AC corona resistance performance of silicone rubber composites with micro/nano silica fillers

Silicone rubber (SR) insulating surfaces are often subjected to corona partial discharges (PD) during outdoor operation which can change the surface chemistry significantly and result in considerable surface deterioration, hydrophobicity loss, and enhancement of PD activity. In this work, the effect of micro and nano-fillers addition on surface degradation of SR under AC corona discharge is examined by analyzing the PD characteristics, hydrophobicity and surface morphology. Nano precipitated silica and ground silica with particle size of ~20 nm and ~5 μm are adopted and incorporated in RTV silicone rubber by two different mixing techniques. Mechanical stirring followed by ultrasonic water bath are applied to achieve uniform dispersion of fillers in RTV SR matrix. The four different types of the composite, i.e. pristine SR, 30-wt% micro-silica/SR, 27.5-wt% micro with 2.5-wt% nano-silica/SR and 5-wt% nanosilica/SR composites are tested under AC corona discharge. It is found that, at the end of ageing, the nano-silica composite showed the best suppression against PD activity and higher resistance against surface damage as compared to other test samples. It is also found that resistance to hydrophobicity loss is offered by composites during the initial 48 h of corona treatment but it is completely lost at the end of 96 h of ageing.

I. Introduction

Utilization of silicone rubber (SR) composites for outdoor insulation in high voltage power system apparatus is increasing due to their better electrical, chemical and physical characteristics as compared to glass and porcelain insulators [1]. However, SR composite insulators are of organic nature and thus they are prone to degradation caused by complex environment and partial discharge activities. There are various causes of degradation of SR insulators in outdoor environment but corona discharge is a prime reason behind gradual deterioration of composite insulators in operation [2]. Hillborg et al. [3] had investigated the hydrophobicity loss and recovery mechanism of PDMS after corona treatment. Earlier, researchers concentrated on the degradation mechanism of SR due to corona discharges under different air pressure by investigating the hydrophobicity loss and recovery characteristics [4]–[5]. Moreno et al. [6]–[7] introduced a single pin to ground plate electrode configuration to investigate the impact of long term corona on degradation of EPDM, SR and their blend. Liang et.al [8]–[9] reported the impact of corona on hydrophobicity loss and corona exposure durations on hydrophobicity recovery characteristics of HTV SR. Recently, Iyer et.al [10] reported significant improvement in corona resistance of epoxy filled with micro + nanofiller compared to micro and unfilled epoxy. It was also reported that AC and DC corona resistance of SR can be enhanced by adding small amount (3wt %) of fillers [11]–[12].