Enhancement of DC Flashover of Liquid Silicone Rubber by Direct Fluorination

Liquid silicone rubber (LSR) sheet samples of a commercial formulation and surface fluorinated using a F₂/N₂ mixture at various temperatures are studied in this work. The intrinsic DC flashover of the surface fluorinated samples is evaluated using a sheet sample/finger electrode configuration and under a stepwise increasing voltage. The tests show an increase up to 64% in the intrinsic DC flashover voltage of the LSR by the fluorination and an influence on the flashover on the fluorination temperature. ATR-IR and XPS analyses indicate that there are Si-F bonds as well as C-F bonds in the fluorinated layers. SEM shows the thickness of the fluorinated surface layers with nanostructured surfaces. Surface conductivity and potential decay measurements reveal that the fluorination caused a large increase in surface conduction, in association with fluorination temperature. The improvement in the intrinsic DC flashover is mainly attributed to the suppression of surface charge accumulation on the LSR by the increased surface conduction.

1 Introduction

High voltage direct current (HVDC) transmission has many advantages and has become an attractive alternative to high voltage alternate current (HVAC) transmission. The increasing use of renewable energy sources also needs DC transmission to interconnect power networks. However, the design of HVDC systems with the same reliability as HVAC systems remains a challenge. One of the main concerns for HVDC is that there is charge accumulation in insulators or on insulators, which will cause electric field distortion, accelerate insulation degradation, and even lead to insulation breakdown or flashover [1]–[3].