Bus and Breaker Fail Protection for Industrial and Commercial Power Systems Part II: Breaker Fail Protection and Conclusion Working Group Report

This paper discusses bus and breaker fail protection in modern industrial and commercial power systems. Fault current levels are increasing due to increases in power transmission system capacities and in-plant power generation. Such high fault currents as well as in-plant generator dynamics and system arc flash incident energy limiting requirements necessitate fast bus fault clearing. Meanwhile advancements of numerical relays proved more appealing economically and technically for MV and LV bus protection applications. On the other hand, when bus and breaker fail protection operate, the interrupted segment of the system is larger than a single feeder protection's operation. Consequently, mal-operations of either bus or breaker fail protection are less tolerable than mal-operations of single feeder schemes. This paper is intended to aid protection engineers in making decisions; first if dedicated fast bus and breaker fail protection schemes are required and second what concerns need to be addressed during the selection and the design of such systems. The topics are presented in two separate parts. Part 1 covers scope, introduction and bus protection topics. Part 2 covers breaker fail protection concepts, conclusions and bibliography of additional reference material.