An improved method for estimating temperature rise of a bushing loaded above nameplate rating

The authors have developed an accurate but simple method to estimate the temperature rise (referred to as "rise" hereafter) of a bushing conductor under any load condition. This method consists of one equation and two predetermined rise profiles F/sub 1/(z) and F/sub 2/(z). F/sub 1/(z) is the incremental rise profile at the rated current and F/sub 2/(z) is the normalized rise profile at zero current. F/sub 1/(z) and F/sub 2/(z) can be obtained from two base thermal tests. The proposed method allows estimation of the rise profile of the bushing under any given load condition. Therefore the rise and the location of the hottest spot can be determined from this profile. They have successfully applied this method to various bushings, such as bushings with and without oil circulation, bottom connected and draw-lead connected bushings and some special bushings with two conductors. They examined this method with a thermal circuit model and verified that the thermal model supports the new method.