Electrical and thermal behaviour of electrical joints with normal- and superconducting materials at low temperatures

Abstract:
Due to the further development of metal coated, thin film high temperature superconductors (HTS) which operate at the temperature of boiling liquid nitrogen (LN2, -195.8 °C) a wide field of application in superconducting fault current limiters, generators or motors arises. In order to apply HTS in these devices, electrical joints between normal- and super-conducting materials as well as joints between HTS are needed. To develop and evaluate these electrical joints it is necessary to measure and investigate the electrical (e. g. contact resistance, power loss) and thermal behaviour of the conductors themselves and their joints at the temperature of LN2. Therefore a low temperature test rig was built up. The given paper presents the design, mounting and implementation of the test rig. The design of tapping the potential and the arrangement for measuring the voltage as well as the calibration and fixation of thermocouples are described. At first the different conductors are measured. In a second step, electrical joints with normal- as well as with superconductors are made. Different techniques of establishing an electrical joint will be considered in the tests and evaluated according to their usability at low temperatures. All results are compared with reference measurements at room tempera-ture.