Transformer Failure Root Cause Analysis and Developing Mitigation Strategies: A Case of Addis Ababa City
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Date
2023-06
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Addis Ababa University
Abstract
The distribution transformer is a critical component of the distribution system that must be very reliable in order to provide consumers with uninterrupted power supply. The failure of a distribution transformer has an impact on the supply system's reliability and power quality. This study aimed at failure root cause analysis and mitigation strategy development for distribution transformer in Addis Ababa. The study addresses 3,825 number of distribution transformers from the year 2020/21 to 2022/23 and the failure rate obtained is 13.4%. The collected data were recorded failure documents, interview and group discussion from Kotebi maintenance centers, Addis Ababa City Administration Electric Utility (AACAEU) and four electric utility districts in Addis Ababa. In the first part, the results of failure analysis are statistically summarized. In second part, the failure modes, effect analysis (FMEA) is used to analyze distribution transformer failure modes, causes, local and end effects of failure. To identify the most critical parts of the transformer, a risk priority number (RPN) is calculated based on the severity labelling, probability of occurrence, and probability of detection. Thus, from FMEA analysis, the most vulnerable parts of distribution transformers that have highest RPN value of 576 is insulation failure due to human related errors as a primary cause and with electrical mode of failure. Other component failure due to operational error and with thermal mode of failure is 512 RPN followed by winding failure, bushing failure and tap changer failure. FMEA leads to the identification of future preventative measures to be implemented to decrease the risk of the transformer by eliminating the causes of failure, thus minimizing the severity and probability of occurrence. The direct and indirect relationship between failure causes and effects of FMEA components are analyzed using causal loop diagram(CLD) and could clearly recognize unseen failure factors and their consequences. The root cause of transformer failure that covers 75% is human related factors, which is the primary source of operational failure causes like overloading, short circuit, internal problem and others. Solving failure of distribution transformers in Addis Ababa, the developed failure mitigation strategy is an asset management system of especially focused on predictive type supervisory control and data acquisition (SCADA) system. This study could fill the identified gaps, which means it has its own contribution to the body of knowledge of failure analysis. Finally, the outcome of this study has been thesis document, strategic solutions to minimize transformer failure and input source for further research.