Impact of Aged Pressboard on Space Charge Dynamics in HVDC Transformer Insulation

In this study, the aged pressboard from a failed transformer was used to examine the effect of aged pressboard on charge dynamics. Three types of samples were investigated, including non-aged sample, aged sample, and treated sample of aged pressboard impregnated with new oil. Space charge dynamics of these samples were studied in the presence of a temperature gradient across the sample using a purpose-designed pulsed electroacoustic (PEA) measurement system. Significant effect of aged pressboard on space charge behaviour of the overall insulation system has been observed, even when the impregnated oil was replaced with the fresh oil. It is clear that space charge dynamics of the samples subjected to a temperature gradient were different from those at ambient temperature.