Question

Discrimination between main and backup protection is provided by the use of relays which are
1. Fact
2. Sensitive
3. Slow
4. None of these

Answer 1

Correct Answer - Option 3 : Slow

Types of Protection:

• The fault occurs on any part of the electric power system, it must be cleared as soon as possible to avoid damage or interference with the rest of the system.
• The protection scheme divided into two-part that is primary protection and back-up protection.

Primary Protection:

• It is the protection scheme that is designed to protect the component parts of the power system.
• The fault occurs on any line, it will be cleared first by its relay and circuit breaker.
• This forms the primary or main protection and serves as the first line of defense.
• The service record of primary relaying is very high with well over ninety percent of all operations being correct.
• Sometimes faults are not cleared by the primary relay system because of trouble within the relay, wiring system, or breaker. Under such conditions, back-up protection used.

Back-up protection:

• It is the second line of defense in case of failure of the primary protection.
• It is designed to operate with sufficient time delay so that primary relaying will be given enough time hence it is slower than primary protection.
• Definite time delay is used in backup protection.