Lessons Learned From Generator Tripping Events

This article relates 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 described. These failures involved human errors and could have been avoided with proper generator protection or personnel training. In many cases, plant operators contributed to or caused the events, which were captured on oscillographs, The subtleties of analyzing generator nonfault events such as loss-of-field as well as the important role that sequence of event and oscillographic records play in analyzing these events are discussed in this article. Also, the need to change the established practice of low-resistance grounding (200- 400 A) of medium-voltage industrial generators is discussed. In-service failures indicate the need to limit generator ground current to much lower levels to avoid catastrophic damage.