Chapter 166 - Fabrication and characterization of Bi-2223 coils for generator applications

Abstract

This chapter investigates a set of race-track pancake coils for a 100 kVA superconducting generator, which is constructed using high strength reinforced Bi-2223 tapes with co-wound fiber glass cloth and epoxy impregnation. Mechanical and thermal properties of the coil composites are conducted. I-V characteristics and the critical current at 77 K of the superconducting coils are measured. The onset and progress of thermal runaway due to over-current are investigated by measuring the temperature rise and overall voltage increase. The choices of impregnation and insulation materials and matching thermal contractions of the coil components are crucial for reliable performances of the coils. The coils show a constant performance after several cooling cycles with critical currents in the range of 75 ± 3 A. The proof and ultimate axial tensile strength are 290 MPa and 360∼390 MPa, which indicate satisfactory strength for safe operation of the 100 kVA superconducting generator. The results of this work are crucial for modeling and predicting performances during operation of the generator and also represent a mean of quality control to qualify the coils for use in the machine.