Effects of electric arc on the dielectric properties, partial discharge patterns and dissolved gases in silicone oil

Transformers are widely used as key high voltage equipments in an electric power system. Insulations play important roles in maintaining the high voltage transformers to perform normally. Silicone oil is among liquid insulating materials used as a transformers insulating liquid. It performs as an insulating and cooling liquid. An electrical arc may occur when a particular extreme condition happen in operating transformer. Electrical arc is a very dangerous since it has high energy and it might increase the liquid temperature. This paper reports the effect of electrical arc to dielectric characteristics, partial discharge patterns and dissolved gas in the silicone liquid. The electrical arc was generated using multi needles-plane electrode system under AC applied voltage of 12 kV, 20 kV and 24 kV. The arc parameters used were duration (0, 5, 10 and 15 minute) and magnitude indicated by the applied voltage. The combination between the duration and magnitude represents the arc energy. Experimental results indicated that electrical arc reduced the breakdown voltages, relative permittivity, resistivity and inception voltage of partial discharges. The reduction increased as larger arc was used in longer duration. Electrical arc increased the value of dielectric loss factor (tan δ). The electrical arc promoted the dissolved gases, including combustible gases. Acetylene (C₂H₂) had the highest concentration among the combustible gases produced. These results indicated that electrical arc reduced the overall performances of the silicone oil significantly. Therefore, it is important to avoid an electrical arc to occur in silicone insulating liquid to keep the integrity of its performances.