Calculation And Analysis On Leakage Magnetic Field And Short-Circuit Electromagnetic Force In Large Transformers

The leakage magnetic field and short-circuit electromagnetic force of transformer windings are carried on the static analysis with ANSYS magnetic circuit coupling finite element method in the thesis. Then, the short-circuit strength and dynamic characteristic of short-circuit force on windings are calculated and analyzed with the ANSYS'Structural module, and it has achieved some results with practical value.Taking a 110kV transformer with regulating-voltage windings of three-phase duplex windings for example in the thesis, and built the magnetic circuit coupling 1/4 finite element model of one phase when the transformer have three-phase short-circuit on the winding's symmetry structure. Firstly, the leakage magnetic field is calculated when the windings happen the emergent short-circuit. The leakage magnetic flux density distributions at longitudinal altitude of windings are derived. The influence to the distribution of leakage magnetic field due to the regulating-voltage windings is analyzed, and the axial leakage magnetic flux density distribution at latitudinal extent of windings is analyzed too. The transient short-circuit electromagnetic force is calculated and analyzed during three operation conditions such as maximum tap, rated tap and minimum tap.After giving the short-circuit force of all disks, the mechanical stress of windings are analyzed. The disk between two cushion block is equivalent to a beam model both ends fixed in this thesis, and the stress for each disk is calculated on ANSYS finite element method combined with stress formula. Then, the axial mechanical stability of internal and external winding and radial mechanical stability of internal winding are analyzed. In the part of the dynamic force analysis, the transformer's low-voltage windings are equivalent to the "mass-spring-damping" axial vibration model by several concentrated parameter constituted. The influence of windings inherent frequency in the condition of axial pre-pressures is analyzed. The axial displacement of disk and the short-circuit dynamic force along the winding high distribution at the time of maximal short-circuit current are analyzed too, and the thesis discusses influence of short-circuit dynamic force in different pre-pressures.The analytic method and calculation results have certain directive significance to such transformer structure design in the thesis.