Investigation of Static Electrification Phenomenon due to Transformer Oil Flow in Electric Power Apparatus

Static electrification in oil-insulated systems has been found to be the principal cause of many field failures of large oil-cooled power transformers. In this paper, experimental investigations of the factors affecting the generation and accumulation of static charges due to oil flow in electrical equipment are introduced and discussed. The influence of oil temperature, flow rate, and type and frequency of electrical field energization on streaming electrification of fresh transformer oil (Diala-B) has been investigated by a closed oil cycle. In addition, comparisons between the calculated and the measured values of the relative streaming currents are introduced. A spinning disc system is also used to investigate many factors that can not be easily investigated by the closed cycle used above; e.g. moisture content, antistatic additives, and the material of which the rotating disc is made. The experiments have been carried out for both fresh and aged oil within the temperature range of 20 to 80°C using rotating discs made of various materials. The type of the rotating disc material causes evident quantitative as well as qualitative changes in the measured current. Newly introduced antistatic additives have been used to suppress the electrostatic electrification in flowing oil.