U-1461
Promising Nanostructural Materials for Cryogenic Electrical Machines
An interest to the superconducting electrical machines that are working at the temperature of 20K caused by two trends of the modern technological progress.
The first is a substitution of traditional carbon-hydrogen fuel by advanced cryogenic ecologically pure fuel for aircraft, on-land vehicles and marine vessels equipped with combustion engines.
The second is a development of the electrical power lines that incorporates transmission of electrical power by superconducting cables having a cryogen (e.g. liquid hydrogen) as a coolant (first of all on the territory of the USA). The superconducting electrical machines for power generating and drive of cryogenic pumps for liquid cryogen transmission are more effective than the traditional ones. They have less weight and higher specific output power and will be of a high demand when transition to cryogenic power technologies starts.
The proposition to use the materials on the basis of magnesium diboride that are synthesised under high pressure-high temperature conditions for the electrical machines has following foundation. The coherence length of magnesium diboride is in the range 1.6-12 nm [1]. Hence, the grain boundaries are not the obstacles for the tunnelling of the coupled charge carriers unlike high temperature superconductors (e.g. YBa2Cu3O7-?). Therefore a production of material of high current density doesn’t deal with long-term growing of a single crystalline-textured structure. The process of bulk magnesium diboride manufacturing is easier and faster than for melt-textured ceramics that is used in superconducting electrical machines. Besides the nano-dimensional defects of structure (e.g., dispersed particles of nonsuperconducting phase or of phase with lower critical current density) can be the pinning centres for magnetic flux lines and, thus, to increase the critical current density [2]. The chemical doping allows creating additional pinning centres and further increasing the critical current density. The use of high pressures can suppress the magnesium evaporation in a synthesis process and allows forming the stoichiometric high dense material with high level of critical current density, the field of irreversibility and trapped field. When working in the superconducting electrical machines the superconducting material is exposed to the high strains. Hence, the high level of mechanical properties of magnesium diboride is very important. The results of investigation carried out in ISM [3-5] showed the possibility to get at high-pressure synthesis the highly dense magnesium diboride based materials with the highest superconducting and mechanical characteristics that are known at present from literature [6-8]. In the frame of this project the deep study of doping effect influence to the structure and properties of magnesium diboride under high-pressure synthesis conditions will be performed. The basis of a technology for the large block synthesis (up to 50 mm in diameter) will be elaborated.
Thus a goal of the project incorporates two problems:
Moscow Aviation Institute (Moscow, Russia) will solve the second problem. Scientific and technological aspects of the development of superconducting electrical machines with MgB2 rotor will be based on the solution of electrodynamic problem of the distribution of magnetic field in the active zone of electrical machine. By that time the properties of active superconducting materials should be known. On the basis of solution of above-mentioned problem main dimensions of electrical machine and its output parameters will be determined. As a basic design the synchronous reluctance electrical machine will be developed. It is expected that machine of immersed design provides an output power up to 1.5 - 2kW at rotating velocity 3000 min-1 and temperature below 20K. Conventional ball bearings of 5 type according to ISO 3290 should provide reliable operating of the machine. Careful testing in cryogenic liquid will assess an accuracy of obtained solutions.
Foreign collaborators will take part in the cross check of obtained results in measuring magnetic and mechanical parameters of the bulk MgB2 elements, produced in ISM, as well as testing of developed electrical machines on the test bench of MAI.
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