Proposed Methods to Determine Fault Point<tex>$X/R$</tex>Ratio for Breaker Evaluation

Abstract

ANSI/IEEE and IEC standards provide procedures that do a fairly good job in obtaining a single fault point X/R ratio that will allow a conservative estimate of the dc component and, therefore, the total fault current flowing in a breaker. However, there are circuit configurations that result in overly conservative or under conservative estimates of the fault X/R ratio. This paper explores alternate methods using the information in a complex impedance network reduction and presents an alternate method that provides comparable X/R ratios and conservatism without the need to preform dual network reductions.