Status of high transport current ROEBEL assembled coated conductor cables

Abstract

Assembling coated conductors (CC) into flat ROEBEL bars (RACC cable) was introduced in 2005 by the authors as a practicable method of reaching high transport currents in a low AC loss cable, which is a cable design suited for application in windings. The transport current of 1.02 kA in self-field at 77 K achieved so far, however, is still too low for several applications in electrical machinery such as larger transformers and generators/motors. A new cable concept for further increased currents was presented just recently. The goal of the new design was primarily to demonstrate the possibility of strongly increased transport currents without changing the important cable features for low AC losses. such as, for example, the transposition length of the strands. We present detailed investigations of the properties of this progressed cable design, which has threefold layered strands, an unchanged transposition pitch of 18.8 cm and finally the application of 45 coated conductors in the cable. A 1.1 m long sample (equivalent to six transposition lengths) was prepared from commercial Cu stabilized coated conductors purchased from Superpower. The measured new record DC transport current of the cable was 2628 A at 77 K in self-field (5 μV cm −1 criterion). The use of three slightly different current carrying batches of strand material (±10%) was a special feature of the cable, which allowed for interesting investigations of current redistribution effects in the cable, by monitoring a representative strand of each batch during the critical current measurement. Although current redistribution effects showed a complex situation, the behaviour of the cable was found to be absolutely stable under all operational conditions, even above the critical current. The high self-field degradation of the critical current reached the order of 60% at 77 K, and could be modelled satisfactory with calculations based on a proven Biot-Savart-law approach, adapted to the specific boundary conditions given in this new cable design.

Superconducting Materials and Conductors: Fabrication and Limiting Parameters

“…A major obstacle to the application of YBCO in HEP magnets is that it is difficult to form a transposed cable that enables currents in the tens-of-kA region. Roebel-type cables are considered [133][134][135], but are still in their relative infancy. Recent tests at CERN on two Roebel cables made by Karlsruhe Institute of Technology (KIT) and General Cable Superconductors (GCS), assembled from 10 and 15 12-mm-wide tapes respectively, showed critical current at 4.2 K in excess of 10 kA in a parallel 10 T background field, and approximately 4 kA in a 10 T perpendicular field [136].…”

Magnetization Losses of Roebel Cable Samples With 2G YBCO Coated Conductor Strands

“…LTERNATIVE CABLING technology is required for constructing cables with transposed strands using high temperature superconducting (HTS) flat tapes, a necessary geometry for attaining high critical current density by texturing Roebel cables [1], originally invented more than a hundred years ago for reducing ac loss in conventional machines, is a promising configuration which have received considerable research and development effort for adapting to HTS conductors [2][3][4]. While the initial driver for HTS Roebel cables has been the reduction of hysteretic loss in superconductors for power applications, interests in future high field accelerators beyond the Large Hadron Collider (LHC) have brought new impetus and prospects.…”

Advances in the Development of a 10-kA Class REBCO Cable for the EuCARD2 Demonstrator Magnet

“…4, is based on punched tapes, assembled in a compact configuration inspired by the high current transposed conductors used in electrical machinery [51], [52]. The Roebel cable has the advantage of a relatively compact configuration, it does not require bending of the tapes, it is flexible, and the tapes are transposed with respect to the external field.…”