Planning and coordination of relay in distribution system

Abstract

In any power system network, protection should be planned such that protective relays segregate the faulted portion of the network at the earliest. Normally the distribution system protection comprises of both primary relays and backup relays. The entire distribution network is divided into various overlapping zones to ensure complete protection. The essential requirement of protective relays is that they must be capable of differentiating between faulted conditions, normal operating conditions and abnormal operating conditions. At the same time, they must function only for the specific protection for which they are designed, without operating for any normal and short term acceptable abnormal happenings. Hence, during the failure of primary protection, the backup relays provide protection after some specified time interval. Deciding the proper time discrimination for the operation of backup relays decides the quality protection in distribution network. In this paper, a simulation tool is used for the proper operation of backup relays. It is ensured that the relays located in the backup zone, work to isolate the fault, after giving adequate time discrimination for the operation of the primary zone relays if primary relays do not function and clear the fault. It is capable of optimally identifying set of relay settings for both Primary and Back-up Protection. The fault conditions and the protection coordination problem are formulated and simulated in ETAP. The use of Fault Current Limiters (FCL) and the design of Coordination Time Interval (CTI) are discussed in this paper. The distribution network of Surana industries is considered for the analysis.