Sumitomo Electric Develops Liquid Nitrogen Cooled Superconducting Motor for EVs

12 June 2008

The prototype motor. Click to enlarge.

Sumitomo Electric Industries Ltd. (SEI) unveiled an electric vehicle equipped with a prototype superconducting motor cooled by liquid nitrogen and built using SEI’s high-temperature superconducting (HTS) wires.

High-temperature superconducting wires, cooled to about -200° C, can reduce electrical resistance to almost zero. The EV can run about 13% longer than an electric vehicle using a conventional copper wire motor, the company said.

In September, 2007, a Japanese research group coordinated by IHI Corporation and including SEI unveiled a 365 kW HTS motor cooled by liquid nitrogen and using SEI’s DI-BSCCO superconducting wire. SEI’s bismuth-based superconducting material is made of bismuth - strontium - calcium - copper - oxygen (Bi-Sr-Ca-Cu-O).

Cutaway of the 365 kW HTS motor announced in September 2007. Click to enlarge.

In 2005, the Japanese research group developed a flux collector based on the idea of applying a large current to the coil while reducing the magnetic flux, and completed the world’s first practical-level liquid-nitrogen cooled HTS motor using this flux collector and SEI’s DI-BSCCO superconducting wire. The group then worked to improve motor capacity and developed the practically applicable 365 kW HTS motor.

The 365 kW HTS motor has the following three main features:

• In other HTS motors, only the field coil (DC coil) have HTS wires wound around it. However, the research team applied a low AC-loss design to the armature windings (AC coil) by adopting a flux collector.

• When HTS coils were set in a parallel configuration, non-uniform current distributions occur in the coils. In order to solve this problem, the operating current for each coil was precisely controlled.

• Earlier HTS motors were required to have a mechanism that allows coolant to circulate through the shaft. However, the HTS motor designed by the Japanese frontier research group has the fixed superconducting armature windings and is without the cooling system using a shaft. This new design enables two motors to be connected in tandem using both ends of the shaft and thus improve the motor’s capacity.

The group is constructing a superconducting propulsion unit for directly driving a contra-rotating propeller by connecting the newly developed 365 kW HTS motor in tandem with a 50 kW HTS motor developed in 2006.

SEI expects larger powered applications of this HTS system to be developed, up to 2,500 kW, for marine applications.

The group included, in alphabetical order: Fuji Electric Systems Co., Ltd.; Hitachi, Ltd.; IHI Corporation; Nakashima Propeller Co., Ltd.; Niigata Power Systems Co., Ltd.; Sumitomo Electric Industries, Ltd.; Taiyo Nippon Sanso Corporation; and University of Fukui (Prof. Hidehiko Sugimoto).

The EV with prototype HTS motor. Click to enlarge.

Sumitomo is also downsizing the applications of the HTS motor system for application in light duty vehicles. The company said that it will continue to work to improve the performance of the prototype EV motor, which is targeted for application in light-duty passenger vehicles. Applications of superconducting motors for buses and large trucks are also underway. The company sees the motor as being practical within 10 years.