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World`s largest superconducting motor starts to spin
Published:  01 August, 2000

World`s largest superconducting motor starts to spin

A 1,000 horsepower (746kW) superconducting motor, claimed to be the largest built to date, has passed its initial tests in the US. The motor (shown below) has been built jointly by the American Superconductor Corporation (ASC) and Rockwell Automation, and is part of a $21m Government-backed programme aimed at commercialising motors based on high-temperature superconductors (HTSs).

The potential advantages of the HTS motors compared to conventional copper-wound machines include higher efficiencies, smaller sizes and lower manufacturing costs, especially for large machines.

The HTS wires used instead of the copper windings can carry currents 100 times larger, thus producing much stronger magnetic fields in a given volume. The result is that an HTS motor can be a fifth of the weight and size of a similarly rated standard motor. This, in turn, means that it should be possible to make the motors on continuous assembly lines and to ship them directly to customers without the costly disassembly and on-site re-assembly needed for large standard motors.

In addition, HTS machines can eliminate the iron used in conventional motors, lowering the armature inertia and reducing the frictional load on the motor bearings. The removal of iron teeth from the armature also allows more room for armature copper, cutting losses and boosting efficiency further.

There are other claimed benefits, including lower noise levels and smoother operation. And because the HTS motors operate at small load angles - 15 degrees rather than 70 degrees for a conventional motor - they have much higher peak torque capabilities (around 300%) and can withstand large transients without losing synchronous speed.

The prototype 1,000hp motor is located at Rockwell`s Cleveland research centre. Joseph Swann, president of the company`s power systems division, is hailing the successful demonstration of the motor as "a significant engineering achievement". Testing on the 1,000hp will continue at least until at the end of this year when the motor may be transferred to an industrial installation.

The motor is part of a $21m HTS research and development programme, half of whose costs are being met by the US Department of Energy (DOE). The next phase will be the development of 5,000hp (3.73MW) motor, due to start testing next spring. This will be a critical stage because, at 5,000hp, HTS motors will start to compete directly on price with conventional machines. The diagram below shows how much smaller a 5,000hp HTS motor (right) will be than existing machines (left).

In parallel with this work, American Superconductor is independently developing another 5,000hp HTS machine optimised for low cost rather than efficiency. ASC`s president Greg Yurek explains that this project began about two years ago when it became clear that many potential customers were more interested in low purchase costs than in energy efficiency or lifetime costs.

The ASC engineers therefore started work on designing a new HTS motor that would be up to 40% cheaper to manufacture than a conventional large motor. This work has resulted in an ultra-compact design which, with an efficiency of 97.5%, will still be about 0.5% more efficient than a standard motor even though it is not as efficient the 98.5% of the 5,000hp machine in the DOE programme. ASC has applied for patents on its design.

The first ultra-compact HTS machine will be ready for testing at about the same times as the DOE machine, next spring. Greg Yurek envisages a two-year field trial programme involving about 10-15 motors. He expects them to go on sale in three to four years, starting with 5,000hp models but then expanding to both bigger and smaller machines.

Yurek predicts that when the motors do reach the commercial stage, "they will really disrupt the business". At present, the $1bn market for motors above 1,000hp is characterised by cut-throat competition and low profits. Yurek believes that the smaller, lower-cost HTS machines will revolutionise the market and open up new applications. He says his company is talking to potential motor manufacturing partners in Europe and Japan as well as in the US.

In addition to its work on the 5,000hp motors, ASC is also designing a 33,000hp (24.6MW) HTS machine for the US Navy. This motor, intended for ship propulsion, will be cheaper, smaller, lighter, more efficient and quieter than conventional marine motors.

Another promising market is for HTS generators, which will use a similar technology to the HTS motors. The market for generators larger than 30MW is estimated to be worth around $2bn.

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