Breakdown Strength Comparison of Several Fluorinated Liquids with Different Molecular Structures

Fluorinated liquids are used as refrigerants and cleaning agents in various electrical equipment due to their excellent thermal, chemical, and electrical properties. However, the dielectric/insulating properties and breakdown mechanism of fluorinated liquids have not yet been clarified. Therefore, the authors compared the relative permittivity, dissipation factor and breakdown voltage of five fluorinated liquids with different molecular structures: HFE-7100 (C<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf>F<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">9</inf>OCH<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf>), HFE-356mmz ((CF<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf>)<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>CHOCH<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf>), HFE-356mec (CF<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf>CHFCF<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>OCH<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf>), HFC-43-10mee (CF3CHFCHFCF2CF3) and Hexafluorobenzene (C6F6). This paper will help to discuss the effect of different molecular structures on the insulating properties. The relative permittivity and dissipation factor was measured using a liquid electrode and an LCR meter at an applied voltage of 1 V AC, a frequency of 60 Hz, and room temperature. The highest relative permittivity for HFE-356mmz was about 48.1 and the lowest for Hexafluorobenzene was 1.98. Similarly, the highest dissipation factor for HFE-356mmz was 18.621 and the lowest dissipation factor for Hexafluorobenzene was 0.0096. The breakdown voltage (BDV) was boosted at AC 3 kV/s and 15 points were obtained for each sample at 1 mm and 2.5 mm gap. Hexafluorobenzene was found to have a higher BDV than the other samples. From these results, it was found that Hexafluorobenzene, which had a smaller relative permittivity, had a higher BDV. In addition, HFE-7100, HFE-356mmz, HFE-356mec, and HFC-43-10mee, it was considered that bubbles were generated in the samples by Electro Hydro Dynamics (EHD) generated during high voltage charging, and that these bubbles entered between the electrodes, causing the breakdown voltage to decrease.