The role of brush spring kinking in a generator flash-over incident

Mechanical analysis and testing of a brush holder and its spring-operated, brush-advancing mechanism revealed a design deficiency in the spring assembly. The deficiency was due to the use of a double-layer constant force spring, which kinked. This design deficiency, in combination with adhesive contamination trapped between the spring layers, lead to mechanical obstruction of the brush travel path. If electrical and mechanical contact with the surface of the generator collector rings is compromised, brush wear accelerates, generating conductive debris. Furthermore, the remaining brushes must carry more electrical current, resulting in localized heating. Both the wear debris, which was allowed to accumulate, and localized heating likely contributed to a destructive flashover in a near-new 230-MW generator.