Yue-Jin Tang

Quench current-time characteristics of four kinds of superconducting cable

Abstract A superconducting cable changes from the superconducting to the normal-conducting state at different current levels due to a.c. overcurrents with different magnitudes. We have defined this feature as the quench current-time characteristic, i.e. the I q − t characteristic. In this paper, the I q − t characteristics of four kinds of superconducting cable are experimentally discussed. The results proved that the I q − t characteristics of these four superconducting cables are different from each other and that these differences are induced by the quench developing process among the strands of the superconducting cables.

Position of quench initiation in 6 kV-200 A class superconducting fault current limiter

The authors have developed a 6 kV-200 A class superconducting fault current limiter (SC-FCL). The SC-FCL has eight co-axial coils connected in order to minimize total inductance. In the present paper, taking consideration of the self-magnetic field in the SC-FCL, they discussed the position of quench initiation. They calculated spatial profiles of the strength and the direction of the self-magnetic field in the SC-FCL. As a result, the self-magnetic field is applied to sections of the superconducting cable (SC cable) in the transverse direction (maximum value: 6.42/spl times/10/sup -4/ T/A). The connective section between coils, however, suffers a magnetic field with a longitudinal component of 3.34/spl times/10/sup -4/ T/A. In the case of a short sample of the SC cable which was used for the SC-FCL, the quench current levels were found to decrease at the rate of 40 A per 0.1 T in a transverse magnetic field and 100 A per 0.1 T in a longitudinal field. Taking these results into consideration, the authors pointed out that the quench may be initiated in the connective section between coils, where the self-magnetic field is applied in the longitudinal direction.

Current limiting level-time characteristic of a superconducting fault current limiter

Abstract A model superconducting fault current limiter (SE-FCL) has been developed. The adopted superconducting cable is composed of six strands insulated from each other. The current limiting level of the SC-FCL is measured under two types of overcurrent, a sinusoidal and an inrush current. The results show that the current limiting level of the SC-FCL I q increases with an increase in the rate of rise of the overcurrent. By introducing a new parameter of time-to-quench t f , it is found that I q increases with decreasing t f . This feature is taken as a current limiting level-time characteristic i.e. the I q - t f characteristic. The existence of the I q - t f characteristic found in the SC-FCL is qualitatively explained by measuring current distribution among the six strands. The superconducting cable is driven to the normal state strand by strand. Some delay in time is found from the quench of the first strand to that of the last and this is recognized as an I q - t f characteristic in its current limiting performance.

Influence of self-magnetic field on a.c. quench current level of superconducting coils

The a.c. quench current level of a superconducting cable when formed into a coil is, in general, lower than that of a short sample. The current in the coil induces a self-magnetic field on the superconducting winding. It was found from our experiments that the transition from the superconducting state to the normal one in a superconducting coil originates in that part of the winding where the self-magnetic flux density is estimated to be the largest. It is concluded that degradation of the a.c. quench current level in the superconducting coil is mainly brought about by the influence of the self-magnetic field.

Estimation of Total Heat Leak into a Cryostat of Prospective Power Transmission Model System Integrated under Superconducting Environment (PROMISE)

Total heat leak into a cryostat of a “Prospective Power Transmission Model System Integrated under Superconducting Environment” is theoretically estimated to be 41.5W under no load condition. This magnitude is only 0.004% of the transmission capacity of the PROMISE. The heat conduction through current leads is found to take above 98% of total heat leak.

Difference of the Quench Current Level of A Multi-Twisted Superconducting Cable Due to The Direction of The Applied Magnetic Field

The quench current level of a multi-twisted a.c. superconducting cable are measured as a function of the strength of the magnetic field, which is applied in the same, perpendicular or opposite direction to that of the transport current in the cable. The magnetic field applied in the same direction as the current brings about larger decrease of the quench current level than that in the perpendicular direction. However, no change of the quench current level is observed in the case that the magnetic field is applied in the opposite direction to the current.