Research On The Field-Circuit Coupled Transient Eddy Current Field And The Spiral Winding Axial Current Effect In Large Transformers

In the dissertation, based on the item "spiral winding's axial current effects in large transformers" and overall generalization of relevant literature, the main attention is paid to problems of three dimension transient eddy current field and axial current effects of spiral winding. Overall, profound and systematical study is taken and a few achievements which have theory and engineering value are gained.The thesis consists of three parts. Part one includes Chapter 2. In this part, detail calculation to magnetic field distribution of spiral winding is taken by numerical integral method. To torsional deflection strength of transformer's spiral winding, the effects of axial current to radial magnetic field is analyzed, which offers base to further numerical calculation of transient eddy current field in transformer.Part two includes Chapter 3 and Chapter 4. In this part, the problem of transient eddy current field and relevant technique are studied thoroughly and systematically. The field-circuit coupled mathematical model, which is suit for two dimension field-circuit couple of voltage source confinement and three dimension nonlinear transient eddy current field basing A-V-A method, is derived in detail. By given voltage confinement, sorts of transient procedures of transformer can be simulated. Post processing techniques to electromagnetic field graph are studied and the Painter Algorithm with data preprocessing is given. Relevant theories as suppression of numerical oscillating, general ICCG pointer memory addressing, etc. are studied. Based on what mentioned above, a common, performance complete and flexible engineering software of field-circuit coupled transient eddy current field and graph post processing is developed.Part three include Chapter 5 and Chapter 6. In this part, by applying the model algorithm given in part two and software, space distribution regularity of transient eddy current field to large transformers such as DEP1-240000/500, SEP-720000/500, etc. which have spiral low voltage winding are studied. And transformer's transient procedures produced by power system interferences of sudden short-circuit, asynchronous parallel in, etc. are simulated. Firstly, the torsional deflection of spiral windings in large transformers is deeply and systemically studied. Effects of transformer's structure and material parameters etc. to torsion electromagnetic force are calculated and analyzed, and the distribution regularities of spiral low voltage winding is given. Afew conclusions and some advice to suppress torsional deflection of spiral winding are proposed, which provide valuable reference base to transformer developers and designers.The achievements of the dissertation can promote applications of transient electromagnetic field numerical calculating theory and improve reliability of large transformer products.