Abstract
This study presents the influence of various types of nanoparticle (NP) fillers incorporated into a polyurethane (PU) (VUKOL 022) matrix and its subsequent changes in complex permittivity. Two types of surface modification of SiO2 fillers were investigated. The frequency dependence of the real and imaginary parts of complex permittivity was measured within the frequency range of 1 mHz to 1 MHz using the capacitance method. The 1 wt.% NPs in PU caused an increase (MgO, TiO2, n-SiO2, and f-SiO2) or a decrease (d-SiO2) in the real permittivity. The $\alpha $ -relaxation and intermediate dipolar effect were observed at the temperature dependence of the imaginary permittivity. The change in permittivity by various surface modifications of SiO2 and other nanofillers was discussed based on the multi-core model. Moreover, the NPs caused a shift in the local maximum of the permittivity, which was a result of the interfacial polarisation and a charge multiplication of the $\alpha $ -relaxation process.
Highlights
Each high voltage insulation system is a complex system fulfilling various requirements
Within the studied frequency range, the change in complex permittivity was strongly dependent on the frequency and the temperature
Dielectric spectroscopy for the study of PU NCs with various surface modifications of SiO2 and types of NPs as fillers was used. This can help to understand basic issues related to the role of additives, their surface modification, and interactions with a two-component PU matrix
Summary
Each high voltage insulation system is a complex system fulfilling various requirements. In the case of transformers, it can be a solid or a combination of solid and liquid insulating components. There are various materials available for transformer insulation. The commonly used materials are cellulose paper and mineral oil systems in the case of cast-resin dry-type transformers (polyurethane [PU], epoxy, and silicone resin). The electrical insulation is an important part of transformers, helping both to withstand the high electric fields and ensure the loss of heat dissipation. In the case of paper-oil transformers helps the liquid component to dissipate the heat, but at the same time, it creates a potential fire risk. The low thermal conductivity of the electric insulating system of the dry-type transformers creates
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