The large amounts of capital invested in the power systems justify the importance of a reliable protective system. Protection is the art or science of detecting the presence of a fault and initiating the correct tripping of the circuit breakers (C.B). Importance of protection could be understood when a fault (or any other abnormal condition) arises in an electrical power system. That fault must be isolated as quickly as possible from all live supplies in order to:
· Retain system stability, (to keep all generators running in synchronism).
· Reduce the damage both at the point of fault, due to fire and explosion, and in the parts of the system carrying the fault current, due to over heating.
The protective system should have the following characteristics:
· sensitive to all types of faults
· reliable
· fast acting
· economical
· selective and discriminative
Selectivity of the protective scheme means that only the faulty section should be isolated from the rest of the system which in turn means that the healthy parts of the system should be unaffected by the protective scheme.
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