Abstract
Conference Title: 2017 70th Annual Conference for Protective Relay Engineers (CPRE) Conference Start Date: 2017, April 3 Conference End Date: 2017, April 6 Conference Location: College Station, TX, USA The work horse of low-impedance bus differential protection is the restrained percent differential element but many modern microprocessor relays also include an unrestrained (AKA: high-set or instantaneous) element which, when not properly applied, can cause false trips. In this paper, we explore the advantages and disadvantages of the use of unrestrained low-impedance bus differential protection including a look back at the history of bus differential and the evolution of the unrestrained element. At the end the authors draw conclusions about the applicability of the element and cautions associated with using it.