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Protection & Switch Gear

Role Of Protective Relays in Protecting the system

The power system protection is necessary to provide a continuous supply. Let us see the role of protective relays in protecting the power system.

Each and every part of the power system is protected with the help of protective relays. The protective relay protects the power system by opening and closing the circuit for a certain microsecond. The entire process is automatic and fast.

The protective relay also includes to current transformer, voltage transformer, trip circuits, Secondary circuit, auxiliary relays, and time delay relays.

Functions of protective relay:

1. To remove the component which is behaving abnormally by closing the trip circuit of the circuit breaker or to buzzer an alarm.

2. To provide protection to other parts of the power system and prevent them from getting damaged.

3. To minimize the loss from damage.

4. To improve the system performance and continuity of service.

Also read: Methods of neutral grounding

Zones of Protection:

The circuit breakers are placed in various places to minimize the damage caused by fault current. A single circuit breaker won’t provide effective protection, for the purpose of effective protection ‘n’ number of circuit breakers are placed in different placed. The respective circuit breaker can also be opened and repairing or any maintenance work can be done without switching OFF the supply to the entire part.

A protective zone is a term used when certain elements are protected in a system so, if any fault occurs on that system, the following circuit breaker only opens. The schematic diagram showing various zones of protection is shown in the figure.


The current transformer only decides the boundary of the protective zones. In practice, the zones are overlapped to provide effective protection.

The Dead spot is the term which is used to denote the zone which was unprotected. If a dead spot condition is identified, it should be overlapped to provide secondary protection.

Overlapping can be used to trip all circuit breakers lying within the region, so there won’t be any damage to other elements.

The probability of damage occurring in an overlapped zone is quite low when compared to the normal protection. The Blindspot is a term which is used to denote the area which is unprotected.

Any error or fault occurring the blind spot won’t be protected.

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