A study of failure of pole mounted distribution transformers

This paper reports on the findings of a field study carried out to determine the causes of premature failures of pole mounted distribution transformers installed in mountainous regions of Saudi Arabia that have comparatively high isokauranic level. The study consisted of transformer failure data analysis, field surveys to inspect installation of transformers, protective devices and grounding arrangements and measurements of grounding resistances, and laboratory measurements on new and used transformers as well as on surge arresters. Based on the study, several possible causes were identified as contributory factors for high failure rates. Recommendations were extended both to power utility as well as local transformer manufacturers. With the implementations of these recommendations, the failure incidences reduced significantly. This paper provides a summary of the study and main findings.