The Characteristic of Transformer Winding Inter-turn Discharge under Sulphur Corrosion and Thermal Ageing

In order to study transformer winding inter-turn discharge caused by corrosive sulphur, A series of comparative tests were designed. Firstly, a series of accelerated ageing tests of transformer oil were completed. All the oil samples were processed by dehydration and degasification, then divided into three groups, one group samples were added with insulation paper wrapped-copper electrodes and sulphur. while the other group samples were added with electrodes but no sulphur, then aged under 130°C for 14, 24 and 30 days respectively. Next a number of experiments were taken to research the discharge process according to IEC standard methods. The results indicated that the partial discharge inception voltage by corrosive sulfide dropped very significantly compared with the electrodes without sulphur, and it reduced with the ageing time, but the breakdown voltage variation was much smaller and during the whole developing process, the discharge continuing time increased from 14 days to 24 days, then decreased for 24 days to 30 days. At the same time, the insulation papers are taken to measure the tear resistance, which shows the same trend with the discharge continuing time, Those results are valuable for evaluating the transformer condition order of severity corroded by corrosive sulphur and helpful to evaluating the large transformer life and monitoring the condition of large electrical power transformers.