Investigation of temperature effects on the ageing of paper-oil insulation under repetitive transient voltages

In this work, the effects of temperature over a range of 20 – 100 °C on paper-oil insulation under repetitive transient voltages have been analyzed. The ageing of the paper-oil insulation is measured based on the dielectric frequency response, partial discharge inception voltage, and intensity of discharges. The Luminol™ TRi oil, considering its oxidation stability and negative index for gassing has been selected as test oil to evaluate its applicability as an alternative liquid insulation for transformers facing continuous high-frequency repetitive transient voltages. The results help in understanding the ageing response of turn-to-turn insulation in wind-turbine step-up transformers subjected to repetitive transient voltages at different operating temperatures.