Eight different types of joining between two parallel high Tc superconducting (HTS) tapes were prepared and current-voltage ( -) characteristic curves were investigated at 77 K, liquid nitrogen temperature. Contact resistances of joint parts with 25 mm in length were estimated from -curves. Lowest contact resistance among eight samples having different types of joining was 0.497 . The best joining method is to do crossly joining with HTS tapes on two parallel HTS tapes after filling solder paste into their gap. In this case, lowest joint resistance was 0.15 at 77 K and 0.05 at 28 K. Joule heat of a joint sample generated at 30 K and at 100 A was calculated 0.492 mW. Also, in -curve of samples crossly joined with HTS tapes, it was found that joint resistance does not depend on variation of magnetic fields (0 7000 G) at 77 K. From consideration of Joule heat generation, such joining method is available for fabricating the field winding of superconducting rotating machine.
To make a superconducting coil by winding a High Temperature Superconductor (HTS) tape conductor on a bobbin, the double pancake winding technique is widely used to reduce number of splicing contacts between conductor pieces. However, this makes some (critical current) degradation on kink points of the conductors, which is unavoidable. Soldered double pancake can be an alternative way to overcome the degradation. This paper describes and compares the two ways of winding; usual double pancake, and soldered double pancake. Characteristics of the windings are measured and compared. The soldered double pancake winding has resistance on the contact points, but the estimated Joule heating on the contacts is much smaller than heat leak of cryostats.Index Terms-Bobbin contact, contact resistance, HTS tape, soldered double pancake winding.
A 3-phase, 100 hp, 4 pole, 1800 rpm superconducting synchronous motor built and tested in Korea Electrotechnology Research Institute(KERI). This machine consists of HTS rotor and air-core stator. The HTS field windings are composed of the double-pancake coils wound with AMSC's stainless steel-reinforced Bi-2223 tape conductor. These were assembled on the support structure and fixed by a bandage of glass-fiber composite. The cooling system is based on the heat transfer mechanism of the thermosyphon by using GM cryocooler as cooling source. The cold head is in contact with the condenser of a Ne-filled thermosyphon. The rotor assembly was tested independently at the stationary state and combined with stator. The open circuit, no-load, and short circuit characteristic were obtained. Also, load tests in motor mode driven by inverter and generator mode connected to resister load bank were conducted. This paper will present design, construction, and experimental test results of the 100 hp HTS machine.
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