Discharge Inception and Breakdown of the Oil-Wedge Type Electrode Model Insulated with GTL Based Dielectric Liquids

The article presents results of studies of inception voltage (Vi) and breakdown voltage (Vb) of the oil-wedge type electrode model tested at standard lightning impulse (LI) voltage of negative polarity. The measurements are intended to compare between each other two sustainable dielectric liquids made in GTL technology namely Diala S4 ZX-I and Diala S5 BD. Both oils fulfil the requirements of the IEC 60296 Ed5, type A (High Grade), can be classified as biodegradable, however S5 BD has a lower viscosity and lower pour point (arctic conditions). The comprehensive measurements are carried out based on registration of light emitted by developing discharges as well as on typical voltage waveform recording. The results show that both liquids tested may be considered as relatively comparable; the differences within specific quantities (Vi and Vb) are statistically negligible. In addition, the spread of data, assessed through standard deviation and shape parameter of Weibull distribution, is also similar for both liquids. The experiment confirmed strongly statistical nature of pre-breakdown and breakdown phenomena in liquids, in the condition of paper/pressboard insulated structure.