A fundamental approach to transformer thermal modeling - Part II: Field verification

This paper has two main objectives. One is to show that the top oil rise thermal model proposed in the companion paper is valid, for a large power transformer in service. The second is to show that there is a convenient way of estimating the parameters without removing the transformer from service. A Manitoba Hydro 250 MVA OFAF transformer was chosen and instrumented with data-gathering equipment. Two twenty-four hour test runs were performed, one in February of 1999 and the other in July of 1999. The most basic parameter to be determined was the rated top oil rise but also found were the top oil time constant and the nonlinearity exponent, commonly given the symbol n. The results are very positive.