T Sami - Electrical Engineering Institute, Azarbaijan Higher Education and Research Complex, Tabriz, Iran
a.r Ghahramani
j Tayyebi Mamaghani

Transformers are important and expensive elements of a power and distribution systems. Inordinate localized temperature rise, hottest spot temperature (HST), causes rapid thermal degradation of insulation and subsequent thermal breakdown. To prescribe the limits of short-term and long-term loading capability of a transformer, it is necessary to estimate the HST of transformer winding to as high a degree of accuracy as can possibly be made. Over rate temperature rise in a distribution transformer due to load current is known to be the most important factor in causing rapid degradation of its insulation and decides the optimum load catering ability or the load ability of a transformer. The Top Oil Temperature (TOT) and Hottest Spot Temperature (HST) being natural outcome of this process, an accurate estimation of these parameters is of particular importance. IEEE/IEC among others has proposed procedure to estimate the temperatures. In this paper, IEEE standard C57-91 guide is implemented on Tabriz Distribution Electric Co. transformers.

Distribution Transformer, Thermal Stress, HotSpot, Aging, Transformer Life