Keynote talk — Design of large electrical machines

Abstract

Summary form only given. In China, there is a 1000 MW thermal power generator in operation. Large electrical machines are popular in power generation. However, large electrical machines are facing more challenges than small ones due to their features. They have high voltage, high current and high losses, which increase design difficulty in control, insulation and cooling. Moreover, the high torque in large machines will introduce challenges in mechanical designs. It's usually costly to manufacture and maintain the large machines due to their high weight and large volumes. As a result, design of large electrical machines is a complicated process. A review of the general design process of large electrical machines is presented. Firstly, the specifications of the machine should be keep in mind, such as working environment, machine type, electromagnetic performances and so on. Then the topology and parameters of the machine should be selected by optimal design. In addition, stator cooling methods, including air and water cooling, and mechanical supporting of rotor and stator, should be carefully designed respectively.In recent years, large permanent magnet (PM) machines are widely used in wind power, ship propulsion, railway traction, etc. As the capacity of electrical machines increases, there are more and more challenges in design of PM machines. When a PM machine is built and tested, it is often found that the test results do not match predictions well. A set of practical design considerations gained from industrial application experiences are presented, which should be considered during design phase, but often ignored by many machine designers. They are categorized into topology, electromagnetic (EM) performance, loss and efficiency. The causes and effects of some issues are analyzed and some solutions are suggested. They can help machine designers to narrow down the gap between design predictions and test results and build large PM machines with expected performance and high reliability. Superconducting direct-drive generators are new candidates for multi-megawatt class wind generators. Superconducting machines are famous for low weight, small size, and high efficiency. Challenges for large superconducting electrical machines are addressed. In order to find out the suitable topology for multi-megawatt-class direct-drive wind turbine generators, various designs of superconducting machines are compared; advantages and disadvantages are discussed; and a few ways to benefit from their advantages are pointed out. Moreover, characteristics of high and low temperature superconducting materials are concluded. At present, as the current cost of low temperature materials is much lower than high temperature materials. In addition, electromagnetic, mechanical and thermal challenges, including magnet design, excitation system, rotor screen, torque tube, cryogenic cooling system etc., are discussed for superconducting machines.