Effects of voltages with high-frequency contents on the transformer insulation properties

This work studies the changes that occur in transformer insulation properties when voltages with steep fronts and high-frequency contents are applied. With a significant growth in the number of wind-farms and solar-plants that use power-electronic-based converters, the problems associated with such voltages on insulation has led to increasing concerns. Distorted voltages accelerate the transformer insulation degradation. Two identical transformers are studied by energizing independently under power frequency sinusoidal and width-modulated pulse trains. The dielectric characteristics of the test objects, like partial discharge activities, insulation resistance, are periodically measured during the ageing process. After a period of 500 hours of testing the dissolved gases are also analyzed. The results for both transformers are compared and discussed.