Lessons learned from generator tripping events at industrial facilities

This paper relates a number of generator tripping events that occurred within industrial plants in the hope that the ldquolessons learnedrdquo will help others avoid the events described. In many cases, these failures involved human errors and could have been avoided with proper generator protection or personnel training. In a number of cases, plant operators contributed or caused the events. These events were captured on oscillographs. The paper discusses the subtleties of analyzing generator non-fault events such as loss-of-field as well as the important role that sequence of event and oscillographic records play in analyzing these events. The paper also discusses the need to change the established practice of low-resistance grounding (200-400 A) of medium voltage industrial generators. In-service failures indicate the need to limit generator ground current to much lower levels to avoid catastrophic damage. The use of hybrid generator grounding is proposed as a solution to this problem.