Assessment of insulation condition of large power transformers by on-site electrical diagnostic methods

This contribution describes an off-line partial discharge (PD) detection technique for large power transformers in the substation environment. It is demonstrated that off-line PD-analysis is one of the most meaningful method to assess the insulation condition of large power transformers. Details of an advanced PD-detection technique and on-site measuring procedure are described and illustrated with practical examples. The interpretation of results from PD-tests needs complementary diagnostic methods, such as dissolved gas-in-oil-analysis or integral dielectric measurements.