Characteristics of microsecond-pulse surface flashover on epoxy resin surfaces in SF6

Surface flashover on insulating materials is likely to occur in composite apparatuses in overvoltage situations. In order to investigate the surface characteristics of epoxy resin (EP) materials, before and after flashover, microsecond pulses were applied to simulate transient overvoltage situations in a power system. Within the SF6 filled experimental chamber, pulse voltages with a frequency of 5 Hz and an amplitude of 25 kV were applied to induce surface flashover. The flashover characteristics of EP under different SF6 pressures were subsequently determined. The results show that the flashover voltage increases with increasing SF6 pressure. In addition, atomic force microscopy, scanning electron microscopy, and X-ray energy dispersive spectroscopy were performed to explore the morphology and elemental content of the material surfaces. During aging treatment, granular bulges were generated on the surface of the materials. With increasing treatment time, bulges first gathered and then became larger. Then, they became flattened as a result of burning due to electrical arcing. Thus, the surface roughness increased at first and then decreased. The material surface sequentially evolved into crack, granular, flocculent-granular, and then flocculent zones during the aging process, and these zones were distributed symmetrically in the aging area. Moreover, a large amount of flocculent substances (consisting of carbon and carbon compounds) accumulated near the electrodes. The insulating performance of the material surface was impaired by the aging treatment, which can be attributed to the combined effects of change in surface roughness and the discharge channel generated by surface carbonization.

1 Introduction

As a composite insulating material, epoxy resin (EP) is widely used in power systems, especially in high-voltage composite apparatuses such as gas insulated switchgear (GIS). As the voltage level in such power systems rises, the demands placed on the insulating performance of EP also increase. Therefore, different types of EPs have been produced and applied to different parts of high-voltage electrical devices. At present, GISs are designed to be small but powerful, placing even higher demands on the insulating performance of the epoxy resins within [1]. Moreover, in high-voltage composite apparatuses, the decomposition of SF₆ (and other insulating gases) caused by partial discharge can generate HF, H₂S, SOF₂, and other corrosive gases [2]–[5]. This results in a certain amount of aging in the insulating materials. Thus, the insulating materials in composite apparatuses need to meet new demands. The basin insulator fillers used in currently produced GISs have also been improved, from the originally used silica, to alumina which has stronger corrosion resistance [6]–[7].