Comparison of phase resolved partial discharge patterns in small test samples, bushing specimen and aged transformer bushing

The transformer bushings are one of the key devices in electrical power networks. With time, the electrical insulations in the transformer bushings become aged. One effect of a long time ageing would be due to Partial Discharge (PD) defects. In this work, the phase resolved partial discharge (PRPD) pattern of the defects naturally present in an aged 36 kV Oil Impregnated Paper (OIP) bushing was compared with the PRPD patterns of defects deliberately introduced in simple test samples and in a bushing specimen. The results presented in this paper show that it might be possible to predict the type of the defects in aged transformer bushings through comparing measured PRPD patterns with PRPD patterns from defects deliberately introduced in simple test samples and in bushing specimens.