CONCEPTS OF PROTECTIVE DEVICES

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 current flow through it & they break the ckt. The fuse element generally made of materials having low melting point & high conductivity.

Relay

Protective relay is a device that detects  fault & initiates the operation of the ckt breaker to isolate the detective element from the rest of the system.

                                         

Circuit breakers

A ckt breakers is a piece of equipment which can,

• Make or break a ckt either manually or remote control under normal condition.
• Break a ckt automatically under faulty condition.
• Make a ckt either manually or by remote control under fault condition.

Lighting arrestor

A Lighting arrestor or surge diverter is a protective device which conducts the high voltage surge on the power system to the ground.

Isolator

Isolator is a disconnecting switch which operates under no load condition. It has no any specified current breaking capacity or current making capacity. Isolator is not even used for breaking load current.

Current limiting reactor

A reactor is a coil of no. of turns designed to have a large inductance as compared to its ohmic resistance. which limit the short ckt current to a value which the ckt breakers can be bundle , additional reactance known as reactors are connected in series with the system at suitable point.

Insulator

Insulator provides necessary insulation between line & supports & thus prevent any leakage current from conductors do not flow to earth supports line current must be properly insulated from supports.