YBCO Coated Conductor Interlayer Electrical Contact Resistance Measured From 77 K to 4 K Under Applied Pressures up to 9.4 MPa
Shengchen Xue, M.D. Sumption, E. W. Collings
Abstract
The inter-tape resistance is a key parameter for REBCO coated conductors, cables, and coils for various applications. We explored the transverse resistance for sets of REBCO tape stacks, measured in a “through-the-stack” configuration. For the first measurements (Rig 1), the stacks were cooled to LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> temperature and the tape stack resistance was measured as a function of applied pressure (i.e., the pressure was applied during the measurement) up to 417 kPa. We analyzed these direct measurements to examine the contributions of the tape surfaces vs the internal tape contributions, and the results were translated into a contact efficiency, η, defined as η = R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> *A <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> (the contact resistance * contact area). It was found that the electrical contact efficiency, η, for an un-pressurized stack was ≅ 0.934 Ω·cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , but was reduced by a factor of 8 under 417 kPa of pressure to η ≅ 0.111 Ω·cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . A second test rig was used to explore tape stack resistances from 4.2 K - 77 K. This rig allowed pressures of up to 9.94 MPa to be applied. Here, the pressure was first applied, and then the sample was cooled. This difference between Rig 1 and Rig 2 allowed us to compare the protocols of fixed pressure (Rig 1) and fixed constraint (Rig 2). The contact efficiency reached 178 μΩ·cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at 4.2 K and 232 μΩ·cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at 77 K.