PROTECTION OF TRANSMISSION SYSTEM

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Importance of Protection

Limit the damage due to short circuits
Often faulted equipment is damaged
Other equipment is also at risk

Well-designed system will use:
Overlapping primary zones of protection
Some form of backup protection


Attributes of Power System Protection

Reliability
Operate dependably and in healthy operating condition when fault conditions occur, even after remaining idle for months or years.

Selectivity
Clearly discriminate between normal and abnormal system condition to avoid unnecessary, false trips.

Sensitivity
Ability to distinguish the fault condition, although the difference between fault and normal condition is small.

Zones of Protection

Characteristics:
Zones are overlapped.

Circuit breakers are located in the overlap regions.

For a fault anywhere in a zone, all circuit breakers in that zone open to isolate the fault.