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Analysis of Electric Field Stress and Dielectric Loss in Insulation of Magnetic Component for Cascaded Power Electronic Transformer

In this paper, the voltage, electric field, and dielectric loss of the high frequency transformer used in power electronic transformer are studied. According to the finite element method (FEM), the influence of the voltage and harmonic components on the electric field distribution and dielectric loss of the high frequency transformer were calculated. The results show that the voltage of high frequency transformer winding to the ground is greater than that of winding terminal voltage at the top module of the cascade structure. Moreover, the former voltage contains lots of high order harmonics. The insulation between the windings suffers from the nonsinusoidal periodic voltages with multi-harmonics. The superposition of the harmonic stresses enhances the electric field distortion in the insulation, which probably causes partial discharges and insulation failure. The electric field respect to the high voltage winding to the ground with harmonics presents high values at the end of the windings and between the turns. The dielectric losses of the insulation under the high-frequency field are much higher than that of power frequency (50 Hz). It is mainly caused by the switching frequency and the high electric field. This work is of great significance to the insulation design of high voltage and large capacity power electronic transformer.