Module 4 : Overcurrent Protection : Earth Fault …

Module 4 : Overcurrent ProtectionLecture 17 : Earth Fault Protection using Overcurrent Relays Objectives In this lecture, we will learnOvercurrent Protection against Earth coordination for Earth Fault for adaptive Relays Earth - Fault relay is used toprotect feeder against faultsinvolving ground. Typically, earthfaults are single line to groundand double line to ground the purpose of setting andcoordination, only single line toground faults are considered. Consider a radial system asshown in fig For a faultnear the source, the maximumfault current for a-g Fault is givenby . If we model the utility system with identical values for all the sequence impedances then, . Thisvalue is identical to the bolted three phase Fault current. If however, ZS0 < ZS1 then the bolted single lineto ground Fault current can be higher than the three phase Fault current. As we move away from thesource, for a bolted Fault , Fault current reduces due to larger feeder impedance contribution to thedenominator.

17.3 Relay Co-ordination for Earth-fault Relay (contd..) Example a) Setting of Relay R1 Since the relay is on secondary side of transformer, our …

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  Early, Fault, Ordination, Overcurrent, Relay co ordination, Fault relay

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