DEVELOPMENT AND RESULTS OF A WORLDWIDE TRANSFORMER RELIABILITY SURVEY

To date, the only major international survey on large power transformer failures was published in 1983. Since then, the results of this survey have become an international benchmark in the transformer industry for the performance of transformers, in particular the failure rate. In 2008, Cigré Working Group A2.37 Transformer Reliability was formed with the following objectives:  - Reviewing all existing surveys and study different practices (in terms of data collection, compilation, etc.)  - Conducting a new international survey on transformer failures  - Compiling and analysing the collected data, and interpreting the results (calculation of failure rates, classification into failure location, failure causes and failure modes. In this contribution the data collection methodology developed by Working Group A2.37 is described, and a uniform way of collecting, compiling and presenting data is proposed. The results and analysis of the new international transformer failure survey are presented in terms of the investigated population, calculated failure rates and failures classification into location, cause, mode and effects of the failures. The working group has collected 964 major failures which occurred in the period 1996 to 2010, within a total population of 167, 459 transformer-years, contributed by 58 utilities from 21 countries. The year of manufacture of the units span from the 1950’s up to 2009. The failure rate of substation, generator step-up and the combined group of transformers were all within 1%. Winding related failures appeared to be the largest contributor of major failures, irrespective of transformer application or manufacturing period, and due to their impact typically led to a situation where the failed transformer was scrapped. Failures originating in the bushings most often lead to severe consequences such as fires and explosions. Dielectric mode failures were the highest contributor to failure modes, irrespective of transformer application.