Proposta de configuração para testes e caracterização de dielétricos em condição criogênica para uso em tecnologia de supercondutores

Abstract

One of the most important issues in the development of cold dielectric superconducting power cables (CSE), as well as other high critical temperature superconducting technology (HTSTec) devices, is the electrical insulation system in a cryogenic environment. It is desirable to measure both the dielectric strength, dielectric losses and electrical permittivity of insulating materials at cryogenic temperatures. Although there are measurements of these characteristics in a cryogenic environment for some materials, there is still a lack of methodologies and apparatus specific to this field of research, which would allow further studies with new material proposals and the availability of data for projects. In this thesis work we present a contribution through the design of a measurement system that allows measuring the three quantities mentioned in samples of dielectric materials at liquid nitrogen bath temperature (77 K), industrial frequency and high voltage, using unequal electrodes (25/ 75mm). This system uses the same electrodes and cryogenic chamber for all measurements, complying with national and international standards. Therefore, only the external power supply and measurement circuits must be changed to carry out the respective characterization. Initially, the arrangement was designed with the help of computer simulation, using commercial finite element method (FEM) software, and design considerations. In a subsequent stage, assembly and a concept test of the proposed equipment were carried out, where measurements of the dielectric properties mentioned were made on sheets of laminated NKN dielectric material. This material is composed of polyimide film wrapped in two layers of aromatic polyamide, which was proposed as an alternative in the first Brazilian CSE project. Dielectric strength measurements were also made with equal electrodes (6.4/6.4 mm), electrical permittivity and loss tangent at low voltage, using an LCR meter (inductance, capacitance and resistance). In this case, the measurements were at room and cryogenic temperatures, involving the NKN itself and its constituents. Results obtained with the concept test are compared with these measurements and others available in the literature. The proposed equipment concept is functional, even for a relatively simple arrangement, and could be used in different contexts. New measurements and improvements are expected in future proposals.