Abstract:On account of the commutation operating conditions of self-shunt excitation transformer, this paper analysed commutation over-voltage that self-shunt excitation transformer took and it's generating mechanism. Meanwhile, this paper studied the ability to withstand over-voltage of self-shunt excitation transformer. Through electric field finite element method to compute electric field that under over-voltage of self-shunt excitation transformer. Finally, this paper provided electric field distribution of self-shunt excitation transformer when controlled rectifier bridge in a deep state, which provided a theoretical basis for insulation design and choice of capacity of self-shunt excitation transformer.