Experimental investigation on the role of corrosive sulphur on the development of partial discharges in power transformers

An experimental study of the correlation between paper degradation due to corrosive sulphur and partial discharge (PD) activity has been undertaken, using an innovative sensor for the quantitative evaluation of oil corrosivity and advanced technology for PD measurements. The corrosive sulphur sensor has two active parts which detect different aspects of the oil corrosion process: the first measures directly the corrosion level on the copper, while the second provides the threat level of the byproducts of the copper corrosion. Through accelerated aging of paper wraps in oil where corrosion was induced purposely, the behavior of PD in terms of inception voltage and pattern has been investigated as a function of oil temperature and corrosion extent. The significant variation of the partial discharge inception voltage (PDIV) measured and the type of pattern obtained can be used to devise a diagnostic approach regarding the danger of oil corrosivity based on PD measurements and corrosive sulphur detection.