Reliability analysis of premature failed 11/0.433kV hermetically sealed distribution transformers

There were around 450 units of 11/0.433kV distribution transformers which have found to fail prematurely over the past 15 years. These distribution transformers are vital to power utilities as they supply electricity to respective customers in industrial, commercial or domestic areas. Failure of distribution transformers will result in power interruption which not only reduces the utility´s revenue, but also causes loss of customer confidence towards the utility. Hence, it is imperative that power utilities, such as Tenaga Nasional Berhad (TNB) to perform studies to assess the reliability of distribution transformer. The reliability analysis is supported by the internal inspection which was guided by a standardized procedure. This paper presents a reliability analysis method called Life Data Analysis which utilizes statistical distribution, Weibull distribution to analyze and compare the reliability of distribution transformers from 3 different manufacturers. It has been found that the findings of the reliability parameters are consistent with the nature of incipient faults in the transformer.