In this study, we present the results of the influence of surface modification of TiO2 nanoparticles on the short-term breakdown strength and space charge distribution of low-density polyethylene (LDPE). A polar silane coupling agent N-(2-aminoethyl) 3-aminopropyl-trimethoxysilane (AEAPS) was used for the nanoparticle surface modification. Despite agglomeration and a poor interface compared to untreated nanoparticles, it was found that the incorporation of polar groups onto the nanoparticle surface improved both the dielectric breakdown strength and space charge distribution as compared to samples filled with untreated nanoparticles. Microstructure studies showed that the presence of polar groups on the TiO2 nanoparticle surface did not evidently affect the degree of crystallinity, crystalline morphology (except for internal spherulitic order), and chemical structure of the polymer matrix. The improved dielectric breakdown strength was therefore concluded to be directly due to beneficial effects related to the variation of the electrical features at the particle surface due to introduction of polar groups. For the same reason, with the use of surface modified nanoparticles, formation of space charge was suppressed.

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Interfaces between solid insulating materials are critical in high voltage apparatus. In this work a test cell was designed for measuring tangential breakdown strength of an interface between insulating rubber and silicone gel. The test cell comprised two disc-shaped electrodes with a rubber cylinder pressed between them. The electrodes and the rubber cylinder were cast in silicone gel thus creating the rubber-gel interface. The test cell was used to measure breakdown voltage (AC) of rubber-gel interfaces on 19 samples. In 14 of the tested samples the breakdown occurred at the rubber-gel interface whereas in the remaining five samples the breakdown occurred in the bulk gel or inside the rubber cylinder.