Christoph Haberstroh

The BEST PATHS Project on MgB 2 Superconducting Cables for Very High Power Transmission

BEST PATHS (acronym for “BEyond State-of-the-art Technologies for rePowering Ac corridors and multi-Terminal HVDC Systems”) is a collaborative project within the FP7 framework of the European Commission that includes an MgB2-based power transmission line among its five constituent demonstrators. Led by Nexans and bringing together transmission operators, industry and research organizations, this demonstrator aims at validating the novel MgB2 technology for very high power transfer (gigawatt range). The project foresees the development of a monopole cable system operating in helium gas in the range of 5-10 kA/200-320 kV, corresponding to a transmitted power from 1 to 3.2 GW. The main research and demonstration activities that will be pursued over the four-year project duration are: 1) development and manufacturing of MgB2 wires and of the cable conductor; 2) design and manufacturing of the HVDC electrical insulation of the cable; 3) optimization of the required cryogenic system; 4) electromagnetic field analysis; 5) design and construction of a prototype electrical feeding system, including terminations and connectors; 6) testing of the demonstrator; 7) study of grid connection procedures and integration of a superconducting link into a transmission grid; and finally, 8) a socio-economic analysis of the MgB2 power transmission system. CIGRE recommendations will be used to take into account the established international practices, and guidance will be given on newly addressed technical aspects. An overview of the project is presented in this paper, including the main tasks and challenges ahead, as well as the partners and their roles.

Experimental investigation of free convective heat transfer along inclined pipes in high-pressure cryogenic storage tanks

The minimization of heat intake is one of the main challenges in the design process of cryogenic storage tanks. Previous investigations, mostly based on numerical calculations, have shown that connection pipes can increase the heat intake significantly. Under certain geometric conditions a free convective flow field builds up which is able to enhance the heat transfer from the warm end to the cold end of the pipe in a dramatic way. However, this effect is mainly an issue for high-pressure cryogenic storage tanks. In order to investigate the transferred heat experimentally, a test cryostat was designed and manufactured. It is pivot-mounted and can be positioned at any angle of inclination. Inside the cryostat vessel a thermally isolated test pipe with a maximum length of 1 m and a maximum fluid pressure of 200 bar can be placed. This paper gives a closer look at the cryostat design and the measuring principle. First measurement results for a helium filled 20x2x100 mm test pipe under various pressure levels...

Performance measurements of multilayer insulation at variable cold temperature

Multilayer insulation (MLI) is commonly used in most cryogenic devices such as LHe-cryostats or superconductive cables. Typically thermal performance measurements have been carried out using bath cryostats. Inherent to all this devices is a fixed cold temperature at the boiling point of the particular cryogenic liquid. A recent approach for cryogenic pressure vessels covers a broad temperature range, i.e. hydrogen storage from 20 K to ambient temperature. Thus, a new calorimeter cryostat has been designed at TU Dresden to meet these requirements. The design as a flow cryostat allows the measurement of the thermal performance with variable cold temperature between 20 K and 300 K. It can be operated in vertical as well as in horizontal orientation. The insulation material is wrapped around a nearly isothermal cylinder which is held at the desired temperature by a cooling fluid. Preferably LHe respectively helium cold gas is used. Several design features reduce undesired interference errors. It is reported a...

An MgB2 HVDC Superconducting Cable for Power Transmission with a Reduced Carbon Footprint

Superconducting power cables represent a recent innovative development for high-capacity underground transmission. They are set to join the portfolio of technologies that will be needed to accommodate the growing demands on electricity grids. These demands are brought about in particular by the rising amount of renewable energy and the increase in decentralized power generation. The promise of superconducting electric cables lies principally in their small size, with potential advantages in terms of environmental impact, efficiency and public acceptance. The advantages of superconductivity have been acknowledged by the European Commission with its funding of BEST PATHS (an acronym for “BEyond State-of-the-art Technologies for rePowering Ac corridors and multi-Terminal HVDC Systems”), a collaborative project on energy transmission that includes a superconducting power transmission line as one of its five constituent demonstrators. Coordinated by leading cable manufacturer Nexans, the superconducting demonstrator brings together transmission system operators, industry, and research organizations with the aim of validating the MgB2 technology for power transfer higher than 3 GW. In order to investigate the technological maturity of superconducting HVDC links, a monopole cable system based on MgB2 wires and operating in helium gas at 10 kA and 320 kV will be developed and tested in accordance with international practices. In addition to the design, development, optimization, manufacturing and testing activities, special attention will be devoted to studying the integration of a superconducting link into the future transmission grid and to assessing the availability and economic viability of the system. An overview of the project will be presented at the conference, including the main tasks and challenges ahead as well as preliminary results after the first year of activity.

A test rig for analysis of adhesive tapes at 4 K cryogenic temperature

Cryostats and dewar vessels, in particular those used for liquid helium applications, are usually equipped with multi-layer insulation (MLI). Thereby, multiple foils are wrapped around the respective vessels, tubing and components. As standard, different foils are bonded edge to edge using adhesive tapes either based on aluminized non-metallic films or on aluminum foil. There are a number of standard test procedures for adhesive tapes near ambient temperatures (e.g. AFERA 5012/ISO 29863) allowing a standardized characterization of tapes in terms of holding force and long-term reliability. Unfortunately this does not hold true for adhesive tapes to be used at cryogenic temperatures. In this respect, a test rig comprised of a spring-based traction mechanism has been developed by the authors. Combined with a liquid helium dewar, the fabricated test set-up allows a precise and reproducible application of an adjustable tensile load at 4.2 K and measurements of the respective holding time. In the following, the overall set-up including its significant features is described and first experimental results with aluminum tapes are presented.

Neon helium mixtures as a refrigerant for the FCC beam screen cooling: comparison of cycle design options

In the course of the studies for the next generation particle accelerators, in this case the Future Circular Collider for hadron-hadron interaction (FCC-hh), different aspects are being investigated. One of these is the heat load on the beam screen, which results mainly from the synchrotron radiation. In case of the FCC-hh, a heat load of 6 MW is expected. The heat has to be absorbed at 40 to 60 K due to vacuum restrictions. In this range, refrigeration is possible with both helium and neon. Our investigations are focused on a mixed refrigerant of these two components, which combines the advantages of both. Especially promising is the possible substitution of the oil flooded screw compressors by more efficient turbo compressors. This paper investigates different flow schemes and mixture compositions with respect to complexity and efficiency. Furthermore, thermodynamic aspects, e.g. whether to use cold or warm secondary cycle compressors are discussed. Additionally, parameters of the main compressor are established.

Simulation of MLI concerning the influence of an additional heat load on intermediate layers

Multilayer insulation (MLI) is commonly used in most cryogenic devices such as LHe cryostats or storage vessels. Numerical and experimental studies of such insulation systems are known from literature. The temperature distribution of intermediate layers has been investigated as well. Experiments using temperature sensors, for example thermocouples, to determine the temperature of intermediate layers had been described. Naturally such wiring causes additional heat load on the respective layer and influences the equilibrium temperature. A mathematical model of heat transfer through MLI has been developed to investigate the temperature distribution across the MLI layers. The model comprises a combination of radiation, residual gas conduction and conductive heat flux. An analysis for variable cold and warm boundary temperatures and various residual gases and pressures is carried out. In addition to the model an experimental test rig will be built for the verification of the model. The paper presents the influence of an additional heat load on an intermediate layer on the temperature distribution and on the overall thermal performance of MLI.