Effect of Joint Quality on Conductor Short Sample Performances
Full size conductor short samples for the International Thermonuclear Experimental Reactor (ITER) are composed of two straight bars connected together at one end, and to the facility current leads at the other ends. The quality of these electrical connections was early suspected to play a role in the measurement of the conductor performances, which has been confirmed by recent test results. In order to investigate this phenomenon, CEA developed an experimental program, within EFDA task ELRES, to study the effect of well calibrated joint defaults on conductor performances. The experiments were carried out on subsize (108 strand cable-in conduit) NbTi conductors. The paper reports on the results of the effect of 25 per cent and 50 per cent unconnected length of cable in the joints, with respect to a perfect joint in which the effective connected length is 100 per cent of the final cable twist pitch length. Two types of NbTi strands (with internal CuNi barrier or with Ni plating) associated with two different cable void fractions (36 or 32 per cent) were used in order to vary the interstrand resistances. Five samples were extensively tested in current sharing temperature experiments with current up to 6 kA, under magnetic field up to 3.4 T. Each sample is composed of two identical bars except the strands used in the bars are different. Only the inter-conductor joint is affected by a default. Experimental results clearly show that joint defaults degrade measured conductor critical currents, except when sufficiently low interstrand resistances allow a possible current redistribution among the strands (particularly in the joint). The use of a wide range of interstrand resistances, directly measured on spare samples and confirmed by AC losses measurements, enables us to draw quantitative conclusions. Results of the analysis of Hall probe signals showing evidence of current redistribution among strands during the experiments are also presented in the paper.
Bibliographic Reference: An oral paper given at: 7th European Conference on Applied Superconductivity Organised by: Vienna University of Technology, Vienna (AT) Held at: Vienna University of Technology, Vienna (AT)
Availability: Available from Association EURATOM-CEA, Département de Recherches sur la Fusion Contrôlée, CEA Cadarache, F-13108 St Paul-Lez-Durance, France Tel: (+33) 4 42 25 70 01; Fax: (+33) 4 42 25 64 21 E-mail: email@example.com
Record Number: 200518356 / Last updated on: 2005-10-04
Original language: en
Available languages: en