Evaluation and Analysis of Frequency of Transformer Failures

Abstract

The frequency of failed distribution transformers in Power Holding Company of Nigeria Plc, Akpakpava Business Unit network, Benin City, for a period of two years have been investigated in this work. The frequent power outages recorded in our communities resulting in customers dissatisfactions, economic losses, frustration, complains and demonstrations and wanton destruction of government properties call for concern and investigation. Transformers that dropped J&P fuses causing electric power supply interruption were tested to ascertain if the incipient or thorough fault that must have resulted in open-circuit or short-circuit fault current flowing through the device has damaged it so as not to reclose on fault which could be catastrophic. Logbooks containing complains at the different service units dispatch office were used for the study. The study revealed that in 2005, out of the 390 transformers in the network on load, 26 representing 6.67% failed, while in 2006 out of the 460 transformers in the network on load, 28 representing 6.10% failed the essential tests conducted and so they could not be energized to restore power to the customers connected to them. On opening the failed transformers to ascertain the level of damage, 53 representing 99.00% of the total 54
transformers that failed in the period under review had burnt-coils, while the remaining 1 representing 1.00% had burnt tap changer. The work also revealed that 30 representing 56.00 % of the failed transformers were operating in the wear-out period of their useful-life, 10 representing 19.00% of the failed transformers had no name plate, while the remaining 14 representing 26.00% failed in their useful life period. Since the transformers failed the essential tests the insulating medium (i.e., oil) were not tested in all the cases to ascertain the degrading level of its dielectric strength. The investigation also showed that the failure rates fell within the failure rates accepted in developing nations in the world.

Keywords: Practical Transformers, Frequency of Failure, Failed Transformer, Power Supply, Failure Rate, Stress, Losses, and Reliability.