Effect of Moisture Content on Temperature Dependence of Partial Discharge Characteristics of Biodegradable Ester Oil

In our previous studies, we have reported that the relative moisture content of biodegradable ester oil increases with increasing temperature and affects the breakdown voltage (BDV). In this paper, we investigated the dependence of partial discharge (PD) characteristics on moisture content and temperature under conditions of high moisture content in biodegradable ester oil (EO). Toward a corona-free transformer that does not generate PD, in this report, basic PD characteristics were obtained for palm fatty acid esters (PFAE) under AC voltage with varying oil temperature and relative moisture content (RMC) using a needle-plate electrode. The results showed that the frequency of PD generation decreased with increasing oil temperature. It was also found that the frequency of PD occurrence increased, and the average charge decreased with increasing moisture content. We believe that the moisture content (MC) in the oil is the weak point of PD. The partial discharge inception voltage (PDIV) was determined from these PD characteristics, and its relationship was investigated by comparing it with the BDV characteristics.