Experiences with Line Transformers

This paper presents an analysis of the transformer troubles for one year on a system having nearly 15,000 transformers installed. This analysis indicates that about 50 per cent of the troubles traceable to the transformer can be eliminated, with no great expense, by some slight changes in the construction details and some improvements in operating methods. Reference is made to the Standard Specifications for Line Transformers issued by the Bureau of Standards. An experiment on 1600 transformers with the connection board removed or submerged proved that the connection board above oil was responsible for about 60 per cent of the transformer troubles due to lightning. Curves showing the record of burnouts of four different makes of transformers are used as a basis for a discussion of the effect of the value placed on continuous service in the selection of transformers. The results of experiment with improved lightning protection are given, showing how the troubles were reduced by two-thirds. By taking advantage of the results of the two extended experiments, itshould be possible to reduce the troubles due to lightning to about 10 per cent or 20 per cent of the troubles heretofore experienced.