The influence of oil speed and temperature on PD phenomena in transformer insulation

Identifying partial discharge (PD) phenomena in power transformers is the key to achieve proper maintenance actions. In order to tag a recorded PD pattern obtained from either on site testing or monitoring as, e.g., internal, surface or corona discharges, a diagnostic database has to be built first. This database would contain patterns and relevant statistic parameters recorded in the lab under controlled conditions. One of the limits of this approach is that several factors may influence the PD pattern or the partial discharge inception voltage and, thus, identification procedures. In this paper, focus will be on the effects of both temperature and oil flow velocity on surface PD in a pressboard layer at five different oil speeds and with static oil. Statistical analysis is presented to compare the PDIV values.