A Proof of Principle Experiment (POPE) has been constructed and conducted to demonstrate the stability and operation of the SMES conductor in the SMES-WISC team's Engineering Test Model (ETM) design. The experimental facility includes: a 100 kA DC power supply; a 4 tesla, 1 meter bore, background field split solenoid; a three turn-1 meter diameter test coil of the ETM conductoG a dewar for operation of the solenoid and test coil at 1.8 K and 1 atmosphere, and support syskms for vacuum, helium supply and recovery, and data acquisition. The test facility exactly duplicates the electric, magnetic and thermal conditions zxpected for the ETM conductor. We report on measurements of conductor stability vs. transport current, applied magnetic field, and cooling from liquid helium. The measurements characterize the conductor's stability against finite length traveling normal zones, and against quenches resulting from transient normal zones. The data qualify the conductor for dependable use at 50 kA, 4 tesla and 1.8 K.
Abstract-A joint in the superconductor and stabilizer is added to the ETM conductor in the POPE. The joint design is similar to that proposed by Westinghouse for the SMES ETM field joints.Fabrication of the joint is described. Measurements on the performance of the superconducting joint operated in subcooled He II and of the stabilizer joint at 14 K are reported. Measured superconductor joint resistance is 1.6 n o , which agrees with previous analytic calculations. The stabilizer joint RR matches the conductor stabilizer RR. The joint met or exceeded all operational requirements throughout the experiment demonstrating its reliability and small joule heating L INTRODUCTIONThe test coil for the POPE (Proof of Principle Experiment) is three one meter diameter turns of conductor consisting of eight Cu/NbA'i superconducting strands soldered into grooves in the 2.54 cm diameter high purity aluminum (€PAL,) stabilizer, shown in Fig. 1. This cross section is identical to that of the conductor proposed for a larger SMES coil [l]. The total conductor length in the POPE test coil, including the leads, is 11 meters. A schematic layout of the test coil is shown in Fig. 2 In its original configuration, the conductor for the POPE test coil did not have any strand joints. The stabilizer contained one joint, approximately in the middle of its length. This joint was made by flash butt welding of the aluminum prior to inserting the strands into the groove during the initial construction of the test coil in 1989, and has operated well ever since.A full size SMES will contain many stabilizer and strand joints. These joints will be made at the construction site as the coil is being wound, and are thus called "field joints." The proposed field joint consists of a flash butt welded joint in the aluminum stabilizer, and cold upset welds in each of the eight superconducting strands. For each weld the upset material is trimmed away, so that the cross section of the conductor is maintained through the joint area. In general, joints would not be noticeable, except under close visual inspection. Since the conductor is immersed in a helium bath, there are no cryostat or conduit joints that must coincide with the conductor joint.A failure in the positive lead of the POPE test coil occurred in August 1993. The failure occurred due to current being applied during a RR test at 15 K for an excessive period of time. The aluminum conductor and superconducting strands melted in a section of the positive lead at the location shown in Fig. 2. This failure required a rapid fix in order to finish the POPE testing on schedule and presented the opportunity of testing a repair similar to the proposed field joint in a large SMES.The POPE test coil is repaired in one month, allowing completion of the test program on schedule. Despite tight schedule and significant technical constraints caused by the nature of the in-situ repair, a satisfactory joint is produced. In this report, we describe the fabrication and performance of this joint. Through this effort, we...
In large He I1 superconducting applications, reliable transition leads are needed to transfer large currents from4.2 K He to He II(Tc2.17 K). The lead consists of a plug made of alternating cu/ss thin laminates with attached s/c strands. The laminates minimizes thermal conduction from 4.2 K to He I1 and provide large heat capacity for protection compared to solid ss transition. We have constructed and tested a 50 kA transition lead that is fully stable up to about 35 kA. Between 35 and 55 kA, the lead will have a stable temperature profile if it becomes normal. Between 55 and 75 kA, its temperature will increase slowly enough with time (following a disturbance) so the protection circuit can turn off the connected power supply.
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