On-site diagnosis for cast-resin transformers

Cast-resin power transformers have been widely used for a long time. These transformers have the advantage of easy installation and improved fire behaviour in case of class F1. Climatic and environmental classification tests E2 and C2 show these transformers have a good behaviour under severe operating conditions. Experience shows their good reliability. To improve even more this reliability during operation, an inspection of the transformers may be carried out: on-site partial discharges measurements are a mean to undertake this inspection. These onsite diagnoses could show abnormal situations such as: too stressed operating conditions; too severe installation conditions; and abnormal ageing of the transformer. All these events may create partial discharges. In this case, transformer life-time may be shortened, depending on partial discharge harmfulness