Correlation Between Transformer Tap-Changer Design and Sulphur Corrosion

Problems associated with sulphur corrosion in electrical insulating fluids-immersed transformers and tap-changers are complex and continuing research. The problems with corrosive sulphur oils have been widely investigated with significant improvements in understanding that have led to better test methods to detect the possible problems and help avoid them. Practical experience shows that sulphur corrosion in transformer tap-changer does not always lead to failure but may cause other problems in service. Practical experience also shows that sulphur corrosion is not merely a problem with the insulation fluids, it is a problem with the complete transformers and tap-changers, linked with the design, construction, materials utilized, and selection of tap-changers. This paper presents three case studies to draw conclusions of general interest from them.