Zone of Protection System:
All the electrical power system works under zone protection and which can be divided in to several zones of protection. Each zone of protection, contains one or more components of a power system in addition to two circuit breakers. When a fault occurs within the boundary of a particular zone, then the protection system responsible for the protection of the zone acts to isolate (by tripping the Circuit Breakers) every equipment within that zone from the rest of the system. Some of the protecting zone has backup protection for their primary protection.
The circuit Breakers are inserted between the component of the zone and the rest of the power system. Thus, the location of the circuit breaker helps to define the boundaries of the zones of protection.
Different neighboring zones of protection are made to overlap each other, which ensure that no part of the power system remains without protection. However, occurrence of the fault with in the overlapped region will initiate a tripping sequence of different circuit breakers so that the minimum necessary to disconnect the faulty element
Overlapping Zone of Power System:
Overlapping Zones are having powerful advantage; If our power system does not contain overlapping in the protective zone means, then the failure occurs in the equipment will not lie in any one of the zones and hence no circuit breaker would be tripped. The fault occurs in the unprotected system will damage the equipment and hence disturb the continuity of the supply.
The fault in the overlapping zones creates the tripping of one or more circuit breaker associated with the zones, in order to isolate the system.
Consider the two protective zone 1 and Zone 2. Here zone 2 overlap the zone1. If there is a fault occurs in the zone 2, the circuit breakers of zone 2 tripped along with the zone 1 circuit breaker. The relay of the zone 2 will also trip the circuit breaker of zone 1 for other faults in the zone 2 which occurs to the right of the circuit breaker. Hence the unnecessary tripping of the breaker can be tolerated only in the particular region.