Fast tripping of utility breakers and industrial load interruptions

Some industries are very sensitive to electric power interruptions and voltage sags, which are a normal consequence of the utility fault-clearing process. Typically, US utilities will try once or twice to clear faults without blowing any tap fuses, which would require dispatching a trouble crew to replace. To reduce complaints and to improve power quality for critical customers with high economic impact of interruptions, some utilities have been eliminating fuse-saving practices on feeder breakers and reclosers. The impact on overall reliability and the number of interruptions is evaluated based on distribution feeder power quality data. Some degradation in overall reliability can be expected, but this can be minimized with judicious placement of line reclosers. Critical customers can expect a significant reduction in the number of interruptions. A value-based economic analysis, including both utility and customer costs, shows that the practice has a high overall benefit-to-cost ratio. The utility experiences increased costs, but these are frequently overshadowed by the potential customer savings. However, removing fast tripping may correct for only a small portion of the utility-related events that might disrupt sensitive industrial processes. This article analyzes the impacts of removing fast tripping on reliability indices and on power system economics.