Further statistically analyzed results of measurements of the dielectric strength of oil in distribution transformers

This paper is concerned with the correlation of the oil dielectric strength and the previous history of a number of distribution transformers of the Greek PPC (Public Power Corporation) from the region of Macedonia and Thrace. The authors´ samples come from distribution transformers from the Xanthi area and from the broader region of Macedonia and Thrace. In the Xanthi area, there are 1481 distribution transformers. In the broader region of Macedonia and Thrace, 36158 distribution transformers are in the network. Their work is a continuation of the work reported in CIRED 1999. Their effort is concentrated on the establishment of a statistical model which would relate the dielectric strength with the electric stresses to which a distribution transformer is subjected as well as its previous history. It is to be noted that the measurements of the dielectric strength were carried out with the aid of a Foster test cell according to the BS 148/78 standard