Types of Electrical Relays

Types of Electrical Relays:

In this post will see a brief understanding of various types of electrical relays.

What is relay? why is it required in the Circuit?

A relay is a device that detects the fault and initiates the operation of the circuit breaker to isolate the defective element from the rest of the system.

Classification of Relays

The electrical relays consist of one or more elements which are actuated by the electrical quantities of the circuits in which they are connected.They relays can also be classified according to their operating characteristics as detailed below:

1. Solenoid type relays

They consists of a solenoid into which moves an iron core or plunger. The operation of the relay depends on the movement of plunger.

2. Attracted armature type relays

The principle is based on the current rating of the circuit in which this type of relay is connected. As soon as the current rating of the circuit increases beyond the normal. The iron armature is attracted by the magnetic force produced by the non-desired current flowing in the relay.

3. Moving coil type relays

These relays have a coil which moves in a magnetic field provided by the permanent magnet.

4. Electrodynamic type relays

These are the relays which consists of a coil as moving component and this coil moves in an electromagnetic field.

5. Induction type

They have a metal disc or cylinder placed in an alternating magnetic field.  A rotating torque is produced in the disc by the interaction of eddy current produced in it and the alternating field.

6. Directional or reverse current type

The relay is actuated only when the direction of the current is reversed or the phase angle of the current takes up a phase displacement more than the desired value. The relay is compensated for all in voltage generally.

7. Directional or reverse power type

This type of relay is actuated when applied voltage and current attain a certain specified phase displacement. No undervoltage compensation is provided.

8. Under voltage, under current and under power relay

The relay is actuated when the rated voltage, current or power falls below the specified values.

9. Over voltage, current or over power relay

The principle of operation of this type of relay is similar to that of under voltage, under current or under power, but is actuated only when the voltage, current or power rises above a certain specified value.

10. thermal relay

The principle is similar to that of thermal ammeter or a voltmeter. The heat reduced by the current in the relay element is used to actuate it.

11. Differential relay

The operation of the relay is dependent on the difference in magnitude or phase of current or voltage.

12. Distance relay

The principle of this type of relay is dependent on voltage to current ratio or is dependent on the current carried by the relay element.

Based on the time of response:

1. Instantaneous:

In this type of relays, no time is lost between operation of the relay and tripping of the contacts.

2. Definite time lag:

In this type of relays a definite time elapses between relay operation and operation of the tripping contacts. This elapse of time is independent of the fault current to any other quantity on which the relay operation is dependent.

3. Inverse time lag:

Here the time elapsed between the relay operation and operation of the tripping contact is inversely proportional to the magnitude of the fault current or any other quantity causing relay operation.

4. Inverse definite minimum time lag:

In this case the operation of the relay is inversely proportional to the value of the current or voltage or any other quantity. The operation time of the relay tends to a definite minimum time.

Read More:
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