Temperature gradient effect on the space charge behaviour in multilayers of oil and pressboard

The presence of space charge within oil and pressboard (PB) can lead to distortion of electric field within converter transformers. Electric field distortion can cause materials to be overstressed which accelerates degradation, and can result in breakdown. Therefore, it is important to analyse the factors that affect space charge formation and dissipation such as temperature, moisture, ageing, multilayers and electric fields. This paper focuses on the temperature gradient and multilayers of oil and PB on space charge. Considering the inhomogeneous acoustic wave velocity caused by a temperature gradient and different dielectric properties of multilayers of materials, an improved space charge recovery algorithm has been developed, in which the distortion of the acoustic wave caused by the attenuation, dispersion, different dielectric properties and temperature effects have been considered. It has been found that for two layers consisting of PB and oil with the bottom electrode fixed at 20 °C, the electric field in the oil increases under the temperature gradient while decreases at ambient temperature. For a three layered sample consisting of PB, oil, and PB with the bottom electrode at ambient temperature, the electric field gradient exists under the temperature gradient and the maximum electric field occurs near the cathode while occurs near the anode at ambient temperature.