Electromagnetic Field Analysis And Validation In Power Transfomers

This subject is concerned with the finite element analysis of 3-D electromagnetic field problems with multi-subregions in large power transformers and the rerification of various available computing methods, the aim of this paper is to build an integrated engineering -oriented analysis system to effectively solve general engineering electromagnetic field, especially, large scale eddy current problems.The complicated eddy current problem has to be divided into some subregions which may be multiply connected and then the different analysis methods can be suitably chosen for modelling the different subregions. For this reason, the paper proposed and performed 3- Deddy current combined analysis method based on the and the Vpotential sets, thus the complementary advantages of analysis methods to be combined can be gained. Moreover, the numerical implementations can be simplified, and the computing cost can be considerably reduced. To strictly examine the combined usage of different potential sets a novel dualized numerical test was proposed and carried out, that is, two simply connected conducting plates of high permeability weredriven by a uniform and time varying magnetic field, the and the potential sets were adopted in the different plates respectively. The test results have shown the oscillatory phenomena of magnetic flux densities and eddy current along the boundary of plate. Fortunately, a penalty-plus factor proposed in the paper may improve successfully the distributions of eddy currents. Besides, the key role of the penalty-plus factor in enhancing the gauging conditions has been confirmed in this paper.A 3-D stray-field loss model which was approved by the international TEAM steering committee as TEAM workshop Problem 21. The problem has been analyzed by the and the codes made by author,and the key techniques of computer-aided-measurement of eddy currents on conducting surface and interlinked magnetic flux at prescribed positions were developed and applied.This paper investigated the numerical approximation problems, involving the distributions of non- zero divergence" with Coulomb gauging in conducting region, the effects of the non-zero divergence" on eddy current solutions and the "discrete" interfacing conditions to be weakly satisfied. The improved interface processings weresuggested. In the approach the En=0 constraint conditions to conductor surface affect strikingly the waveforms of transient eddy currents as well as the uniqueness of eddy current solutions.The method to approach 3-D eddy current problems was investigated to avoid the modelling of complicated structures of field source, and it has been used to model the Problem 21. The special attentions have been paid in dealing with interface, symmetric plane and far field boundary, without making discontinuous on the interface between conducting and non-conducting regions, however, the satisfactory accuracy of calculated by author's code was achieved comparing with the measured results.The standard Galerkin residual elements were given based on various formulations to make easily the 3-D eddy current code in the form of standard modules not with repetition work.Finally, the electromagnetic field applications in power transformers concerning the electromagnetic forces, leakage impedance and eddy current losses analysis to structure parts have been presented in this paper.Doctor student: Cheng Zhiguang(Electric Machine) Directed by Prof. Chen Pizhang, Prof. Ma Xinshan,and associate Prof. Zhang Jishi...