Research on nonlinear vibration of transformer winding based on static analysis of axial pressing process

The axial vibration of transformer windings under short-circuit impact is a critical challenge affecting their mechanical stability and operational reliability. Traditional dynamic analysis methods often overlook the prestressed equilibrium state, resulting in significant prediction deviations. To address this issue, this study proposes a coupled static-dynamic framework that integrates nonlinear pad modeling with experimental validation. Static analysis of the axial pressing process revealed that the actual pad stress (1.92 MPa) was significantly lower than the design target (3 MPa) due to the self-weight of the winding, resulting in a non-uniform preload distribution. Dynamic simulations incorporating time-varying electromagnetic forces revealed that the axial displacement amplitude exhibited end-constrained and upper-middle and lower-middle region-enhanced characteristics: the bottom showed the most constraint, while the upper-middle and lower-middle regions exhibited the largest amplitudes. A comparative analysis further demonstrated that insufficient preload caused momentary pad decompression, whereas adequate preload ensured continuous contact and maintained structural stability. The experimental monitoring using fiber Bragg grating sensors qualitatively confirmed the simulated vibration trends, capturing a rapid increase during the initial short-circuit and a secondary surge upon reclosing, despite sensor calibration limitations. Moreover, successive short-circuit events with short intervals led to stress accumulation, highlighting the importance of protection coordination. Overall, the proposed framework enhances vibration prediction accuracy and offers practical guidance for optimizing preload levels, pad layout, and protection strategies to improve transformer short-circuit withstand capability.