The degradation of insulation systems in high voltage equipment are usually associated with partial discharges, it is therefore necessary to detect, locate and limit partial discharges in order to maintain the insulation quality and thereby protect the equipment from premature failure. Under high temperature, the thermal ageing of transformer insulation accelerates, however the effects of temperature on partial discharges in transformer insulation are unknown. This paper described investigations of the temperature effects on partial discharges. Three insulation defect models, floating objects in oil, surface and oil discharges, were tested at varying temperature levels from 23°C to 70°C. Discharge waveform, amplitude and distribution along the power cycle for each insulation defect model under the temperature of 40°C to 70°C was analysed. The analysis indicates that temperature has no major effects on the waveshape, duration and frequency spectra of floating and surface discharges. Magnitude of floating discharge increases when the temperature is increased, while magnitude of surface discharge decreases when the temperature is increased. Temperature has considerable effects on the magnitude of oil discharges.
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