Failure Modes and Effects Analysis to Mitigate Failure of Distribution Transformers in Ethiopia

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This study aims to investigate the causes of failure of distribution transformers in Ethiopia as one of the possible causes for the current power interruption and fluctuation in the country. Failure Modes and Effects Analysis (FMEA) is applied to identify modes of failure, the severity of consequences of those failure modes and detectability of the root causes of failures. Analytical Hierarchy Process (AHP) is also applied to enhance the conventional FMEA process in order to improve the ranking of failure causes. In addition failure classification from various perspectives, unstructured interviewing and questionnaires have been used as an adjunct to complete the study. The study addresses 1322 prominent failures in distribution Oil Natural Air Natural (ONAN) transformers from year 2013 to 2016 having a repair lead time of more than 18 days and also transformers that could not be restored to normal operations since they failed. The transformers have voltage level of 15 and 33KV and capacity ranging from 10-315KVA. For the transformers failure analysis covered in this study, the average failure rate is 6%.Failure analysis of prominent failures by sub-systems shows that winding failure constitutes the leading 52.4% of the total failures, analysis of the failures by regions shows that Addis Ababa region registered the highest number of failures followed by central region and north western regions. Further analysis of failures by modes of failure shows that electrical modes of failure constitute the highest modes of failure with 45%. The output of the FMEA worksheet identifies the most vulnerable parts of distribution power transformers in Ethiopia causing entire damage to the transformers. Thus, the major causes of failure of distribution ONAN transformers in Ethiopia as lack of protective devices, inappropriate testing and diagnosis and inefficient Operation and Maintenance followed by unethical practices with theft of oil and vandalism.



Distribution Transformers, Failure Modes and Effects Analysis, Failure Analysis, Oil Natural Air Natural, Analytical Hierarchy Process