Investigations in order to improve the E.C.T. measurement protocol of large power transformer oil

The streaming electrification in oil-immersed transformers is the cause of some failures in all the countries of the world. Thus, it is necessary to have reliable servicing and checking tools in order to perform steady and reproducible measurements. One investigation method consists of studying the oil/pressboard couples [Touchard G., and al. 1999]. Another method consists of improving the protocol used for electric characterization of the oil (mainly the protocol combined with the Ministatic Tester). This paper explains an enhancement of this measurement protocol.