A conduction cooled superconducting dynamo recently built at Robinson Research Institute provides 200 A current to energise the field coils of a 10 kW high speed superconducting motor. Unlike previously built superconducting dynamos, this example is engineered so the peak efficiency current range of the HTS dynamo matches the nominal operating current of the ReBCO motor field coils. In addition, this HTS dynamo is designed to operate inside a vacuum, without an iron yoke, and with a non-cryogenic rotor, reducing the overall cryogenic cooling load and improving coil energisation efficiency.

HTS dynamos are type of superconducting flux pump that enable wireless DC energisation of fully superconducting circuits. These devices utilise the non-linear E-J behaviour of a type-II superconductor to rectify the shielding current induced by permanent rotor magnets passing over a superconducting stator tape. This results in DC voltage along the tape length. Because the magnets and superconducting tape must rotate relative to each other, HTS dynamos are well suited to superconducting motor applications where efficient and reliable energisation of rotating field coils is required.

Conventional superconducting motor field coil energisation requires a current supply matched to the field coil operating current, and non-superconducting circuit components including sliding brushes and current leads that penetrate the cryogenic rotor envelope. Wireless energisation via HTS dynamo replaces each of these components with a lightweight and more cryogenically efficient alternative. Multi-kiloamp currents are induced in the fully superconducting field coil circuit from a low current source, removing the need for a high current DC supply. Non-superconducting cryogenic envelope penetrations are removed as the HTS dynamo transmits power wirelessly. As these are typically highly thermally conductive copper leads, their removal reduces the cryogenic cooling power required to maintain field coil operating temperature. Wireless power transmission also removes the need for sliding contacts between the field coils and their power source.

Previous work on HTS dynamos revealed yoke iron and liquid nitrogen drag to be large contributors to overall system losses. The newly developed HTS dynamo built at Robinson Research Institute has a yokeless design, and is conduction cooled in a vacuum to remove liquid nitrogen drag.

This presentation will introduce the HTS dynamo and its operating principle, illustrate the development process used to match the HTS dynamo output to the AC Homopolar motor field coil requirements, and describe the challenges of designing this conduction cooled device which has cryogenic and room temperature components in close proximity.

Keywords: Flux Pump, Coil Energisation, Current Supply, Brushless Exciter