Partial discharges in liquid embedded power electronics: Effects of pressure and liquid nature under negative pulse voltage stress

There is a need to develop pressure tolerant insulation for power electronic converters used for oil exploitation at deep sea environment. This paper presents an experimental investigation of partial discharges (PDs) along a trench between metallization edges on printed circuit boards (PCBs) embedded in different insulating liquid under unipolar negative fast transient voltages using optical PD detection system. The liquids studied are Nytro 10XN mineral oil, Midel 7131 synthetic ester and Galden fluorinated liquid. Midel has the highest PD inception voltage (PDIV) of 22 kV with high PD magnitude and followed by breakdown at 23 kV. Galden has PDIV of 19 kV with low PD magnitude. Nytro has PDIV of 9 kV with PD magnitude that increased gradually till breakdown. Covering the trench with parylene resulted in PDIV that ranges from 18 kV to 20 kV with similar PD magnitude. It is quite clear from the results that the nature of the encapsulation materials has significant effect on the insulation integrity of power electronic modules.