Excitation curves of ultra-high-voltage-transformers under conditions of deep saturation are difficult to obtain accurately. In addition, it is difficult to directly measure the remanence of the transformer cores after de-energizing. In this paper researches are made on the above problems. By theory analysis, changes of flux linkage are calculated during energizing and de-energizing processes of transformers. The flux linkage coupling, caused by electric connection of tertiary windings of single phase transformers, is proposed. Methods are proposed to obtain excitation curves and remanences by energizing and de-energizing tests. Results of simulations and experiments show that excitation curve of the transformers under conditions of deep saturation can be corrected by above method, and the remanence after de-energizing can be estimated accurately, thus a good practicability is found for the proposed methods.
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