Influence of water contents on ester liquids partial discharge inception voltage

Partial Discharge Inception Voltage (PDIV) and AC breakdown voltage in insulating liquids are important indicators used for representing their integrity. The test procedures for the determination of these indicators are described in IEC TR 61294 (Determination of the Partial Discharge Inception Voltage) and IEC 60156 'Determination of the breakdown voltage at power frequency - Test method' respectively. In this paper, PDIV and Partial Discharge (PD) activities in a mineral oil, a natural ester and a synthetic ester are considered, taking also into account the influence of added water in these insulating liquids. Furthermore, different PDIV determination criteria have been adopted and compared with the actual described in IEC TR 61294.