Field Experiences on Oil Ageing Characteristics of Transformer On-Load Tap Changers

On-Ioad tap changer (OLTC), extinguishing arc with oil, is one of the important components of transformer. Combined many years of field experience, physicochemical properties and electrical properties of oil deteriorate under the combined action of electric, thermal and mechanical agitation. Taking the oil for OLTC in 110kV transformers as research object, ageing characteristics of oil in different operation periods, such as water content, breakdown voltage and oil group composition, were studied comparatively. The results show that the decrease of breakdown voltage is determined by the water content in oil, operation time and operation times of OLTC. Furthermore, the low content of aromatic carbon in the oil is also cause the breakdown voltage to decrease obviously, but the change of water content is small. The water content undulates during operation. The leak of sealed for OLTC is the main factor that makes the breakdown voltage and the water content greatly change.