Application of Relays in Electrical

Relays used in the power system network are put to use in different ways depending on variables such as fault current, protection methods, and more. Over Current relays, Distance relays, Differential relays, etc. are just some of the many types of relays that can be found. Each of these relays serves a unique function and is put to a variety of other uses.

How do I determine which relay to use in my system? is a must-have for any professional in the field of electrical engineering. To determine which relay is necessary for our system, we will observe its actual deployment.

Different Types of Relay

Different types of relays can be used in the following scenarios:

1. Application of Over current relays:

Over current relays have two primary uses: protecting against ground faults and protecting against phase faults. The magnitude of a fault dictates which relays are chosen.

application of relays – relay selection method 1

Instead of using expensive distance protection, over current protection is employed in places where that would be impractical or too expensive. In situations where distance schemes are used for primary protection, over-current protection is typically employed as a secondary measure.

Learn about several Over current relay protection schemes.

Protective Measures against Earth Faults and Overcurrents

2. Application of Distance relays

When over current relaying takes too long, think about switching to a distance relay instead.

Transmission over a long distance is typical

In cases where rapid automatic reclosing isn’t required for structural integrity.
A fault delay of up to a few minutes is allowed.
Selectivity in distance relays is achieved via impedance rather than current.

Various Forms of Relay for Long Distance Use:

In the case of Ground fault relaying

Because ground resistance can fluctuate widely, fault resistance fluctuations should have little to no effect on a ground distance relay.

That’s why reactance relays are so popular for use in grounding systems.

Relaying a phase fault

For short line lengths, arc resistance has almost no effect on the Reactance relay. The arc resistance is high in comparison to the line impedance for short transmission lines.

Longer transmission lines are more prone to severe synchronizing power surges because of the increased distance that electricity must travel. Given their compactness in R-X diagrams, Mho relays are the preferred choice for these lines.
Transmission Lines of Average Length Impedance Relays are used for transmission lines of average length. Compared to reactance and mho relays, an impedance relay is less vulnerable to arcs.

3. Differential Relays Application

Differential protection is standard on large appliances like transformers, generators, and motors. Two or more identical electrical quantities (voltage, current, etc.) can trigger a differential relay’s response (I1-I2)

application of relays – relay selection method