Retrofit design of a line-start permanent-magnet synchronous machine

Abstract

Energy resources are under tremendous pressure with society’s ever increasing need for electricity. However, resources are becoming scarce and the effect of our power generation on the environment is cause for concern. The cost of electricity is also increasing and thus the need to reduce energy consumption is apparent. Most electrical energy generated is consumed by electric motors. Most of these motors are induction motors because they are reliable, efficient and durable. Though these motors are highly efficient, there is still room for improvement when the strain on electrical energy is taken into account. Constructing motors with better efficiency can result in a reduction in energy consumption and cost savings to the consumer. One method of increasing a motor’s efficiency is to use permanent magnets in the construction of the motor’s core. Permanent magnets eliminate the excitation losses experienced by induction machines, thereby increasing the motor’s efficiency. A retrofit design is considered because of the ease of manufacturing for motor suppliers and the ability to apply the solution to existing operating induction machines. The prototype will lay the foundation for future optimisation strategies. The optimised design should provide improved efficiency with a minimum effect on the motors already operating in industry. The design process followed uses the design principles for inductions machines and for sizing permanent magnets. The design is then verified through the use of finite element method software packages, FEMM and ANSYS Maxwell®, and validated by performance testing. A comparison is drawn between the calculated results and the results determined from the performance analysis. The retrofit design performed as expected during the testing with some discrepancies in final values attributed to the manufacturing process. However, the efficiency is lower than designed and requires the implementation of machine optimisation strategies.