Distribution transformer lightning-protection practice — II

TO DETERMINE the relative effectiveness of various methods of protecting distribution transformers from lightning an annual survey of operating companies was initiated in 1934 by the transmission and distribution committee of the Edison Electric Institute and continued through 1935 and 1936. In 1934 operating data were obtained from 38 companies, in 1935 from 43 companies, and in 1936 from 41 companies. The results for 1934 were presented in a previous paper. This paper presents a summary of the data for the three years and draws conclusions therefrom. It is only by collecting such data from a number of companies for numerous installations for a number of years will conclusive data be obtained so that annual variations in storm frequency and severity will be averaged. It is planned to continue the collection of these data for several years. In the future it is hoped that data for a sufficient number of years will be obtained from each company so that the troubles may be weighted by the isokeraunic level of each territory served.