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

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