Presentation Information
[APP1-15]Progress of AC inductive energization test of high-temperature superconducting assembled conductors under liquid hydrogen cooling
*Ken Shimada1 (1. Kwansei Gakuin University (Japan))
Keywords:
High temperature superconductor,Assembled conductor,Inductive energization,Liquid hydrogen
The objective of this study is to conduct a 6 kA-class AC inductive energization test of assembled conductors under liquid hydrogen cooling and an external magnetic field of 5 T. The preliminary study entailed the testing of single-layer assembled conductors under liquid nitrogen and liquid hydrogen cooling. A single-layer short-circuited conductor was fabricated by winding four REBCO wires with a pitch of 25 mm around an 8.6-mm-diameter former. The conductor was wound onto a 144-mm-diameter FRP frame located within the upper primary coil. Subsequently, it was short-circuited at both ends after being routed through the lower external magnetic field coil (Figure 1). The primary and external magnetic field coils were composed of four stacked REBCO double-pancake coils with an inner diameter of 130 mm and an outer diameter of 206 mm, and approximately 444 turns). AC inductive energization tests under liquid nitrogen cooling were conducted by applying AC at 0.5–4 Hz to the primary coil. The Rogowski coil voltage was measured using a high-speed logger, and the magnitude and phase of the secondary current were calculated. The secondary current showed a proportional increase with the primary current (induction ratio: 347), yet the induction ratio underwent a gradual decline. The phase of the Rogowski coil voltage showed a precipitous decline when the peak value of the primary current reached approximately 1.48 A. At this point, the peak value of the secondary current was 513 A, which was nearly equaled the total Ic of the four REBCO wires (512 A). Additionally, the establishment of a distortion index for the Rogowski coil voltage waveform facilitates more precise identification of the secondary conductor’s Ic.Subsequently, an AC inductive test at 1 Hz was conducted under liquid hydrogen cooling. The induced current shows a proportional increase with the primary current, attaining a maximum peak value of 5,948 A (Figure 2). During this process, no distortion was observed in the Rogowski coil voltage waveform, and the phase remained nearly constant at 90°. Subsequent increase in the primary current resulted in the distortion of the Rogowski coil voltage waveform. This distortion had affected the primary current waveform, ultimately resulting in power supply shutdown. The maximum secondary current peak value of 5,948 A was approximately 1.06 times the predicted conductor’s Ic (5,632 A) at 20 K. In addition, similar inductive energization tests were conducted under an external magnetic field of approximately 0.7 T. A decline in induction ratio was detected after the test, which is attributed to conductor degradation caused by electromagnetic forces. Improvements to the test specimens will be made for the final AC inductive energization tests under higher external magnetic fields.