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STATISTICAL ANALYSIS OF TEMPERATURE RISE TEST FOR INCREASED ACCURACY ON X- AND Y- EXPONENTS

C.J.G. Spoorenberg ; SGB - Smit Transformers Nijmegen

Sažetak

On a large number ( > 50 ) of identical large power single-phase autotransformers ONAF
temperature rise test have been performed as part of the customer specification. Part of the 24 hour
test is a 125% overload for 8 hours. Based on this data one can statistically evaluate aspects as average
value, standard deviation and correlation on many parameters.
Measurement tolerances have a large influence on the top oil exponent x and the winding
exponent y. The calculation of x and y is determined by the ratio of two temperature differences due to
a load difference, which can result in larger errors than expected.
In two transformers fibre optic ( FO ) sensors were installed in the common winding to measure
the hot-spot, not only during steady state, but also during transient conditions. For ONAF cooling, a step
increase of load takes a relatively long time before the oil flow reaches a steady state, as is described in
the loading guide. The overshoot in the gradient between the hot-spot temperature and the top oil
temperature is demonstrated and can influence the hot-spot gradient exponent z.
Based on the test results and a statistical simulation one can conclude that the normal tolerances
in the temperature- and resistance measurements, result in a large standard deviation in the exponents
x and y. Use of the exponents x and y, based on a heat run of one single transformer, should be handled
with extreme care. In case of doubt, the use of the exponents given in the loading guide result in a safe
margin when determining the overload capabilities of a transformer.

Ključne riječi

Hrčak ID:

198943

URI

https://hrcak.srce.hr/198943

Datum izdavanja:

15.7.2017.

Posjeta: 753 *