Research On Field-Circuit Coupled 3D Transient Eddy Current Field And Winding Short-circuit Strength In Large Transformers

The thesis is based on the item of "Research on 3D Transient Eddy Current Fields and Short-circuit Strength of Coils in large Transformers" and the item of "Research on Simulation Techniques of Transformers under Operation and Fault Conditions". After summarizing relevant literatures, transient eddy current fields in large transformers and winding short-circuit strength are studied deeply. A few achievements with values on theory and engineering have been gained and a software package practical in engineering is developed. Referential rules are provided to improve abilities for transformer windings to withstand short-circuit.The thesis consists of three parts. In the first part, the field-circuit coupled problem of 3D eddy current field is studied. Taking different winding connection manners and asymmetric loads into account, the T-T₀-Ω field-circuit coupled model of 3D transient eddy current field for transformers under operation and fault conditions is established. By using the transformer model established, various fault processes under the constraints of network voltage and parameters are calculated and analyzed. Regularities of short-circuit current variation and magnetic field distribution in transformers are studied. Leakage field of a spiral winding is calculated by approximation method considering its special structure.In the second part, short-circuit strengths of transformer windings are studied. Axial vibrations of transformer windings under sudden short-circuit condition are calculated and the effects of misalign between winding magnetic centers on magnetic field, winding short-circuit force and axial vibration of windings. Large deformation, nonlinear theory is used in the calculation of radial stability of transformer windings. The effects of factors as number of spacer block, etc. on winding stability are analyzed. The stability model of an entire spiral winding is established by using beam elements and rod elements, and stability of the entire winding is calculated. The dynamic strength model of a transformer winding is established and is used in calculating and analyzing. According to analyzing results, a few measures are given to ensure short-circuit strength of windings and referential rules are provided for design of transformer windings.In the third part, postprocessing techniques of finite element for electromagnetic field are studied. Aiming to features of finite element for electromagnetic field of transformers , a fast andhigh-grade hidden line removal and displaying method for 3D finite element meshes of transformers is given. .Based on above studies, a software package is developed which can be use to analyze 3D transient eddy current field and winding short-circuit strength for transformers of various voltage classes, capabilities and kinds of structures under operation and fault conditions. The software package is based on windows platform and has good pre and post processing functions.