Conductivity measurement on thick insulating plaque samples
Sammanfattning: The conductivity is one of the main properties of HVDC cable insulation materials and needs to be evaluated carefully. Since measurement on cables is time consuming, often thin specimens and normal conductivity measurement cells are used to compare the materials. In this way however, the bulk effects will be less represented in the measurement and the results will be less representative. Instead, one needs to perform the measurements on thick plate samples and with higher voltage levels. This work focuses on the conductivity measurements on thick HVDC insulation plate samples subject to a high electric field and carefully controlled conditions. In the literature, there are many different methods of measuring the leakage current such as dielectric spectroscopy, PD, IV and PEA measurements. In this thesis a three electrode setup is used to measure the leakage current where the electrodes are placed inside the oven. This is to be able to control both temperature and high voltage under similar and different conditions where it is possible to change these two parameters during measurement. This was made by two Labview programs; one for creating a schedule and one control program which controls the equipment in the cell. The task was to make sure that the cell functioned by obtaining repeatable and reasonable measurements. The results that were obtained were reasonable and verified that the cell functioned. The executed measurements were performed in order to achieve a better understanding of error factors in the measurement system, ranging from preparing the sample to measuring the leakage current. The purpose with the cell is it to investigate the quality of the HVDC insulation by conductivity measurements on millimetre thick plate samples.
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