Investigation for standardization of electrostatic charging tendency measurement of transformer oil in Japan

Several methods for the measurement of electrostatic charging tendency (ECT) of transformer oils were developed in Japan after the streaming electrification phenomena was confirmed. The demand for standardization of the measurement has been raised because of the differences of the methods of measurement and evaluation of ECT. Also many types of measuring apparatus developed up to now have been evaluated for standardization of measuring methods at CIGRE. In the preliminary draft published recently it was concluded that the Mini-static Test is suitable for standardization with high reproducibility and repeatability. However, the ECT value obtained by a Mini-static Tester is often influenced by oil flow rate and varies largely even when using filters from the same lot. Recent investigation showed that the negative dependence of ECT on oil flow rate is caused by the property of the paper filter. The Mini-static Test was recommended as the standard method of ECT measurement although one needs to take a little care of the property of the paper filter in the report by Electric Technology Research Association (ETRA).