计及热老化程度的变压器绕组内线圈短路承受能力评估方法

During the service life of transformers, thermal stresses can change the mechanical properties of pressboards, and consequently change windings' withstand ability to short circuits (WASC). In this paper, the accelerated aging experiments were conducted firstly to obtain the mechanical properties of aging pressboards. Secondly, radial bending stresses and critical loads of inner windings were analyzed by establishing the finite element model, where the stiffness of stays was considered. Finally, the proposed model was used to evaluate the WASC of a 110 kV out-of-service power transformer, and short-circuit tests were carried out. The results show that the elastic modulus of pressboards drops with the increasing aging degree. Based on the proposed model, the radial bending stresses and the critical load are one-fifth and a quarter of the results calculated from the beam model and the two-hinged arch model, respectively. With the increasing degree of aging, the safety factor of radial bending stresses increases, while the safety factor of critical load decreases, indicating that the aged windings are easily to have buckling deformation. The conclusions can provide an important basis for evaluating the WASC of aging transformers.