Experience is reported of short-circuit testing of large power transformers during the past 16 years by KEMA in the Netherlands. In total, 174 transformers > 25 MVA participated in the survey. KEMA shows that at initial access to standard IEC short-circuit tests, 24% failed initially in a wide range of power (194 tests, transformers 25 - 440 MVA, 20 – 500 kV tested). No clear single cause for major failures could be identified; instead, a variety of defects was observed, mostly because of the dynamics associated with passage of short-circuit current. It is the author's observation that change in winding impedance due to short-circuit current passage is an excellent indicator for the short-circuit withstand capability. The authors comment on often heard considerations to replace short-circuit testing by design review procedures, mainly because of costs: ¿ "There is no necessity to test because calculation methods are sufficiently adequate". ¿ "There is no necessity to test because service experience with transformers is so good". ¿ "The costs of testing have become prohibitively high and testing takes too much time". ¿ "Short-circuit testing may have a deteriorating influence on the transformer under test". The authors conclude that design review, as the only component of quality assessment of power transformers, is not sufficient since 1/3 of the transformers that failed in service passed design review. No transformer failed in service had been short-circuit tested prior to installation. In addition, it is demonstrated that a major leap in quality improvement could be realised through full-power testing. It is concluded that although statistically every transformer faces several full short-circuits during its life, the current that really occurs at such a full short-circuit current is smaller than the rated short-circuit for which the transformer is designed. In the future, however, this gap will narrow due to more efficient utilisation of the networks and growth of energy consumption. A brief overview is given on test methods and test installations of the author's laboratory.
|Title of host publication||Proceedings of the 19th Conference on the Electric Power Supply Industry (CEPSI 2012), 15-19 October 2012, Bali, Indonesia|
|Publication status||Published - 2012|
|Event||conference; 19th Conference on the Electric Power Supply Industry; 2012-10-14; 2012-10-17 - |
Duration: 14 Oct 2012 → 17 Oct 2012
|Conference||conference; 19th Conference on the Electric Power Supply Industry; 2012-10-14; 2012-10-17|
|Period||14/10/12 → 17/10/12|
|Other||19th Conference on the Electric Power Supply Industry|