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Electric Machine Design using SPEED and Motor-CAD
repeatedly and questioningly to the examples one encounters in the course of one’s work as a designer.
Guiding principles
The design engineer is thus faced with rules of thumb that don’t always work, and equations that may be applicable only in special cases. Nowadays s/he is also faced with software that may require a considerable learning period, making the overall learning process even more complicated. Additional complexities can arise because of interactions with power-electronics, control, protection, heat transfer, failure modes, manufacturability, production issues, material properties, costs, and many other factors.
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Collect rules of thumb. Only experience will tell whether or not they are reliable. Some rules of thumb may yield their secrets to scientific analysis; but others will defy analysis, and in such cases they may be risky. They must necessarily be broken in many cases, but with scientific justification or experimental proof when this is possible.
What guidance can be given to design engineers (especially young design engineers) facing these complex challenges? The authors can do no more than offer a few points of advice based on their own experience, which covers 45 years of engagement in industrial companies and in the SPEED laboratory:
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Measure and test everything in the lab. Spend as much time as possible on the factory floor.
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Keep in shape. Do lots of practice. Read a lot. Study. Keep asking questions.
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SPEED and Motor-CAD
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Keep company with experienced engineers. This is by far the most valuable external source of wisdom and know-how. While personal experience and initiative is also important, no-one can encompass the subject alone, and “only a fool learns by his own mistakes”.1 Keep a firm grip on the fundamental physical principles such as Faraday’s law, and many others. In the authors' experience it seems that the top engineers always have an unshakeable grasp of the basics. They are rarely the ones who use sophisticated theories. They seem to be characteristically skilled in dealing with a mosaic of interacting factors, while being able to see the essential physical laws at work behind them. Often when something isn’t right, they will notice a conflict with one of the essential physical laws. For example, when one thing goes up, another goes down (especially when it shouldn’t). Such observations appear to be based on an almost intuitive grasp of the essential physical laws. But these laws are not actually intuitive. For centuries, great minds were frustrated searching for the “simple” laws of mechanics and electromagnetism. Therefore it is necessary to learn them, and to go on learning them, by applying them
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This maxim should be relaxed for engineers. “Nothing ventured, nothing gained”.
SPEED and Motor-CAD are designed to help engineers who follow these principles. They collect many of the methods and calculations that designers do every day. These calculations are commonly done thousands of times during a design exercise, as different combinations of dimensions and parameters are changed in the search for an “optimum” design or even one that simply meets the requirements. For this reason SPEED and Motor-CAD are designed to be fast. Primarily one should think of SPEED and MotorCAD as a numerical and theoretical companion. In skilled hands, SPEED and Motor-CAD are capable of accurate and sophisticated design calculations. Both programs are primarily analytical, supported by PC-FEA for 2dimensional magnetostatic and thermal calculations. They can be used in conjunction with other specialist software — for example, FLUX™ for finite-element analysis, or STARCCM+™ for fluid flow. SPEED and Motor-CAD can be used for selflearning about electric machines, or as a tool in the teaching of electric machine performance and design. Until the publication of this book, the use of SPEED and Motor-CAD for these educational purposes was not documented, so this book is intended as a “grand tutorial” for most of the basic steps. Of course, much more can be found in the extensive internal documentation and the theory references and books.