices capable of disconnecting energy from the load, are required. One such protective device is the Earth Leakage Relay.
Earth Leakage Relay as the name suggests is an electronic device that detects earth leakages/failures. It is made of two very important transformers that help it measure the earth leakage current. These are (a) the toroidal transformer and (b) the core balance transformer. Other features like time operating characteristics with adjustable trip sensitivity and delay also come in handy. Any unidentified fault activates the trip function of the relay switching the control circuit.
How Does an Earth Leakage Relay Work?
The toroidal transformer is capable enough to detect fault currents even at extremely low levels. The high-quality magnetic core of the toroid enables it to do so. And the core balance transformer helps in directly measuring the residual current. The presence of a homopolar component is significant to an earth default. A toroidal transformer is used to measure this component by putting it around three phases + neutral, phase + neutral, or the earth connection. If there is a defect, the balance is disrupted else the vector sum of these currents remains null i.e. 0, depicting the absence of any leakage current.
The toroid’s job is to continuously detect the fault current’s value. And if any fault is detected, it passes a signal to the residual current relay which further switches its output connections to the shunt-trip to open the circuit breaker.
Why Is an Earth Leakage Relay Needed?
The compact residual current device comes with a restrictive sensitivity of only up to 1000mA whereas an earth leakage relay can detect leakage of a 400A–6300A busbar.
Current flows in large quantities from the live conductor to the earth. If accidentally it meets the ground component of any electrical circuit or device, an Earth Fault Current may occur. The earth fault relay is a device that detects earth faults and earth fault currents. Connected to the grounding wire, the Earth Leakage Relay detects any potential difference across the earth fault relay, and sends a signal to the circuit breaker, causing the circuit to trip or disconnecting the main power supply.
However, the Earth Leakage Relay has one disadvantage. Being a voltage-operated device, it can only function in case of multiple faults. Earth Leakage Relays are commonly employed where there is a possibility of a large earth fault like electrical substations and transformer systems.