New DOCR coordination via non-conventional time curves to achieve bounded relay times

Abstract

In this paper, the new coordination of directional overcurrent relays (DOCRs) is presented to obtain expected relay times. The objective of traditional DOCR coordination is to determine the shortest possible relay time, a non-limited minimization is considered. However, a functional dependence between relays is obtained due the sequence of operation between primary and backup functions, resulting in an uncertainty in the relay times. In the proposed method, the DOCRs are delimited in time intervals resulting in bounded coordination times. The conventional coordination criterion is not used hence there are no coordination pairs, since the commitment of each relay is that its time curve complies with the time intervals. This proposal avoids the incertitude in the relay times in the coordination process, very long or very short times that can affect the operation or safety of the electrical network. In the proposed method, the setting of each relay is stand-alone, the design of time curve must guarantee the relay times for each interval considered, non-conventional curves are used in this proposed. The results in the test systems show that the proposed method is feasible, obtaining the desired results.