Studies in lightning protection on 4000-volt circuits — II

The paper continues the investigations described by the author in another paper on the same subject presented before the Institute in June, 1916 which had for its primary object the reconciliation of the differences between laboratory experiments and experience in service. In the paper an endeavor is made to list the several factors which affect lightning arrester performance and to describe the methods of eliminating these several variables so as to permit the presentation of curves which show the relative merits of the arresters under investigation. The elimination of the several variable factors was accomplished by placing the arresters under practically identical conditions so that no type was at any material advantage or disadvantage on account of the preponderance of the factors which would affect its performance. This was found to be possible for all of the factors except the one relating to density of the arresters, that is, the number per square mile, so that the final curves show the performance of the several types of arresters as affected by their density. These results show that four of the types of arresters are practically identical in their protective value and about 60 per cent as efficient as a fifth type, while the results for the sixth type, being limited to a much smaller number of arresters, and a shorter period of time, do not appear to be conclusive.