Overcurrent Relay types

In this article we will learn about overcurrent relay types. We will also know that what is working of overcurrent relay and overcurrent relay type. Here we now discus about the overcurrent relay types and working.

Overcurrent Relay types and working

Relay is sensing equipment which senses abnormal voltage and current conditions in power system and sends signals to circuit breaker to remove faulty part from rest of power system.
overcurrent relay types, types of overcurrent relay, working of over current relay
First line of defense is provided by the primary relaying equipment and second line of defense is provided by the backup relaying equipment. Backup protection operates when primary protection has failed.

Overcurrent Relay types  

overcurrent relay types, types of overcurrent relay, working of over current relay


The operating time of all over current relays tends to become asymptotic to a definite minimum value with increase in the value of current. This is inherent in electromagnetic relays due to saturation of the magnetic circuit. These are following types of over current relay.
Instantaneous Over current Relay
In this relay, time of operation of relay does not depend on the value of actuating quantity once it is more than pick up value. This is property of electromagnetic attraction types of relay. Time of operation usually .1s. It is one of the overcurrent relay types.
overcurrent relay types, types of overcurrent relay, working of over current relay

Inverse Time current Relay

In this relay, there is an inverse relationship between actuating quantity and time of operation of the relay. All electromagnetic induction types of relay are inverse time current relays to some or large extent. It depends on how core iron gets saturated. If it saturates early, it becomes definite time current relay. It is main overcurrent relay types.

Inverse Definite Minimum time current Relay

In this relay time of operation of the relay is inversely proportional to current near pick up value and for values little after that. If current increases more, then that time of operation becomes constant.

Very inverse Relay

In this type of relay, core does not saturate early, and then inverse relationship can be introduced air gap in core. So, time current characteristics are inverse for larger values of current and then become definite time curve.

Extremely Inverse Relay

In this relay, saturation occurs at much later stage and current time curve is inverse for larger value of current curve.

Differential Relay

The principle of operation depends on a simple circulating current principle, where the difference of the currents of the two CT s flow through the relay under normal conditions or even under faults outside the protected section.

Protective Relay

Protective Relay and systems detect abnormal condition like fault in electrical circuit and operate automatic switch gear to isolate faulty equipment’s from the system as quickly as possible.
Protective relay functions are association with the switch gear to avert the consequences or faults. The switch gear must be capable of interrupting both normal currents as well as fault currents. The protective relay on the other hand must be able to recognize an abnormal condition in the power system and take suitable steps to ensure its removal with least possible disturbance to normal operation. It is also overcurrent relay types.

Hence it is the overcurrent relay typesif you will find any incorrect above please comment below in comment box.


For knowing more about overcurrent relay types you must watch this video.

Post a Comment