A high temperature superconductor (*1) motor-applied pod propulsion system has been completed for practical-level verification tests

A Japanese frontier group (**A) has developed a AC synchronous high temperature superconductor motor (HTS motor) using bismuth-based high temperature superconductor wire(*1) cooled by liquid nitrogen (LNx) and a pod type marine propulsion system(*2) incorporating the HTS motor has been completed. This is the world’s first attainment that the superconductor motor has gotten closer to the practical use. The group is formed by industrial companies and a university including Ishikawajima-Harima Heavy Industries Co., Ltd. (IHI) that acts as a leader of the group.

The group is now conducting tests on the pod propulsion system to estimate the underwater performance in the water tank for hydraulics belonging to the IHI Technical Operation, which is sited at the IHI Yokohama Works. The pod type propulsion system is 0.8m wide and 2m long and has a 1m-diameter propeller. Under the tests, the propeller rotation was confirmed to be freely controllable for both clockwise and counterclockwise directions within the propeller speed range from 0 to 100rpm(*3). This encourages the group to develop a commercial type. (Based on our knowledge, the pod type propulsion system using a LNx cooling synchronous superconductor motor is the world’s first product.)

Good test results as designed, which are indicated below, have so far been obtained from the tests, showing that very little noise and magnetic flux from the motor. It is thus confirmed that the HTS motor is versatile in use. The group has a plan to place a commercial HTS motor of 500kW and 220rpm in the market, preparing a setup for order receiving activities.

The newly-developed HTS motor production is possible using mass-producible high-temperature superconductor wire material and LNx as a coolant for the wire. LNx had previously been difficult to use as a coolant for such superconductor motor. The patent technologies owned by the group members have cleared away the difficulties involved in the commercialization of the super conductor motor.

The electric current applied to high-temperature superconductor wire is greatly influenced by magnetic flux and temperature interlinking with the high-temperature superconductor wire. When using LNx as a coolant, the conventional technology could not generate high-density magnetic flux of the field system for a large-capacity motor. The group has overcome this technological difficulty with the Flux Collector (FLC : the registered trademark applied to the patent office) that has been developed to intensify the magnetic flux density, in which the magnetic flux interlinked with the superconductor wire has been made small.

The FLC has a highly magnetism-transmittable material in the core of the field-system, which permits intensive transmission of the magnetic flux. This has enabled the large electric current flow under the temperature of LNx, and as a result, a very intensified density of the magnetic flux cloud be obtained. Thereby, the size of the HTS motor has reduced to one tenth of the conventional synchronous motor while allowing a large output.

The pod type propulsion system has been selected first to apply the HTS motor to demonstrate characteristics (**B) of the motor best. This propulsion unit is outfitted the outboard of a ship. Therefore effective utilization of the inboard space of the ship increases; noise decreases; and maneuverability of the ship becomes better (the ship turning is possible in a short range -- about a half of that of the conventional propulsion system). Due to these merits, the pod type propulsion system has become popular for the ships such as passenger/car ferries in Europe and the US. However the pod-type propulsion system incorporating the conventional motor or permanent-magnet motor becomes a greater and impractical size in the outer diameter when making its output larger. Inevitably, the pod-type propulsion system of the smaller size but larger output had been demanded so far.

The HTS motor is a new epoch in developing the small size for the pod-type propulsion system, which will decrease the outer diameter to the half of that of the conventional unit. Propulsion efficiency will increase by 3 to 5% in addition to the improved efficiency of the motor itself. Moreover, the HTS motor is friendly to the environment.

With these features, the HTS motor will thus be used for various purposes (**C). Furthermore, preceding Europe, the US, and Korea, the frontier group will complete the prototype for the practical use of the fully high temperature superconductor motor (FHTS motor) (*4) in March this year.

Note:  (**A ) (Alphabetical order) University of Fukui (Professor Hidehiko Sugimoto); Fuji Electric Systems Co., Ltd.; Hitachi, Ltd.; Ishikawajima-Harima Heavy Industries Co., Ltd.; Nakashima Propeller Co., Ltd.; Niigata Power Systems Co., Ltd.; Sumitomo Electric Industries Co., Ltd.; and Taiyo Nippon Sanso Corporation.


(**B ) Features of the HTS motor
1. "The cheap and easily-handled LNx coolant," which was difficult to use in the past, is usable.

2. It is smaller and lighter than the conventional motor (1/10 in volume and 1/5 in weight in case of the 5000 kW motor).

3. Mass-produced superconductor wire is used, which can be produced by the kilo meter unit.

4. There is less generation of noise of the motor and leakage of magnetic flux from the motor.

5. The outer surface of the SS motor is the normal temperature although the inside is the cryogenic temperature. So the HTS motor is used at any service place.

6. It is possible to power up by adding coil units (available by 500kW unit). Even if one of coils is broken down, the remainder will maintain running.

(**C ) Main use of the HTS motor
1. The motor is suitable for the marine electric propulsion equipment (Particularly for the pod type propulsion system).

2. The motors for the railroad

3. The generator can be used for the wind power generation equipment (the synchronous motor is convertible to a generator when the rotor rotates by the outside power).

4. The motor is usable for other large power requirement (drives for the steel rolling mills, the blower of large capacity, etc.)


*1  High-temperature superconductivity : This means that the electric resistance of a conductive material becomes zero around minus 200oC or higher.

High-temperature superconductor bismuth-based electrical wire: An electrical wire made of high-temperature superconductor material that can conduct electric current more than 100 times of the conventional material.

*2  The pod type propulsion system: An outboard propulsion unit attached to the outside of the ship bottom. The propulsion drive unit is contained in a pod.

*3  The design values are 12.5kW for the rated output (62.5kW for short time) and 100rpm for the motor speed at the liquid-nitrogen temperature of 66K. This HTS motor has the same torque as that of a 937kW and 1,500rpm motor.

*4  Fully high temperature superconductor motor: Based on the prototype HTS motor, the FHTS motor will be developed using a superconductor armature (the armature of this HTS motor is not superconductor) besides the field system, which has already employed for the HTS motor. Thus electric wire used for the whole of the field system and the armature will be the superconductor electric wire, making heat generation from the motor almost zero. Eventually, this will allow not only but reducing the size of motor but also eliminating the external motor-cooling installations that include ancillary equipment for water and air cooling. The effective space in board the ship will be widened. The increase in superconductor wire to make the HTS motor fully superconductor will not require any additional superconductor cooling facilities except the LNx cooling equipment originally provided because the heat generation from the superconductor electric wire will become nil.



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