What is a Protection Relay and what does it Use for

Even the most efficient electrical system is prone to faults caused by short circuits or other similar issues. A relay protection control device is a relay that eliminates these faults by tripping a circuit breaker as and when it detects a fault in the system. In doing so, the relay helps isolate the faulty component, making it easier to repair the component before it hampers the entire electrical system.

Working Principle of Protective Relays

Protective relays installed in electrical systems come with switchgear, which finds out faults in the system. Once the fault is detected, the relays trip a circuit breaker, which isolates the defective element. This is done while ensuring the rest of the electrical system continues to function without any issues.

Protective relays work by measuring one or a set of variables in an electrical configuration. These variables may include voltage, current, phase, frequency, impedance, etc, which usually come with preset values. A sensor in the relay detects any change in the values of these variables. If it does, it will send a signal indicating the type of fault, along with its location to the relay, which would then trip the circuit breaker to isolate/disconnect the faulty element from the main system.

The more recent protection relays come equipped with several sensors to measure more than a few variables, thus reducing fault times considerably and ensuring the system continues to work without any hindrance.

Different Types of Protective Relays

Some of the more common types of relay protection control devices include:

Directional Relays

These relays get activated when current flows in the opposite direction, measuring a difference between actuating and reference currents. It is commonly used with other relays for detecting faults in the system.

Overcurrent Relays

These relays get activated via the current. A predetermined pick-up value is set and the relay uses it as a threshold value to measure the current passing through the system. If the quantity of current flowing in the system exceeds the pick-up value, the relay triggers the circuit breaker to isolate the faulty element. The most common types of overcurrent relays include instantaneous relays and time relays, with some systems using a combination of both types for more operating efficiency.

Differential Relays

These relays measure the magnitude of the current that enters the circuit and compares it with the magnitude of the current that leaves it. If the difference between these two values exceeds a pickup value, the relay trips the circuit breaker.

Pilot Relays

These relays are used to monitor faults existing inside a protected line. The pilot relay works as the system’s communication channel, relaying information about the line to and from terminals located on both ends of the protected line. If the relay picks up any fault within the line, it will trigger the circuit breaker. However, it will be blocked or not function if the fault lies outside the protected line.

Uses of Protection Relays

A relay protection control device finds its use in any electrical system that needs to function with minimal faulty time and without any hindrances. As such, the majority of protection relays find their use in electrical lines, grids, power stations, etc, and any other place that relies on the continuous supply of power for functioning.