Experience in Development of HTS-2 Annular Field Coils for a High-Power Synchronous Generator

NRC Kurchatov Institute - IHEP has developed a technology for the manufacture of annular coils from a second generation high-temperature superconductor (HTS-2 tape). Jointly with the Moscow Aviation Institute, two excitation coils were developed and manufactured from HTS-2 tape in their own cryostats for the synchronous generator model. In doing so, a method was developed for applying to the HTS-2 tape an electric insulation consisting of polyimide film layers with a total thickness of 26 μm. Such insulation provides sufficient electrical strength at a 2500 V voltage with a pressure of up to 5 kg/cm2. At the intermediate stage of manufacture, after the coils had been wound and the shroud applied, the coils manufacturing quality was checked by measuring the coils critical current when immersing them into a liquid nitrogen bath. At the final stage, the coils residing in their own cryostats were cooled with liquid nitrogen in the forced circulation mode. When cooling the coils to the operating temperature, the pressure drop across the cryogenic agent flow was 0.02 MPa, and the cooling time took about 1 h. A limit current value at which stable coil operation will be retained has been found. This current is 116 A and 126 A for the first and second coils, respectively, which is higher than the design operating current when using these coils in the synchronous generator model. An experimental model of a synchronous generator with these HTS-2 coils used as axial field windings was manufactured and tested. During the tests, the generator no-load characteristics, as well as its loading and adjustment characteristics were measured. The test results correspond to the calculated ones.