Primary and backup protection in power system pdf

What is the difference between primary protection and back-up protection?

Normally being unit protection, operation of the primary protection will be fast and will result in the minimum amount of the power system being disconnected. Operation of the back-up protection will be, of necessity, slower and will result in a greater proportion of the primary system being lost.

What is back-up overcurrent protection?

Back-up overcurrent protection may then optionally be applied to ensure that two separate protection systems are available during maintenance of one of the primary protection systems. Back-up protection systems should, ideally, be completely separate from the primary systems.

What is 'back-up protection'?

These secondary systems are referred to as ‘back-up protection’. Back-up protection may be considered as either being ‘local’ or ‘remote’. Local back-up protection is achieved by protection which detects an un-cleared primary system fault at its own location and which then trips its own circuit breakers, e.g. time graded overcurrent relays.

Are primary protection and switchgear components associated with backup protection?

Generally, the protection and switchgear components associated with primary protection are not associated with backup protection. There are two types of backup protection, viz., remote backup and local backup. Backup protection situated at the adjacent substation to backup complete primary protection scheme is known as remote backup.

What is remote backup protection?

Remote backup protection consists of relays that are set to respond to faults in the next zone of protection. This type of protection is relatively slow as it should allow time for the primary relaying in that zone to operate. It also may cause interruption to large portions of the electric supply system.

When should remote back-up protection be applied?

The extent and type of back-up protection applied will naturally be related to the failure risks and relative economic importance of the system. For distribution systems where fault clearance times are not critical, time delayed remote back-up protection may be adequate.