Vibration Model of Operating Transformer Windings Considering the Dynamic Stiffness

The transformer is the key equipment in the power system, and the winding is the core component of the transformer. Mechanical structure deterioration, such as clamping force loosening, will reduce the short-circuit withstand capability of windings, which will further cause winding damage. Compared with the traditional short-circuit impedance method and frequency response method, vibration-based transformer fault diagnosis method can perform online monitoring of transformer condition. In this study, based on the nonlinear relationship between stress and strain of pressboards under electromagnetic force excitation, a nonlinear MDOF vibration model of windings is established, which takes into account the dynamic stiffness, and the Newmark-β method is used to calculate the time-domain vibration of each winding under different clamping forces. The results show that the vibration of the looseness windings has obvious nonlinear characteristics, and the winding model with dynamic stiffness can accurately reflect the relationship between the nonlinear characteristics and the clamping force.