Peter Kummeth

Resistive current limiters with YBCO films

The aim of this work is to develop a function model of a resistive HTSC fault current limiter. The switching elements of the fault current limiter are bath-cooled in a liquid nitrogen cryostat. The elements consist of YBaCuO films which are deposited on different substrates with critical current densities of up to 3/spl middot/10/sup 6/ A/cm/sup 2/. For the most effective limiting samples so far the peak let-through current was twice tile nominal current and the steady short-circuit current below nominal current. The concept of a 100 kVA function model is introduced.

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

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

Development and test of a 100 kVA superconducting transformer operated at 77 K

High-temperature superconducting (HTS) transformers are very promising candidates for application in electrical power engineering. Their main advantages are reduced size, weight, better efficiency and reduced potential fire and environmental hazards. We have designed, constructed and tested a 100 kVA HTS power transformer operated at 77 K. The nominal primary and secondary currents (voltages) are 18 A (5.6 kV) and 92 A (1.1 kV), respectively. No-load tests, short-circuit tests and load tests proved repeatedly that the transformer has the rated capacity. HTS winding losses of 20.6 W and iron losses of 403 W were measured.

Development of superconducting magnetic bearings

Abstract The interaction between high temperature superconductors (HTS) and permanent magnets allows to realize an inherently stable contactless bearing without active feedback system. It has no wear, very low friction and allows operation at high rotational speed. Its thermal inertia prevents a sudden breakdown. High magnetic gradient bearings with a special magnet configuration work both radially and axially. We have designed and constructed a test set-up with two HTS journal type bearings. Investigation of characteristic bearing features was performed in quasi-static experiments with different YBCO stators. Stiffness of the bearings and the dependence of losses per force–displacement cycle on the amplitude were characterized. Losses per force–displacement cycle were investigated in dynamic measurements with frequencies between 0.01 and 40 Hz and resulted in nearly frequency independent behaviour.

Design and Development of a Test Rig for HTS Generator Components

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.

Aspects on HTS applications in confined power grids

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.