LESSONS LEARNED FROM GENERATOR TRIPPING EVENTS

A number of generator tripping events that occurred within industrial plants in the hope that the lessons learned will help others to avoid the events are discussed. These failures involved human errors and could have been avoided with proper generator protection or personnel training. In-service failures indicate the need to limit generator ground current to much lower levels to avoid catastrophic damage. Operators have also been known to make errors and create abnormal conditions in which tripping to avoid damage is required. When a generator multiphase fault is detected by protective relays, tripping the generator breaker, field breaker, and turbine shuts down the generator. Reducing fault current decay time is very difficult; however, reducing the fault current during the generator coast-down can be done. Many generator tripping events are caused or exacerbated by improper operator action. There is a need to provide adequate training to generator operators so that they respond properly when various relay functions operate to trip a generator.