CONCEPTS OF PROTECTIVE DEVICES During the operation of power system it is often desirable & necessary to switch on off & protective the various ckt under both normal & abnormal condition. In earlier days this function is completed by using several switch & protective devices. When a fault occurs on any part of the power system, it must be quickly detected & disconnected from this system. The detection of a fault & disconnection of a faulty section or apparatus can be achieved by using fuse or relays in conjunction with ckt breaker. The protective device has been developed in various forms. At the fault a large current flow though the ckt. This large current is damage the ckt equipment & switching device. In order to avoid such damage every part of the power system is provided with a protective relaying system Short description of the protective devices of the system is given below : Fuse A fuse is a short piece of metal when excessive cu