Study on the dynamic mechanical properties of winding-block axial structure considering short circuit strain rate effect

Transformers may suffer multiple short-circuit impacts during long-term operation, and axial instability is one of the typical types of serious accidents caused by short-circuit faults. The axial instability form of the winding-block structure is analysed, and the dynamic solution of the winding short-circuit electromagnetic force is obtained by establishing the three-dimensional magnetic-circuit-force multi-physical field coupling simulation model. The influence of strain rate on the cushion block constitutive equation is corrected, and the modified model is verified by short-circuit impact test and quasi-static test. The research results show that for 110 kV 31.5 MVA transformers, the maximum electromagnetic axial resultant force of winding is 363.16 kN, and the ultimate tilt force is 1214.2 kN. The pre-tightening force configuration is accordingly recommended to range from 363.16 to 608.28 kN, which is narrowed by 18.49% compared with the static calculation method; Meanwhile, adding a logarithmic strain rate correction term to the classical constitutive equation of the cushion block can achieve a good correction of the stress-strain relationship with the coefficient of determination above 0.99, and the cushion block has a larger elastic modulus under high strain rate load. The research results provide an important theoretical reference for the axial stability structure of transformers.