A novel validated solution for lightning and surge protection of distribution transformers

Abstract

This paper proposes an industrial solution (equipment) for lightning and surge protection of distribution transformers. The proposed protection equipment has been installed at 100 distribution transformers (sample) of the Public Power Corporation (PPC) of Greece. The article estimates the future transformer failures, considering two different cases: (a) transformer without the proposed protection system; and (b) transformer equipped with the proposed protection system. Three different methods are used to estimate the future transformer failures without the proposed protection system: Monte Carlo simulation, Poisson statistical distribution, and binomial statistical distribution. These three methods together with the c control chart method are also used in this paper, for the case of transformers equipped with the proposed protection system, to estimate the maximum allowable number of yearly transformer failures in order the proposed protection system to be considered as an effective protection means. Moreover, the article computes the satisfactory sample size of transformers in which the protection system has to be installed in order to be able to obtain statistically reliable results regarding the effectiveness of the proposed protection system. The results show that the proposed method is an excellent means for lightning and surge protection of distribution transformers, since zero transformer failures have been observed so far during the whole period of its operation (29months), in contrast with 8.36 average lightning and surge related failures per year in the same sample of 100 transformers before the installation of the proposed protection equipment.