The utilities in Australia are facing difficulty in making meaningful statistical conclusions about the failure modes as the low failure rate along and a lesser number of transformers do not give accurate statistical results. Researchers, therefore, carried out an international survey to produce the mode and probability of failure data. This data may or may not be valid in an Australian context. Data on 630 failures and retirements were collected and then analyzed. It was found that bushings (16% of failures), on-load tap changers (OLTC) (25% of failures), and windings (16% of failures) were the major causes of failure, with ‘other’ also significant (25% of failures). Nearly half of all failures were caused by design, manufacture or materials. 16% of failures were caused by maintenance and 1.2% by operator error.
The desired outcome of this investigation was to ascertain the probability of failure (PoF) for Australian power transformers, how the statistics compare to previous and international studies, and to determine how the proportions of different failures change over the life and condition of the unit. CIGRE reported that, for distribution transformers, the proportion of bushing failures is now less than that of failures caused by insulation. The proportion of insulation failures is higher in distribution transformers than in transmission units (14% vs 3%). OLTC failures have similar proportions in both transmission and distribution transformers (around one-sixth). This could possibly be explained by the usually more stringent condition monitoring that takes place by the transmission utilities.