A superconducting synchronous generator consists of superconducting field winding, nonmagnetic multi-tubular rotor and airgap armature winding. The superconducting generator has the benefits of 1/2-2/3 weight reduction and 0.5-0.8% efficiency improvement compared with the conventional generator, and the economic crossover between them appears to be 0.5-1.5 GVA. The problems discussed are (1) property, cooling and support of superconducting field winding, (2) thermal contraction of cryogenic torque tube, (3) tubular damper configuration, (4) seal of helium transfer coupling, (5) transposition, cooling and support of airgap armature winding, (6) vibration of the rotor.
The electric field on the outermost shell of superconducting filaments depends directly on the current distribution inside a composite. Calculations are carried out taking into account the axial diffusion due to the resistivity of the matrix. Moreover, the critical state model is modified to account for the dependence of the local current density on the electric field. It is shown that a simple self field measurement is a very good way to evaluate the average transverse resistivity in a multifilament composite. Our samples made of very fine filaments show a resistivity in the range of a few 10-9Ω. m, i.e. much higher resistivity than that of the copper matrix itself. That resistivity decreases as the filament diameter increases. This fact shows that there exists a high resistive barrier at the interface between the superconductor and the copper.
The distribution of the transport current in a twisted multifilamentary composite has been studied experimentally and theoretically by observing the terminal voltage during a sweep of the current for a sample configuration which simulates the windings of superconducting magnets. The theoretical analysis shows that the voltage versus transport current characteristics are directly related to the current distribution inside the composite conductor, and expressions of the voltage are derived for the highly non-uniform current distribution to be expected from the effect of the self-field. The observed voltage agrees well with the theoretical prediction up to a current level of about 60% of the critical current. At higher values an excess resistive voltage develops progressively. The influence of this addistional resistive state on the current distribution and on the self-field instability in discussed briefly.