Superconducting coils for contactless power transmission

2 min read

A team pf scientists, led by Technical University of Munich (TUM) physicists Christoph Utschick and Prof. Rudolf Gross, has succeeded in making a coil with superconducting wires capable of transmitting power in the order of more than five kilowatts contactless and with only small losses

The team involved in the project said that a wide range of conceivable applications included autonomous industrial robots, medical equipment, vehicles and even aircraft.

Contactless power transmission has established itself as a key technology when it comes to charging small devices such as mobile telephones and electric toothbrushes, but there is also growing interest in contactless charging for larger electric machines.

These types of devices could be placed on a charging station whenever they are not in use, so making it possible to effectively utilize even short idle times to recharge their batteries. However, current transmission systems for high performance recharging in the kilowatt range and above are large and heavy, since they are based on copper coils.

Working in a research partnership with the companies W├╝rth Elektronik and superconductor coating specialist Theva D├╝nnschichttechnik, a team of physicists at TUM have succeeded in creating a coil with superconducting wires capable of contactless power transmission in the order of more than five kilowatts (kW) and without significant loss.

Minor alternating current losses can occur in superconducting transmission coils and these losses grow as transmission performance increases - the surface temperature of the superconducting wires rises and the superconduction collapses.

To address this problem the researchers developed a special coil design in which the individual windings of the coil are separated from one another by spacers.

"This trick significantly reduces alternating current loss in the coil," said Christoph Utschick. "As a result, power transmission as high as the kilowatt range is possible."

The team chose a coil diameter for their prototype that resulted in a higher power density than is possible in commercially available systems.

"The basic idea with superconducting coils is to achieve the lowest possible alternating current resistance within the smallest possible winding space and thus to compensate for the reduced geometric coupling," explained Utschick.

However, making the distance between the windings of the superconducting coil too small can result in superconduction collapse during operation. Larger separations would on the other hand result in lower power density.

"We optimised the distance between the individual windings using analytical and numerical simulations," said Utschick. "The separation is approximately equal to half the width of the tape conductor."

While the researchers now want to work on further increasing the amount of transmittable power, they still have to overcome the problem that the coils used require constant cooling with liquid nitrogen, and the cooling vessels cannot be made of metal.

"This will mean an extensive amount of further development effort," conceded Rudolf Gross, Professor for Technical Physics at the Technical University of Munich and Director of the Walther-Meissner-Institute of the Bavarian Academy of Sciences and Humanities. "But the achievements up to now represent major progress for contactless power transmission at high power levels."