Feeder Interruptions Caused by Recurring Faults on Distribution Feeders: Faults You Don´t Know About

Weather, equipment failure, and contact by foreign objects cause faults, trips, interruptions, and outages. Most faults are either permanent, requiring repairs before service can be restored, or truly temporary, causing no lasting impairment to the system. Monitoring programs at Texas A&M University have instrumented dozens of feeders at North American utility companies for multiple years. Sensitive monitoring and recording systems have documented multiple instances in which failing apparatus, vegetation intrusion, and other factors have caused multiple faults and momentary interruptions, over significant periods of time, without causing sustained outages. A recurrent fault can easily escape notice when a pole-mount recloser is the interrupting device, because there often is no telemetry (e.g., SCADA) to report that anything happened. Even recurrent faults that trip a substation breaker can escape notice when time intervals between operations are sufficiently long for operator memories to fade. Fault current and arcing from recurrent faults can further damage already weak apparatus, eventually causing a permanent outage, at which time there may be more consequential damage to apparatus, including burned-down lines. This paper documents multiple examples of recurrent faults and interruptions, including their causes and consequences. It also documents other events that cause poor power quality and/or reliability after a significant period in which a degraded condition produces electrical "warning signs." These "warning signs" have always been present on feeders but they could not be used to prevent or mitigate problems because the symptoms previously were unknown or inadequately understood.