Calculation On The Windings Short-Circuit Electromagnetic Force In Power Transformers

The leakage magnetic field, winding short-circuit force and strength are calculated and analyzed using the finite element method during the single-phase short-circuit in transformer such as three phase five limb transformer in the thesis. A few achievements with values on theory and engineering have been gained, referential rules are provided to improve abilities for transformer winding to withstand short-circuit.The significance and purpose of the calculation of short-circuit strength of the large power transformers are introduced in the beginning of the thesis, and then the development of the leakage magnetic field of the transformer, the short-circuit force, the winding short-circuit strength problem of transformer are discussed. In the part of the calculation of the leakage magnetic field, numerical calculation of the transient axisymmetric magnetic field are set up based on the theory of finite element method and considering the saturation of the silicon sheet and non-sine varieties of the current, during three operation conditions such as maximum tap, rated tap and minimum tap. The distribution of axial magnetic flux density and radial magnetic flux density for disk unit is obtained, and the influence to the distribution of electromagnetic field due to the regulating windings is analyzed. In the part of the calculation of the electromagnetic force, the short-circuit force which is generated by the interactivity of the short-circuit current and leakage magnetic field are dynamic force actually. The transient short-circuit electromagnetic force are calculated by Lorentz during different taps. The distribution of axial short-circuit force and short-circuit force for disk unit is obtained, and the influence to the distribution of short-circuit force due to the imbalance ampere-turn is analyzed. In the part of the calculation of the winding short-circuit strength. Based on conductor ring between two cushion blocks, static radial force is calculated, and the radial mechanical stability for the disk unit of the inner winding is checked. The result indicated that the ability to withstand short-circuit satisfies the request. The method in the thesis can be use to analyze 2-D transient axisymmetric electromagnetic field and winding short-circuit force and short-circuit strength for transformers of various voltage classes, capabilities and kinds of structures under operation and fault conditions.