Spectroscopic observations of light emission from surface flashover of insulators under high voltage stress

Spectroscopic investigations of the prebreakdown and breakdown luminescence of a dielectric surface under the application of a high-voltage pulse were performed in vacuum ambience on polycrystalline alumina. Information about the composition of the light emission was obtained with the aid of a 2D CCD (charge coupled device) camera interfaced with a flat field spectrometer. Time-resolved studies of the light emission were also done using two PMTs (photomultiplier) tubes with spectral response in the UV and visible region. The surface of the insulator was treated with different polishing media like silicon carbine discs and diamond paste in order to understand the role played by the surface microstructure of the sample. The results reported indicate that the surface treatment of a dielectric plays a very important role in the electrical performance of the insulator. In addition, it is evident that there are significant differences in the spectral nature of the light emission that can be observed from the spectrum of surface flashover from a SiC polished sample compared to that of an unpolished sample. A correlation between the electrical performance of the insulator and the development of the spectral nature of the light emission is indicated. All these interesting and important observations are being investigated in an extensive manner. The important role played by material defects and desorbed gases in the pre-breakdown phase of the surface flashover events are again confirmed