As part of the German SupraGenSys project, a fully superconducting generator for wind energy conversion systems was investigated, which will be built and demonstrated as part of SupraGenSys 2. Therefore, this paper summarizes the main challenges and outlines the design strategy to achieve a design with low investment cost and high efficiency. The field winding and the armature winding consist of HTS tapes. The armature winding in particular has high alternating current losses due to the alternating magnetic field. These alternating current losses heat up the coils and must be compensated for by the cryocooler with high energy consumption. A highly efficient generator design can therefore still lead to a low overall efficiency of the system. Or a design with low AC losses can be achieved by using a large amount of HTS tapes, which increases the investment cost of the system significantly. In this paper, design strategies are published to achieve a generator design with low AC losses by identifying the factors that influences of AC losses and developing methods to reduce the losses. For this purpose, the tangential component of the flux density is investigated and the AC losses are determined using the TA formulation [Kim et al. (1962)]. Compared to the methods published in [2], this work focuses more on the overall design of the generator and its stator and rotor windings. The design is iron-based, which allows the use of the iron geometry to influence the AC losses and protect the stator winding from the rotor field. As a result, the AC losses are dominated by the intrinsic field of the coils, which can be influenced by the coil geometry. This enables a design with very low AC losses, high efficiency and modest use of HTS tapes.

For installation in the public electric power grid of the city of Augsburg, Germany, a resistive superconducting fault current limiter (SFCL) was designed, constructed, tested and operated in the framework of a partially funded project ‘ASSiST’. Right from the beginning, it was agreed to aim for a prolonged operation even after closure of the project. This endeavor has been started due to a fundamental need to limit the prospective fault currents at a feeder point of the grid and in order to create long-term operational experience on a device seamlessly integrated into commercial grid components and switchgear, thus demonstrating a high level of readiness for widespread application. It revealed that the SFCL was of robust design – withstanding all electrical tests including a special two-phase fault and sustaining stable cryogenic conditions even during partial outages of the cooling system – and that the technology is reducing loss by shunt reactors. Furthermore, due to the control equipment on medium voltage level, valuable insights on grid behavior could be gained. The extended operation for 4 years has clearly shown the performance and robustness of SFCL technology in feeder points on MV level and provides a reference point for further commercialization.

In an increasing number of electric power grids the share of distributed energy generation is also increasing. The grids have to cope with a considerable change of power flow, which has an impact on the optimum topology of the grids and sub-grids (high-voltage, medium-voltage and low-voltage sub-grids) and the size of quasi-autonomous grid sections. Furthermore the stability of grids is influenced by its size. Thus special benefits of HTS applications in the power grid might become most visible in confined power grids.

High temperature superconducting (HTS) rotating machines show several significant advantages compared to machines built in conventional technique. Former experiments on rotating electric synchronous machines like motors and generators in the power range up to several MW confirmed the well-known benefits of HTS machines like smaller size, less weight and last but not least, a significantly increased efficiency. Especially the increased efficiency of large HTS-Generators up to several hundreds of MW-as operated by utilities-promises an efficient use of fuel and energy sources. This will allow reduced carbon dioxide emissions and becomes more and more important. The development of HTS rotor technology for generators in the range of hundreds of MW bears new challenges. HTS generator windings capable to withstand large centrifugal forces and carrying large currents are required. Also a special cooling system for the rotating winding and further components with novel design will be necessary and have to be developed. In a future HTS generator based on such components, these will have to operate very reliably, so a facility is needed to be able to perform tests. Therefore it is essential to design and build a specific test rig for investigation and test of the required new components. The present paper deals with design and development of such a test rig that allows component tests under realistic conditions, using radii in the range of 0.45 m as in a generator application at rotational speed of up to 3000 rpm, and at low operating temperatures of about 30 K. Additionally a 3 kA high current power supply for HTS test objects like coils or contacts is projected. Aspects of rotor dynamics and fatigue strength analysis had to be considered.

It is specified with a about a rotation axis rotor rotatably mounted a cooling device for cooling an electrical machine, which is disposed on a central rotor shaft. The cooling device comprises at least one disposed on the rotatable rotor shaft thermal coupling element for transporting heat from a radially inner region to a radially outer region. The thermal coupling element dips at least in a partial region of its circumference in a stationary reservoir having a condensed first cooling agents. Furthermore, an electrical machine with a rotatably mounted about a rotation axis rotor, which is disposed on a central rotor shaft, and such a cooling device is provided.

We investigate the use of 2nd-generation High-Temperature Superconductors (2G-HTSs) in the rotors of electrical motors and generators. For these devices the conductor must be wound into robust impregnated coils, which are operated in vacuum at temperatures around 30 K, in strong magnetic fields of about 2T.Differences in thermal contraction between the coil former, conductor constituents, impregnation resin, bandage and heat-sink materials (assembled at room temperature) cause mechanical stresses at operating temperature. Rotating-machine operation adds Lorentz forces and challenging centripetal accelerations up to thousands of g. Second generation-HTS conductors withstand large tensile stresses in axial direction and compression in normal direction. However, shear stresses, axial compression, and tension normal to the conductor can cause degradation in superconducting properties. Such stresses can be mitigated by correct choice of materials, coil lay-out and manufacturingrocess. A certain stress level will remain, which the conductor must withstand. We have manufactured many impregnated round and race-track coils, using different 2G-HTS conductors, and tested them at temperatures from 25 K to 77 K. Degradation of the superconductor in early coils was traced to the mentioned differences in thermal contraction, and was completely avoided in coils produced later. We will discuss appropriate coil-winding techniques to assure robust and reliable superconductor performance. (C) 2012 Elsevier B.V. All rights reserved.

A method for manufacturing a coil (400, 500, 600, 700) with a coil winding (410) comprising the following steps: - arranged providing a strip conductor (300) having a band-shaped substrate web (310) and a tape on the substrate (310) superconductor layer (320), - providing a first winding support, - winding said strip conductor (300) in layers around the first winding support to obtain a coil winding (410) wherein the coil (400, 500, 600, 700) is made such that both at room temperature and at an operating temperature of the coil (400, 500, 600, 700) a positive radial pressure between the layers of the coil winding (410) is made, wherein no strong connection between the strip conductor (300) and the first winding support is produced or wherein a connection between the strip conductor (300) and the first winding support is formed so that it is separated at a voltage of less than 10 MPa, wherein said strip conductor (300) is not bonded to the first winding support, wherein the first winding support made of PTFE formed or coated with a release agent prior to winding the coil winding (410) or sprayed.

A low-speed high-torque HTS machine is being developed at Siemens on the basis of previous steps (400kW demonstrator, 4MVA generator). The goal of the programme is to utilize the characteristic advantages offered by electrical machines with HTS-excited rotor, such as efficiency, compact size, and dynamic performance. To be able to address future markets, requirements from ship classification as well as potential customers have to be met. Electromagnetic design cannot be focused on nominal operation only, but has to deal with failure modes like short circuit too. Utilization of superconductor requires to consider margins taking into account that the windings have to operate reliably not only in "clean" laboratory conditions, but in rough environment with the stator connected to a power converter. Extensive quality control is needed to ensure homogenous performance (current capacity, electrical insulation, dimensions) for the large quantity of HTS (45 km). The next step was to set up and operate a small-scale "industrial" manufacturing process to produce HTS windings in a reproducible way, including tests at operating conditions. A HTS rotor includes many more components compared to a conventional one, so tough geometric tolerances must be met to ensure robust performance of the system. All this gives a challenging task, which will be concluded by cold testing of the rotor in a test facility. Then the rotor will be delivered for assembly to the stator. In following machine tests the performance of the innovative HTS drive system will be demonstrated.

We report on design, construction and testing of a heavy load HTS bearing for a 4 MVA HTS generator. According to the requirement profile of Siemens the bearing was designed for a shaft weight of 1000 kg. To meet these specifications, Nexans has designed and manufactured a HTS bearing fully encapsulated in a stainless steal cryostat with an operation temperature of −240 °C. The working elements of the bearing are single-domain YBCO monoliths fabricated by a top-seeded-melt-growth process, optimized for large batches with 64 pieces per batch. The monoliths exhibit trapped magnetic fields up to 1.4 T and self-field critical current densities at 77 K up to 1.3 × 105 Acm−2. The stator of the bearing comprises 270 such monoliths, which were arranged in nine rings. The levitation properties of the complete system, comprising the HTS stator and a permanent magnet rotor, were recently successfully tested. The system is the largest bearing manufactured worldwide and one of the first to be tested for industrial applications.

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

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