Florian Steinmeyer

380 kW synchronous machine with HTS rotor windings--development at Siemens and first test results

Applying HTS conductors in the rotor of synchronous machines allows the design of future motors or generators that are lighter, more compact and feature an improved coefficient of performance. To address these goals a project collaboration was installed within Siemens, including Automation & Drives, Large Drives as a leading supplier of electrical machines, Corporate Technology as a competence center for superconducting technology, and other partners. The main task of the project was to demonstrate the feasibility of basic concepts. The rotor was built from racetrack coils of Bi-2223 HTS tape conductor, these were assembled on a core and fixed by a bandage of glass-fibre composite. Rotor coil cooling is performed by thermal conduction, one end of the motor shaft is hollow to give access for the cooling system. Two cooling systems were designed and operated successfully: firstly an open circuit using cold gaseous helium from a storage vessel, but also a closed circuit system based on a cryogenerator. To take advantage of the increased rotor induction levels the stator winding was designed as an air gap winding. This was manufactured and fitted in a standard motor housing. After assembling of the whole system in a test facility with a DC machine load experiments have been started to prove the validity of our design, including operation with both cooling systems and driving the stator from the grid as well as by a power inverter.

HTS flux pump for cryogen-free HTS magnets

A reliable method for persistent-current mode operation of HTS magnets is still not available. As an alternative solution to external high-current power supplies we have developed a cryogen-free operating transformer-rectifier type HTS flux pump. Using this device only small ac currents have to be supplied into the cryogenic system. Both thermally triggered HTS thin film switches as well as cryogenic MOSFET switches have been used to operate a conduction-cooled 0.5 T HTS magnet coil. This paper presents results of experimental test and modeling of the flux pump operation.

Field induced transition of the AC susceptibility in high-Tc superconductors

We have investigated the angle and field dependence of the ac susceptibility in Bi2Sr2CaCu2O8 single crystals at low external fields. The ac field was applied perpendicular to the CuO2 planes. The first and third harmonic of the ac susceptibility exhibit a remarkably sharp transition when the dc field component perpendicular to the CuO2 planes crosses a threshold field Hth. Hth is strongly temperature dependent, but is independent of the parallel field component. We prove that these structures are related to the irreversibility line and propose a simple model which excellently explains the measurement data.