Date of Award

Spring 1996

Document Type

Thesis - Restricted

Degree Name

Master of Science (MS)


Electrical and Computer Engineering


In the design of ac contactors, accurate prediction of the coupled electromechanical behavior of the device is critical, especially during the first cycle of ac operation. Many methods have been developed to predict the performance of ac contactors so several costly prototypes need not be constructed. The methods can be classified as based on: closed form solutions, finite element techniques, state space models, and permeance computer programs. In this thesis, three approaches to model the coupled behavior of an ac contactor are investigated which make use of the governing electromagnetic and mechanical equations. The first technique uses a two-dimensional finite element modeling approach with a voltage source excitation and coupling to external circuit elements. In addition, the two-dimensional model makes use of coupled structural finite elements to predict the mechanical performance of the ac contactor. The second approach examined in this thesis uses a similar full-fledged three-dimensional finite element modeling approach with a voltage source excitation and coupling to external circuit elements. Also in the three-dimensional finite element model, a coupled electromagnetic and structural finite element solution technique is used. The third approach used to model the ac contactor is based on a coupled finite element-state space environment which is derived from the governing electrical and mechanical equations. The main parameters of the state space model are the coil inductances which are computed from a series of two dimensional finite element field solutions, separate from the first approach mentioned, in conjunction with an energy perturbation technique. Each of the three modeling approaches mentioned here was used to predict the ac contactor performance at three static armature positions. Next, the models were used to predict the performance characteristics of the ac contactor for the motion case. In addition, the simulation results were compared to experimental data for validation.



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