CHAPTER -1                           INTRODUCTION1.1 RadialFeeder ProtectionThe modern age has come to heavily depend upon the continuesand reliable flow of electricity because there are many appliances that needelectricity to carry out their work .Computer and telecommunication networks, industries, railways ,Airports are the few applications that required the continuous andhigh value of electricity to carry out their functions properly. No powersupply in this world is not design in such a way that it’s never fails .

Soprotection is required for the continuous flow of electricity.In power distribution system there are mostly transformer,shunt capacitors banks and protective devices which age over time and themostly the distribution system is over headed which could easily effected bythe weather, animals, etc. As the radial distribution system is characterizedby having only one single path of flow of power from source to consumer end .Sofor continuous flow of power from source to load end a protection scheme isrequired to installed on the whole system of distribution which result in fastand accurate fault detection that could made the 1.

1.0 Protection schemes can be divided into two major types.(i) Unit Scheme(ii) Non unit Scheme (i) Unit Scheme This type of scheme only protects a specific area of thedistribution system, i.e. bus bar, distribution transformer, generators ortransmission line. The unit scheme is totally based on the Kirchhoff’s currentrule which states that the amount of total current entering in an area must beequal to zero. Any deviation from Kirchhoff’s current rule must indicate anabnormal condition. This scheme only respond to fault that occur in a clearlydefined zone and have fixed boundaries.

The Restricted earth fault and Differentialprotection are the certain types of unit scheme protection which mostly applyon the transformer e.g. Earth fault protection is applied on the high voltagesof delta connected power transformer windings.(ii) Non Unit SchemeThis type of scheme is also applied to a specific area ofpower system but it have no fixed boundaries .

This type of scheme can overlap intoother areas and can be used for backup purposes protection. This protectionscheme also measure current but work on inverse time characteristics whichallow the protection nearest to the fault to operate first. The non-unitprotection has following schemes.a)   Distance protectionb)   Time graded over-current protectionc)   Current gradedover-current protection