Microcomputer based digital differential relaying for generator protection: Real time test results

Abstract

The paper presents the development of a digital differential relaying scheme around a 16-bit microprocessor for generator winding protection. It uses a simple filter algorithm which is based on cross-correlation with a heptagonal wave for the extraction of fundamental frequency components of differential and sum currents. Application of this filter and use of the real parts alone, instead of both the real and imaginary parts, of the fundamental frequency components for the relaying reduces the computation requirement drastically, thus enabling implementation of a complete three-phase differential relay on a single microprocessor without requiring a coprocessor or multiplier. The relay has been tested in real time on simulated generator currents representing internal-, external- and no-fault conditions separately. The test results agree well with the results of off-line evaluation reported earlier and point to a successful implementation of the differential relaying algorithm on a microprocessor in real time.