TRANSFORMER BUSHINGS – FAILURE CASE STUDIES

Abstract

Relationship between bushing failure and transformer failure is discussed and, in regard of that, two bushing failure types are recognized: incipient bushing failure that does not result in transformer damage and terminal bushing failure having transformer failure as a consequence. It can be seen, that without applying the diagnostics, all bushing failures are terminal. Thirteen bushing failures have been analyzed regarding their cause, failure mechanism and consequences. In that sense, the ability and limitation of off line and on line diagnostics are discussed and some improvements are proposed. Some switchyard properties in the aspect of fire protection are indicated and, especially, the possible influence of rigid tubular connections on bushing failures. Beside mentioned design, service, condition diagnostics and other properties of all three condenser types of bushings are described in the paper.