Siemens builds a 400kW super motor

Siemens has developed Europe`s first motor to use windings formed from high-temperature superconductors. The motor, built at the company`s Erlangen research centre, has been operated continuously at 400kW in both motor and generator modes.

Because superconductors have no resistance when they are cooled below a critical temperature, motors using superconducting windings have much lower losses than conventional machines and can be far smaller.

Until about 15 years ago, superconducting materials had to be cooled to -273°C to exhibit the effect, and had few practical applications. But the discovery of a new generation of "high-temperature" superconductors (HTSs) which lose resistance below -190°C, made the cooling process much simpler and cheaper and opened up the prospect of compact, low-loss machines based on HTS windings.

Since then, researchers around the world have been trying to develop practical applications for the new materials.

The experimental Siemens motor (shown above) has twice the output of a conventional motor of a similar size. The machine, sponsored by the German Ministry for Education and Research, has a rotor with superconducting coils mounted in a frame with an air-gap stator winding. The rotor is cooled using a closed-circuit system.

As well as offering improved electrical performance, there are also mechanical advantages. The motor can have a smaller rotor than usual, and the iron teeth that carry magnetic flux in conventional motors are not needed. As well as being smaller and lighter, the motor is also said to be quieter than a conventional machine.

Siemens sees the development of the superconducting motor as "a decisive step" on the road to commercialising the technology. It envisages HTS motors finding applications where the small size and high efficiency would be beneficial, such as on board ships and oil platforms. The technology could also be adapted to produce high-speed generators that could be coupled directly to turbines without needing gearboxes.

Although Siemens` 400kW motor is the largest superconducting machine built in Europe so far, Rockwell has already helped to build a 746kW machine in the US.