Abstract
Experience is reported of short-circuit testing of
large power transformers during the past 14 years by
KEMA in the Netherlands. In total, 119 transformers >
25 MVA participated in the survey.
KEMA shows that at initial access to standard IEC
short-circuit tests, 28% failed initially in a wide range of
power (119 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 shortcircuit
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.
Original language | English |
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Title of host publication | Proceedings of the Travek VIIth int. science and technical conference on large power transformers and diagnostic systems, Travek, Moscow, 22-23-06-2010 |
Place of Publication | Moscow, Russia |
Publisher | Travek |
Publication status | Published - 2010 |