Dong-Jin Kweon†, Kyo-Sun Koo*, Jung-Wook Woo* and Joo-Sik Kwak*
Abstract – The life of a power transformer is dependent on the life of the cellulose paper, which
influenced by the hot spot temperature. Thus, the determination of the cellulose paper’s life requires
identifying the hot spot temperature of the transformer. Currently, however, the power transformer
uses a heat run test is used in the factory test to measure top liquid temperature rise and average
winding temperature rise, which is specified in its specification. The hot spot temperature is calculated
by the winding resistance detected during the heat run test. This paper measures the hot spot
temperature in the single-phase, 154kV, 15/20MVA power transformer by the optical fiber sensors and
compares the value with the hot spot temperature calculated by the conventional heat run test in the
factory test. To measure the hot spot temperature, ten optical fiber sensors were installed on both the
high and low voltage winding; and the temperature distribution during the heat run test, three
thermocouples were installed. The hot spot temperature shown in the heat run test was 92.6℃ on the
low voltage winding. However, the hot spot temperature as measured by the optical fiber sensor
appeared between turn 2 and turn 3 on the upper side of the low voltage winding, recording 105.9℃.
The hot spot temperature of the low voltage winding as measured by the optical fiber sensor was 13.3℃
higher than the hot spot temperature calculated by the heat run test. Therefore, the hot spot factor (H)
in IEC 60076-2 appeared to be 2.0.
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