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INTERNATIONAL SYMPOSIUM ON NONLINEAR MECHANICS 6th ISNM NSA NIŠ '2003 Faculty of Mechanical Engineering University of Niš 18000 - NIŠ, A. Medvedeva 14 Tel.: (+381 18) 524-915 Coupled Field Problems in Electrical Apparatus Ivan Yatchev Technical University of Sofia Department of Electrical Apparatus 1156 Sofia, Bulgaria E-mail: [email protected] Introduction In order to model and design real devices it is very often necessary to solve coupled field problems. In electrical apparatus, the electromagnetic field is the main one. The coupled problems encountered in electrical apparatus are most often coupling the electromagnetic field with: - thermal field; - electric circuit; - mechanical motion; - stress analysis problems; - fluid dynamics problems. Very often more than one problem has to be considered, e.g., the electric circuit is existing in almost all apparatus. In the present paper, some examples of these problems are considered in more details and some results are presented. Coupled problem electromagnetic field – electric circuit – thermal field A coupled three-dimensional problem of the above mentioned type is considered for electromagnet of an AC contactor. Finite element method has been employed for solving the problem. General-purpose CAD system is employed for the data input. The coupling is performed in indirect way – by successive solutions of the field-circuit and thermal problems. Results are obtained for steady-state. Coupled problem electromagnetic field – electric circuit – mechanical motion A coupled problem electromagnetic field - electric circuit - mechanical motion has been considered and solved for a solenoid actuator. The algorithm for the solution of the problem has been presented. The electromagnetic field has been modelled using finite element method. Non-linearity is handled using NewtonRaphson method. The electromagnetic force is computed with the help of Maxwell stress tensor. Backward Euler method has been used for integration in time of the resulting system of equations. The results obtained are verified experimentally. Coupled problem electromagnetic field – mechanical motion – electric arc rotation A particular coupled problem is considered for rotating arc SF6 circuit breaker. The process of interaction between the magnetic field and the electric arc rotating in fluid during the current interruption has been studied. The finite element method has been employed for the magnetic field and the interaction between the magnetic field and the electric arc taking into account the motion of the moving contact. Results are obtained for magnetic flux density and electromagnetic force, acting on the arc. Conclusion Several coupled problems encountered in electrical apparatus are presented, mainly of electromechanical nature. The solution of coupled problems is of major importance for the adequate modelling and design of electrical apparatus. Although a lot of research efforts have been employed in this area, there are still problems that are open to be solved.