Design of insulated structure for load-ratio voltage power transformer by finite element method

For improving the insulation level of a 220 kV load-ratio voltage power transformer, two-dimensional and three-dimensional electric fields around the shielding ring of the regulative winding in this transformer have been precisely calculated by the finite element method. The calculated results show that the field intensity at the oil-corner for the shielding ring with the traditional oil-corner design is too high to insure an adequate insulation level for this transformer. Two new shielding ring structures without an oil-corner have been designed by using the finite element method. The maximum field intensity for each new design is reduced to 2.000 kV/mm from 2.633 kV/mm under 100 kV applied voltage.<>