Heinz-Werner Neumüller

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.

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.

Advances in the development of synchronous machines with high-temperature superconducting field winding at Siemens AG

Synchronous machines employing high-temperature superconductors offer several significant advantages compared to conventional ones. The development of superconducting electrical machines has a long tradition within Siemens AG. Starting with low-temperature superconducting materials in the 1970s, more than 30 years of experience in the field of superconducting electrical machinery have been accumulated. This knowledge represents the foundation for current research and development activities, which lead to the successful completion of a 4 MVA synchronous generator with a high-temperature superconducting field winding for ship-borne application. At this time, this generator represents the worlds highest rated 2-pole, 60 Hz HTS-machine. This paper reflects on recent development programs carried out successfully, including selected test results of the 4 MVA HTS-machine, and gives an insight into current development activities in the field of high-temperature superconducting electrical machines at Siemens

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.

Low-pressure large-area magnetron sputter deposition of YBa2Cu3O7?? films for industrial applications

This paper addresses the development of a technically relevant sputter-deposition process for YBa2Cu3O7−δ films. First, the simulation of the particle transport from target to substrate indicates that only at a reduced pressure of p ≈ 1–10 Pa can a sufficiently large deposition rate and homogeneous stoichiometric distribution of the particles during large-area deposition be expected. The results of the simulations are generally confirmed by deposition experiments on CeO2 buffered sapphire and LaAlO3 substrates using a magnetron sputtering system suitable for large-area deposition. However, it is shown that in addition to the effect of scattering during particle transport, the conditions at the substrate lead to a selective growth of Y–Ba–Cu–O phases that, among others, strongly affect the growth rate. For example, the growth rate is more than three times larger for optimized parameters compared to the same set of parameters but at 100 K lower substrate temperature. Stoichiometrical and structural perfect films can be grown at low pressure (p < 10 Pa). However, the superconducting transition temperature of these films is reduced. The Tc reduction seems to be correlated with the c-axis length of YBa2Cu3O7−δ. Two possible explanations for the increased c-axis length and the correlated reduced transition temperature are discussed, i.e. reduced oxygen content and strong cation site disorder due to the heavy particle bombardment.

Current Capacity of Ag/Bi-2223 Wires for Rotating Electric Machinery

With focus on the application in rotating electric machines we measured the dependence of current capacity of Ag/Bi-2223 wires on temperature and magnetic field. Even for wires stemming from a single manufacturer we observe a significant spread of wire properties. We study different temperature and magnetic field dependence by a parallel path model which allows for a quantitative analysis. The implications of experiments and modelling are discussed with regard to the further wire development and for application within windings.

Numerical calculations of a hybrid power train for motor vehicles

In a cooperation between the dutch TNO and Siemens AG a hybrid power train for motor vehicles is analysed, constructed and put on a test bed. The power split solution comprises two coupled concentric electrical machines, for which various numerical calculations are performed.