The correlation between partial discharges (PD) and gassing in insulating liquids

The authors report on investigations performed to determine the relationship between PD parameters and the dissolved gas generated by partial discharges in mineral-based oil. The PD activity of mineral-based oil is shown to depend upon many parameters, including the influence of the standing time between the filling of the test vessel and the switching of the test voltage as well as the voltage´s magnitude on the PD activity. Regarding the gassing behavior, several hydrocarbons show a linear (increasing) dependence upon the integral PD parameters. By contrast the amount of oxygen decreases with increasing PD loading. Calculation of gas ratios indicates that the relation between hydrogen and methane is a sensitive indicator of PD activity in mineral-based oil.