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Cryogenics, Volume 52, Issues 4–6, April–June 2012, Pages 310-314
H. Rodrigo, F. Salmhofer, D.S. Kwag, S. Pamidi, L. Graber, D.G. Crook, S.L. Ranner, S.J. Dale, D. Knoll
Center for Advanced Power Systems, Florida State University, 2000 Levy Avenue, Tallahassee, FL 32310, USA
Southwire Company, One Southwire Drive, Carrollton, GA 30119, USA
Abstract
High-temperature superconductors (HTS) allow powercables of substantially higher current
density than conventional copper or aluminum cables. This is important for applications where a low mass and a low volume are critical such as naval, aeronautical and space applications. The novel type of cable under consideration is cooled by gaseous Helium at elevated pressure. Helium is known for having poor electric breakdown strength; therefore the dielectric capabilities of this type of cable must be tested under conditions similar to the envisaged operation. In order to study the dielectric performance we have designed and built anovelhighpressure cryostat rated at 2.17 MPa which has been used for testing model cables of lengths of up to 1 m. The cryostat is an open system where the gas is not re-circulated. This allows maintaining ahigh purity of the gas. The target temperature range is between 40 K and 70 K. This substantially increases the critical current density of the HTS compared to 77 K, which is the typical temperature of cablescooled by liquid Nitrogen. The cryostat presented allows for adjusting the temperature and keeping it constant for the time necessary to run a complete dielectric characterization test. We give a detailed description of the cryostat. Measurements of partial discharge inception voltages as well as the temperature distribution along the model cables as a function of time are presented. Tests showed that the thermal insulation characteristics of this cryostat were sufficient for the dielectric tests of up to 1 h duration. The partial discharge inception voltage (PDIV) of the high voltage bushing was about 16 kV. These values are well within our design requirements.
