Analysis of a Joint Method Between Superconducting YBCO Coated Conductors

112

HTS synchronous generators, in which the rotor coils are wound from high-T c superconducting wire, are exciting attention due to their potential to deliver very high torque and power densities. However, injection of the large DC currents required by the HTS rotor coils presents a technical challenge. In this paper we discuss the development of a brushless HTS exciter which operates across the cryostat wall to inject a superconducting DC current into the rotor coil circuit. This approach fundamentally alters the thermal load upon the cryogenic system by removing the need for thermally inefficient normal-conducting current leads. We report results from an experimental laboratory device and show that it operates as a constant voltage source with an effective internal resistance. We then discuss the design of a prototype HTS-PM exciter based on our experimental device, and describe its integration with a demonstration HTS generator. This 200 RPM, 10 kW synchronous generator comprises eight double pancake HTS rotor coils which are operated at 30 K, and are energised to 1.5 T field through the injection of 85 A per pole. We show how this excitation can be achieved using an HTS-PM exciter consisting of 12 stator poles of 12 mm YBCO coated-conductor wire and an external permanent magnet rotor. We demonstrate that such an exciter can excite the rotor windings of this generator without forming a thermal-bridge across the cryostat wall. Finally, we provide estimates of the thermal load imposed by our prototype HTS-PM exciter on the rotor cryostat. We show that duty cycle operation of the device ensures that this heat load can be minimised, and that it is substantially lower than that of equivalently-rated conventional current leads.

Section: Excitation Of Hts Coils Using a Rotating Hts Flux Pumpmentioning

confidence: 92%

Development of a brushless HTS exciter for a 10 kW HTS synchronous generator

Bumby

Badcock

Sung

et al. 2016

112

“…To guide our work on laser slotting, we developed a 2D finite element analysis (FEA) model, to analyze the current flow between two tapes in contact with each other. A similar numerical method has been validated to have an acceptable accuracy [31]. We calibrated the model by matching the numerical and measurement results in a parametric sweep study.…”

Section: Laser Slotting To Reduce Contact Resistivity Between Two Reb...mentioning

confidence: 99%

Current sharing in double-sided REBCO tapes

Xue,

Li,

Zhu

et al. 2024

Current sharing between RE-Ba-Cu-O (REBCO, RE=rare earth) tapes within a high-temperature superconducting (HTS) coil or cable is important to avoid damage from uncontrolled quench of superconducting devices operating at high currents. Current sharing between REBCO tapes is found to be limited by contact resistivity between the adjacent tapes, which is about 20x higher in the REBCO-facing-substrate (face-to-back) configuration that is commonly used in devices compared to a REBCO-facing-REBCO (face-to-face) configuration. Double-sided REBCO tapes always offer face-to-face contacts between adjacent tapes, and this benefit for excellent current sharing has been validated in experiments wherein an artificial defect is introduced in one tape in a 2-ply tape stack. Additionally, current sharing between the two REBCO layers within one double-sided REBCO tape has also been investigated. Slotting of the double-sided tapes, wherein slots through the insulating buffer stack are filled with a conductive material, has been found to significantly enhance the current sharing from one REBCO layer to the opposite layer.

“…It is known that the most straightforward way to make a joint between high-temperature superconducting REBa 2 Cu 3 O 7−δ (RE123)-coated conductors is to use solder between the conductors. However, this typically has a joint resistivity above 10 −8 Ω • cm 2 at 77 K [1,2], due to high interface resistance between the silver protection layer and the RE123 layer [3]. It is unlikely that such a joint can provide a persistent current sufficient for NMR and MRI measurement, which requires a joint resistivity below 10 −12 Ω • cm 2 [4].…”

Section: Introductionmentioning

confidence: 99%

Development of a superconducting joint between a GdBa₂Cu₃O_7-δ-coated conductor and YBa₂Cu₃O_7−δbulk: towards a superconducting joint between RE (Rare Earth) Ba₂Cu₃O_7−δ-coated conductors

Jin¹,

Yanagisawa²,

Maeda³

et al. 2015

We have started to develop a superconducting bridge joint between two GdBa2Cu3O7−δ (Gd123)-coated conductors, where both conductors are placed in an end-to-end arrangement on the surface of a melt-textured YBCO (including Y2BaCuO5 and YBa2Cu3O7−δ) bulk, which acts as a superconducting medium between the coated conductors. As a first step in the development, one half of the bridge joint assembly was modeled and investigated. Experimental results achieved are as follows: (a) the higher-melting-temperature textured Gd123-coated conductor acts as a seed for the melt texture of the YBa2Cu3O7−δ (Y123) bulk, and (b) the superconducting phase continues across the Y123/Gd123 boundary. The critical current of the joint model is 10 A, which is about 10% of the original Gd123-coated conductor, at 77 K in a self-magnetic field. These results are considered to be extensible to the superconducting bridge joint between the Gd123-coated conductors.