Distribution transformers: A study of the relationship of their oil dielectric strength and their previous history

This paper is concerned with the correlation of the oil dielectric strength and the previous history of a number of distribution transformers of the P. P. C. (Public Power Corporation) from the region of Eastern Macedonia and Thrace. Our samples come from distribution transformers from the Xanthi area and from the broader region of Macedonia and Thrace, Northern Greece. In the Xanthi area there are 1631 distribution transformers. In the broader region of Macedonia and Thrace 39963 distribution transformers are in the network. Our work is a continuation of the work reported in CIRED 2001. Our 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.