Reduction in distribution transformer failure rates and nuisanceoutages using improved lightning protection concepts

摘要

This paper presents a case study of an overhead distributionfeeder in a very high keraunic area. The feeder was experiencingapproximately twice the number of lightning caused transformer failuresper year than any other distribution feeder in the area. In an attemptto lower the outage rate and the repair costs, the lightning protectionfor this feeder was studied and a new protection system was installed.This paper discusses the outage history of this feeder and existingtransformer overvoltage protection. It then details the steps that weretaken to improve the protection so acceptable customer service could beachieved. The interruption data results for one year after theprotection changes were implemented are then presented. The results fromthe field trial of the new lightning protection scheme exhibit asignificant improvement in the feeder service reliability. A compilationof teardown data of failed distribution transformers is also presented.The analysis includes failed transformers from the study feeder, andfailed transformers from the same utility, but not part of the feederstudy. The causes of the transformer failures were tabulated. Theresults from the teardowns indicate that a high percentage ofdistribution transformers with interlaced and noninterlaced secondarywindings fail from low-side voltage surges