Relay Coordination Algorithm with Limits on Minimum Operating Time of customized Time Inverse Relays Characteristics

Operating time of overcurrent relays is minimized in most of the overcurrent relay coordination studies by minimizing the summation of operating time of the all main overcurrent relays. Nonstandard time inverse overcurrent relay characteristics are further used for minimization of operating time of overcurrent relays in the distribution system where fault current contribution from the distributed energy resources (DER) is extremely weak. In practical, this fast optimized operating time of relay is very hard to realize in field. If this fast operating time is realized in field, then it may cause unwanted tripping of feeders during the network temporary faults. This article discusses a modified relay coordination algorithm in which, a lower limit is provided on the operating time of overcurrent relays to block their operation during the temporary fault periods. In addition to this contribution, the application of the customized time-inverse relay characteristics are also extended for maintaining the relay coordination in distribution system with integration of distributed energy resources.