Electric conductivity measurements including the semiconductor-insulator interface from HVDC cables

Abstract

As global power consumption increases along with increased demands for renewable energy, additional expansions of the existing power grids are required. Extruded HVDC cable systems can be a potent solution to this power transmission problem, both because of its technological advantages allowing for full power flow control as well as its e˙ectiveness compared to HVAC in transporting power over long dis-tances. To ensure reliability and long life time of the extruded HVDC cables, it is of paramount importance to understand fully their characteristics. For this, full scale testing of produced HVDC cables can be performed, but it is time consuming and expensive. Alternatively, small scale testing can be realized on samples of the cable. The purpose of this master thesis was to develop a test set-up for small scale test-ing of cable insulation and to determine the electrical conductivity of insulation material using two types of samples, namely, cable peelings containing insulation-semiconductor interfaces and press-molded plates with comparable geometry. In addition, optical profilometry and microscope studies were conducted along with temperature cycling test to investigate the chosen press-film for the press-molded plates. The performed studies are presented in the report. The test set up was constructed and validated by comparing the measurement results with available data from lit-erature. Furthermore, conductivity measurements were performed with two types of samples for three electric field levels and two di˙erent temperatures (30°C and 70°C). The acquired results were found in a plausible range and were used to identify di˙erences in the conductivities of cable peelings and press-moulded plates. These samples were further analysed with optical profilometry, which indicated no signifi-cant di˙erences in surface texture and roughness between the two di˙erent sample types. From the temperature cycling test, it was concluded that the chosen press-film had no e˙ect on non-monotonic conductivity of the press-molded samples. The performed study broadened understanding of properties of semiconductor-insulation interfaces of HVDC cables.