Method of three-dimensional network solution of leakage field of three-phase transformers

A fast, handy method of assessment of a three-dimensional leakage field distribution and hot-spot localization in three-phase power transformers is proposed. The computational model is based on the reluctance network method. A 3-D leakage field of a three-phase transformer is simulated with an equivalent reluctance of a 3-D network which consists of a lumped MMF within the interwinding gap, active reluctances for nonconductive areas, and complex reluctances in conductive parts. The latter ones take into account the reaction of eddy currents, induced in the tank wall and other metal elements. A corresponding program for an IBM PC/AT computer has been developed which allows an interactive analysis to be done in about 15 s for each structure variant. The proposed method can help to analyze and select optimal structures of 3-D screens and shunts, localize hot spots, etc. Accuracy and error problems are also discussed. The computed results were verified experimentally on several model transformers and compared to 2-D computations for large 240-MVA and other transformers