Analysis of the influence of low-frequency heating on transformer drying – Part 1: Theoretical analysis

Power transformer field drying is becoming a habitual practice because water is damaging for transformer insulation, and its presence increases the probability of unexpected failures. Several drying methods are currently being employed by utilities. Sometimes, the drying achieved is not very effective because it is carried out with insufficient knowledge of the processes involved. To improve the efficiency of the drying process, some kind of transformer heating is used. Some companies use low-frequency heating (LFH) for this purpose. In this paper, the improvement in drying obtained when LFH is applied is analyzed. Simulations have been conducted using theoretical models to predict the real response of the transformer when LFH is applied. Experimental tests have been performed in the laboratory and on a real transformer to quantify the improvement achieved when LFH is applied.

► The improvement accomplished when LFH is applied to transformer drying is analyzed.
► Theoretical analysis, numerical simulations and laboratory tests were performed.
► In a companion paper, a study carried out over a real transformer is presented.
► LFH increase the efficiency of drying, in special in the case of thicker insulation.
► It’s more important the temperature attained in the insulation that the drying method.