Performance analysis of alternative liquid insulation for transformers

Abstract

Conventionally, mineral oil and cellulose paper are widely used as insulation medium in transformers over the century due to their excellent electrical, chemical, physical and thermal properties. However in recent years, due to the environmental concerns, conventional mineral oil is replaced by Eco - friendly biodegradable natural esters (i.e. vegetable oils). Abnormal operating conditions are liable for accelerated aging of insulation systems and they lead to unexpected failure of transformers. Liquid insulations play a crucial role in evaluating the failure rate of transformers. There is a necessity to perform investigations on thermally aged liquid insulations to evaluate the characteristics of the transformer. This research covers the laboratory-based accelerated thermal aging studies on performance characteristics of mineral oil and natural esters (sunflower oil and rapeseed oil) with various additives like moisture, Antioxidants and nanoparticles. The failure rate of transformer liquid solid insulations are investigated at various selective environmental conditions by considering relative humidity of the air which is a frequently variable environmental factor. For investigation, mineral oil and natural ester like sunflower oil and rapeseed newlineoil are chosen as the liquid insulation system, and kraft paper is chosen as the solid insulation system. Critical parameters of both humidified and unhumidified samples are periodically measured at an interval of 200 hours of aging. Weibull distribution statistics method is used to predict the failure rate of the insulation system with respect to time and relative humidity of the air. From the analysis, it is inferred that the degradation rate of the transformer liquid solid insulation increases with an increase in relative humidity of the air. It is also noted that the mineral oil degrades rapidly when compared with natural esters. newline newline newline