A methodology for accurate simulation of movable parts under the influence of electromagnetic forces

Van Staden, Christian Olivier
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Many devices, for example contactors and solenoid actuated valves, rely on ferromagnetic components moving under the influence of electromagnetic force for their operation. The popularity of this technology stems from the fact that it is an elegant, cost effective and robust way to convert electrical energy into mechanical work. From a product design point of view it is very important to quantify the magnitude of the electromagnetic force and to predict the behaviour of ferromagnetic components under the influence of this force. In most cases these forces are estimated by means of first order calculations or Finite Element Methods. It is plausible, as this dissertation shows, that direct measurement can be used to replace or supplement theoretical methods to obtain these forces. However, limited previous work describing methods and techniques for the measurement of these electromagnetic forces, are available in the public domain. In general, prior work in this field [12] is very specialised and limited with respect to the range of forces that can be measured, and not easily adaptable to a product design environment. This thesis proposes a novel piece of equipment for the measurement of electromagnetic forces acting on ferromagnetic components, and a method to predict product performance based on these measurements. The measurement equipment, and product performance prediction, is described and evaluated for the case of low voltage hydraulic magnetic circuit breakers. Low voltage hydraulic magnetic circuit breakers are a particularly interesting subject as it contains one source of electromagnetic force acting on two ferromagnetic components. The two ferromagnetic components have different equations of motion, with dramatically different damping coefficients. A further complication in the operation of hydraulic magnetic circuit breakers is that these ferromagnetic components can move separately or simultaneously. The motion of the components is influenced by the magnitude of the applied electromagnetic force and their position relative to each other. Low voltage hydraulic magnetic circuit breaker performance is subject to the combined motion of these two ferromagnetic components. This work concludes that the method for measuring electromagnetic forces with the aim of predicting device performance is feasible, and that it produces good results where electromagnetic forces need to be known to high accuracies.