Research On Short-circuit Dynamic Stability Of Power Transformer Windings

The power transformer is an important hub in the power system,and its condit ion will directly affect the stable operation of the whole power grid.The transformer accident statistics show it is the main factor threatening the safe operation of transformer in short-circuit fault,due to its lack of anti-short circuit ability.This paper focuses on Nanjing Power Engineering Design Co.Ltd of major science and technology project "the key technology research of near the substation fault analysis and safe operation".In this paper,the short-circuit dynamic characteristics and stability of large power transformer windings are studied in depth.This paper is divided into three parts:First,the static electromagnetic field and the force characteristic of the power transformer in short circuit are analyzed.In a typical 220 kV power transformer as an example,the two dimensional finite element model of the t ransformer is established in the ANSYS finite element software.Based on the finite element static field method,the internal static leakage magnetic field and the force characteristics of the windings in the normal state of transformer are analyzed,and the influence of different kinds of deformation on the electromagnetic force is also analyzed.Then,the short-circuit strength of the power transformer windings is analyzed.Based on the theory of magnetics-structure coupling field,the characteristics of the leakage magnetic field,the electromagnetic force and the winding coil strength of the winding are analyzed in the actual system short-circuit fault cases,aiming at the maximum peak time of short-circuit current and the whole process of short-circuit fault.According to the whole process of the force and deformation of the windings,the amplitude stability of windings is analyzed.Finally,the short-circuit vibration stability of the power transformer windings is analyzed.Based on the theory of the eq uivalent elastic modulus of material mechanics,an equivalent dynamic vibration finite element model of transformer windings is proposed.Based on the magnetics-structure coupling field method,the short-circuit leakage magnetic field,axial electromagnetic force,dynamic force and vibration characteristics of transformer windings are analyzed.The axial vibration stability of the high and low voltage windings is analyzed respectively.According to the simulation results and the actual engineering situation,the cause of the instability of the transformer winding structure is analyzed.The finite element magnetics-structure direct coupling fie ld method proposed in this paper can be used to accurately analyze the dynamic response of transformer under the mutual influence of the magnetic field and the structural fie ld.This method is universal in solving the force analysis and stability of actual transformer windings.It also provides theoretical support and guidance for optimizing the transformer winding structure and designing the on-line monitoring scheme of winding deformation.