| With the development of extra-high voltage (EHV) power grid technology, more andmore high-voltage and large-capacity transformers have been used in power grid. In order toreduce the cost, most of autotransformers are used nowadays. Compared with the traditionaltransformers, the primary and secondary sides of the autotransformers have not only thecoupling of magnetic field but also the connection of the circuit. The performance analysis forthe extra-high voltage autotransformers becomes more complex because of the particularity ofthe structure. Therefore, in this thesis, the electromagnetic problem of EHV autotransformersis studied based on the field-circuit coupled finite element method (FEM). The main contentsis shown as follows:Firstly, based on the Maxwell’s equations and the circuit connection, the2D field-circuitcoupled FEM mathematical model is derived; and then the corresponding discretization formatof the nonlinear field-circuit coupled model is derived for the autotransformer model.Secondly, according to the derivation of the field-circuit coupled mathematical model, thecorresponding FEM calculating program is made by FORTRAN language. In this thesis, anODFS-334MVA/500kV EHV autotransformer is taken as the example. The leakage magneticfield distribution and winding currents are analyzed under the condition of second sideshort-circuited. The proposed mathematical model and the corresponding program are verifiedby results comparison, which are obtain by the presented FEM program and the commercialsoftware.Finally, the three-dimensional (3D) model of the EHV autotransformer is analyzed by thecommercial software MagNet. The leakage magnetic field distribution and the winding currentare solved under the second side short-circuited condition. Furthermore, the effect of magneticshielding parts on oil tank, the pull plate with slotted, and material selection of plate ofpressuring nail on the leakage magnetic field distribution are investigated in this thesis. |
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