Identification of partial discharges in power transformers: An approach driven by practical experience

High voltage power transformers are the most challenging equipment for asset managers in that their failures are often due to thermal, electrical, ambient, and mechanical stresses that interact in a synergic way. An accurate failure mode analysis is often prevented by the compound nature of the insulation (partly solid, partly liquid, self-regenerative, and highly flammable) and by the high probability that failures involve explosions. Insulation failure is, by far, the costlier event with an average cost of about $150,000 (1999) per outage [1]. Therefore, it is worthwhile to understand better the symptoms that indicate an imminent failure. The aim of this article is to provide practical information for partial discharge source identification for oil-immersed transformers. The features of some common manufacturing defects rarely discussed in the literature are presented. Creeping discharges are also investigated through a setup intended to improve partial discharge identification.