A linear synchronous motor for urban transit using rare-earth magnets

This paper describes a track-powered propulsion system for automated urban transit vehicles. It is a linear synchronous motor which is similar in principle to the motor previously designed for the Canadian 500 km/h Maglev system. The urban vehicle has an array of samarium-cobalt magnets fixed to a backing plate on the underside of the vehicle. These magnets interact with insulated aluminum cables imbedded in the track surface and carrying variable-frequency current supplied from periodically-placed track-side inverter stations. No iron is used in the track. The vehicle is suspended on wheels. The air gap clearance between the vehicle magnets and the track surface is about 40 mm. The paper describes a typical design in which the propulsion system, operating at maximum power output of 240 kW, has an efficiency of 77% and a power factor of 88%, using inverters with 200 m spacing. The system appears to have excellent technical and control features. Its economy will depend on the future cost of rare-earth magnet material.