Naotake Natori

AC Loss Characteristics of Superconducting Power Transmission Cable

Characteristics of lOm-long Nb3Sn superconducting power transmission cables are described. Cables are designed to be suitable for power of 1 to 3 GW and are assembled using Nb3Sn superconducting tapes.

Conductor pitch effect on an eddy current loss of the superconducting power cable using the disassembled cable "N" data

The origin of the difference between measured AC loss and that of the short sample test has been studied. The axial field due to disordered pitch of conductor and shield tapes has a trivial effect on the eddy current loss in the stabilizer. The displacement of the current direction on the conductor from its lay angle makes comparable eddy current loss.

Measured-loss analysis of superconducting power transmission cable

In the former work (see T.Hoshino et al., ibid., vol.9, no.2, pp.1277-80, 1999), the eddy current loss in the former due to pitch difference between current conductor and shield conductor was studied. The calculated value was negligible small which does not explain the measured value. The eddy current loss due to radial component of the magnetic field become comparable with the measured value. In this paper, the reason of the increased loss is revealed. The disturbance of the conductor pitch yields different strength of the axial magnetic field. The difference of the axial flux toward the radial direction as the radial component of the flux. The flux causes eddy current loss in the copper for stabilizer. It is well match with the measured value.

How to recognize superconducting rotor sound by AE

New evaluating methods for rotating superconducting magnets have been developed by observing acoustic emission (AE) from the rotating machine. First, by measuring the AE level, we can learn whether the conductor is changing from a super to a normal state or not. Secondly, we can get to the area of the magnet the normal state was propagated in by comparing the AE signals level of each channel. Thirdly, we can estimate how large a quenched magnetic energy to dissipated in the magnet by measuring the recovery of time constant of the AE signals. Fourthly, we can detect the difference between the AE just before and after the jumps of heat flux by analysing the AE spectrum. Finally, we report how we can predict from what areas the incoming natural quench of the magnet will be initiated, by monitoring the AE level of each channel.

A study on stability of rotating magnets

Stabilities of magnets in a high gravitational field up to 2000 G are discussed, based upon the experimental results of forced quench tests in a set of rotating magnets, in order to establish the stability design criterion of field windings of superconducting generators. Relations of propagation velocities, recovery currents, minimum quench energy and heat transfer characteristics are studied, a good agreement between the experimental results and a theory confirmed the improvement of magnet stability in a high gravitational field because of the enhanced heat transfer characteristics.