Evaluation of dielectric liquids by measurement of their partial discharge characteristics

Measurements of discharge signatures under AC differentiate between various liquids. The signatures are heavily influenced by the condition of the liquid (i.e gas and moisture content). The radius of the needle electrode also determines which types of positive discharges develop. Measurement of light emission is a sensitive alternative to conventional quasi integrating electrical measurement. The risk for breakdown is greatest for the positive discharges. The positive discharges occur at low rates, probably depending on field enhancement at the needle electrode due to negative space-charges from numerous sub-pC negative discharges.