The effect of moisture on partial discharges in dielectric liquids

The effect of moisture on the inception of partial discharges (PD) along a liquid-solid dielectric interface was investigated in an arrangement incorporating a solid dielectric plate between the flat end-faces of two coaxial cylindrical electrodes immersed in transformer oil or hexadecane. PD parameters were evaluated by measurements of light pulses with a sensitive photomultiplier as well as by an electrical method using an RC detector. The investigation has shown that moisture facilitates the production of gas bubbles and increases the intensity of PD, but the phenomenon depends on the amount of water dissolved in the liquid and on the solid-liquid interface conditions.