Investigation of polarization processes

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Supervisor:
Dr. Tamus Zoltán Ádám
Department of Electric Power Engineering

In this study the temperature dependence of the various time constant polarisation processes was investigated. The measurements were carried out on new and aged, square-shaped, 0.5mm thick PVC specimens containing four different amounts of plasticizer by means of the advanced response voltage method.

In addition to the temperature dependence, the plasticizer and aging dependence of the polarisation processes, as well as the thermal and plasticizer dependence of conductivity and polarisation conductivity were also investigated. Hence, the measurements to determine the temperature dependence of the polarisation processes were carried out in three different temperatures (55°C, 40°C, and 24°C) before and after the aging process. The purpose of the aging process was to reduce the plasticizer content of the PVC insulations by 20%; however the measurements suggested significantly bigger decreases. Thermal degradation was chosen as the degradation type.

The research had revealed that by increasing the amount of plasticizer, the conductivity of the insulation increases. This result was also verified by the Arrhenius plots of the initial slopes of the decay voltage. It was determined that by means of the initial slopes of the return voltages, not only could the shifting of the polarisation spectrum to the left as the temperature increased be demonstrated, but also whether the state of the polymer was below or over the glass transition temperature at the given temperature. As the result of my research I suggested that the plasticizer content of PVC insulations can be differentiated by means of their polarisation conductivities. This result was verified by the Shore D hardness measurements.

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