Considerations for using high-impedance or low-impedance relays for bus differential protection

Abstract

Two drastically different types of differential relays, one with a single set of very high-impedance inputs and another with multiple sets of low-impedance inputs, are available for bus differential protection. Protection engineers often question which type to choose for their bus protection applications. This paper discusses for each type of relay the concepts used, the pros and cons, and the importance that current transformer selection plays in applications.