New superconducting transformer is light and compact

Researchers from the Technology Foundation STW and the University of Twente, in cooperation with Smit Transformatoren and Smit Draad, have developed a prototype coil for a superconducting transformer which is not only light and compact but also energy-efficient. A keen interest has already been expressed by several companies.

The coil is made from superconducting wires, insulated using a newly patented method. Furthermore, together with Smit Transformatoren the researchers have developed a method to wind coils from the fragile conductor.

The superconducting wires are manufactured from a ceramic material BSCCO (pronounced `bisko`). This so-called high-temperature superconductor only allows current to flow without resistance when the material is cooled to -196 degrees celcius. The new insulation had to be able to withstand such low temperatures. Therefore the researchers chose a polyimide-film.

A silver casing covers the thin filaments of the superconducting material to prevent them from breaking. Like the tape in an audio cassette, the superconductor is rectangular in cross-section, 4 mm wide and 0.3 mm thick. A conventional insulating technique with a coating would make the rectangular conductors unreliable because the coating on the sharp edges of the conductor would be too thin. As a result of this sparks could easily jump (discharge) and damage would be caused.

In order to prevent damage, the STW researchers developed an alternative insulating procedure. Together with Smit Draad they developed a method in which an insulating layer is folded lengthways around the superconducting tape. The insulation prevents discharges up to several kilovolts.

The method has already been implemented at the request of various companies. For example, the market leader ASC (American Superconductor Corporation) sells conductors which have been insulated by Smit Draad.

The research group anticipates various applications for compact and light superconducting devices in which the new superconducting coils and cables will play a role. The compact construction of the transformers makes their use in trains attractive. Also the superconducting cables could guarantee the energy supply to large users such as the computer industry or compact town centres. The high resistance of the current copper cables means that too much warmth is released during the transport of electricity.

The STW has signed a contract with Smit Draad for the use of knowledge obtained from the STW project.