Joachim Frauenhofer

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.

Design Challenges and Benefits of HTS Synchronous Machines

HTS (high temperature superconducting) rotating machines are about to cross the barrier from the laboratory stage to marketable products. Several demonstrators, prototypes were developed and even first commercial products do already exist. In order to benefit from excellent features of HTS machines like e.g. superior efficiency, low mass and volume as well as substantially improved dynamic characteristics several design challenges have to be encountered. These challenges differ in several ways from those experienced with conventional machines. The paper provides a general overview on HTS machine topologies under development today and reflects on different areas of applications. Design challenges typical for HTS machines are discussed and differences as well as similarities compared to conventional machines are identified. Examples based on recent development projects at Siemens AG are presented. The paper should help to make typical design considerations and resulting requirements for HTS synchronous machines more transparent for the users of industrial applications.

High-Temperature Superconducting Rotating Machines for Ship Applications

Main applications for rotating electric synchronous machines are given as generators and motors; a small niche can also be found in synchronous condenser-applications. High temperature superconducting (HTS) rotating machines show several significant advantages over machines built in conventional techniques. These are mainly increased efficiency, higher power density, and enhanced electrical stability. Especially for on-board applications, these properties may be decisive to save fuel and space and improve the capabilities. In the past, basic programs were carried out to demonstrate in principle the possibility to build such machines. Meanwhile these programs have shown great success and the feasibility of HTS machines for such applications has come into reach. For that reason developments for HTS machines in the megawatt-range are now being in progress, for propulsion purposes as well as for power generation applications. Started with the built of a 400 kW model motor that has operated successfully for more than two years, Siemens is now being engaged in the development of HTS machines for all electric ship application in the megawatt-range. A demonstrator for a 3600 rpm 4 MVA generator has been set up in the Nuremberg test facility for extended type and system testing. Results of tests with both machines will be presented. Technical implications of this new technology for ship-borne application will be discussed together with general economic assessments

Advances in and prospects for development of high-temperature superconductor rotating machines at Siemens

We report on the successful manufacture and testing of the Siemens 400 kVA HTS synchronous motor, which has been in operation for over 3 years, and on the progress of the 4 MVA synchronous motor/generator, which has been manufactured and is now in a phase of extended testing. Furthermore, the benefits of HTS machines will be discussed with emphasis on applications in ships. The development of future marketable products will be strongly dependent on the progress of secondary technologies, such as wire performance and efficient cost-effective refrigerators.

Operational Experience With the World's First 3600 rpm 4 MVA Generator at Siemens

HTS-excited synchronous machines provide substantial advantages with respect to efficiency, size, and operational behavior, with special focus on ship or off-shore applications. A 400 kW machine had been designed and built as technology demonstrator at Siemens to explore the feasibility of critical components and system interactions. After successful conclusion of these tests a first real-size machine was addressed: a 4 MVA HTS generator as core of a ship power generation system. This generator has been designed and manufactured and was subjected to extended testing in the Siemens A&D Large Drives systems test facility at Nuremburg, Germany. No problems were encountered caused by the high local centrifugal acceleration acting on rotor components, like e.g. the HTS windings. The cooling system was designed to provide power for cooldown, but also reliability and redundancy in operation, and performed as expected. The 6.6 kV air-cooled armature is an air-core winding made from Litz wire. The resulting machine characteristics were determined, the efficiency including rotor cooling system was measured and found to be about 2% superior to conventional generators of same power. Additional tests are going on, coupling the machine to a power converter and operating as a variable speed drive. In order to understand the frequency-dependant interactions detailed FE simulations were performed. This know-how aims to design an HTS machine as efficient inverter-driven motor, as one of the promising applications of synchronous HTS machines are high-torque propulsion motors for all-electric ships.

Thermosyphon Cooling System for the Siemens 400kW HTS Synchronous Machine

A commercial GM cryocooler is employed to cool the rotor of the first Siemens 400 kW HTS machine. Excellent thermal connection between cold head and rotor is achieved using a thermosyphon. At the rotor’s inner surface the required cooling power is provided by evaporating fluid, that is recondensed at the coldhead. Our configuration allows an easy mechanical decoupling of the stationary cold head and the rotor, using a magnetic liquid rotary seal. In order to shorten cool‐down time, a precool to 70 K is done with a thermosyphon filling of nitrogen, while a motor operating temperature of 25 K is reached using neon. Temperature difference between the thermosyphon’s cold and warm ends is below 1 K for a heat transfer of 40 W. During operation, a temperature controller stabilizes condenser temperature and hence rotor temperature. The self‐regulating cooling system has been operated continuously and without problems since Spring 2001. The machine was also operated with newly developed pulse‐tube cryocoolers, th...

High-temperature-superconducting machines- a high-technology step for large rotating electric machines

The presently available high temperature superconducting materials (HTS) transport electric current at high current densities with negligible electric losses. This makes it possible to create higher magnetic fields. Using these features in a rotating electric machine it is possible to reduce the over-all dimensions and weight of the machine, to increase the efficiency and to improve additional features of the machine. To address these goals Siemens started three R&D projects to develop, manufacture and test electric machines with high temperature superconducting field windings. A 400 RW synchronous motor was followed up by a 4000 kVA high speed generator. A 4000 kW high-torque motor will be the third step. Additional to the application in electric machines it is possible to use the substantial advantages of high temperature superconducting materials for passive magnetic bearings. These are operating without any control device of the magnetic field. Siemens started the development of heavy load HTS bearings in parallel to the development of HTS machines

Advances and prospects of HTS rotating machine development at Siemens

Siemens has a long tradition in developing superconducting technology, from the early 60s starting with Helium-cooled LTS magnets till today covering a wide range of potential applications. High temperature superconductors (HTS) can operate at much higher temperature (25-77 K), which has initiated world-wide activities for industrial applications to power engineering. At present superconducting rotating machines are in the focus enabling a wide spectrum of power varying from industrial drives of some MW to several hundreds of MVA for large generators and speed ranging from the slow motion of wind power generators or of high-torque ship drives to high-speed generators coupled to gas turbines. This paper reports about the successful manufacturing and testing of the Siemens 400 kVA HTS motor, which has been in operation since 2.5 years. In the meantime a 4 MVA motor/generator is under manufacturing and technoeconomic studies have also shown interesting economical perspectives for large power plant generators

Numerical calculations for high-temperature superconducting electrical machines

To achieve a reliable design of a high-temperature superconducting (HTS) electrical machine, a multi-level approach including analytical and numerical techniques is state of the art. In this paper some light is shed on computational electromagnetics simulations performed at Siemens AG during the design procedure of a HTS synchronous machine.