Design and Evaluation of a DSP Based Differential Relay of Power Transformer

Abstract

The problem of mal operation of differential protection of power transformer due to the inrush magnetizing current has long considered as a challenging problem. Several types of protection relays have been used to solve the issue (basic relay, percentage relay, multi slop ….). Each of them has its advantage and its limits. In this paper, a Digital differential relay has been developed and simulated. The logic used to distinguish between the inrush current and the internal fault is based on the theory of harmonic analysis. The behavior of the presented relay has been simulated versus various situations (inrush current, internal fault and external fault). The obtained results show that the proposed algorithm provides a good discrimination and a fast action.