Failure Modes and Effects Analysis to Mitigate Failure of Distribution Transformers in Ethiopia
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Date
2017-02
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AAU
Abstract
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.
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Keywords
Distribution Transformers, Failure Modes and Effects Analysis, Failure Analysis, Oil Natural Air Natural, Analytical Hierarchy Process