Measurements of electroluminescent performances of silicon carbide coatings for stress grading of HV electric machines

In order to optimize the design of the stress grading structure for the end-windings of high voltage (HV) electric machines, a suitable and convenient method for accurate measurement of potential gradient became significant. In this paper, a non-contact measuring setup was firstly established to detect the electroluminescent performances of SiC tapes/coatings at high DC, AC and impulse voltages. Three kinds of SiC tapes/coatings with the different non-linear conductivities were prepared. The electroluminescence spectra for the primary SiC tapes under different DC voltages were measured by using a fluorescence spectrophotometer. The influences of applied high voltage waveforms and insulating resin impregnating treatment on the electroluminescent performances of SiC tapes were carried out, respectively, by means of photomultiplier probe. The measured results indicated the peak wavelength of electroluminescent was near 465nm for measured three SiC tapes. It was found the electroluminescence intensities of SiC coating, formed by insulating resin impregnating treatment, decreased greatly. The obtained relationship of electroluminescence (luminous) intensity of SiC tape with applied DC electric field could be fitted with different formulas for three measured SiC tapes. The waveforms of voltage output signals corresponding to the electroluminescence intensities of the SiC coating samples were observed under AC and impulse electric fields. The measured electroluminescence intensity of SiC coating at a 1.2/50 microsecond impulse electric field performed with a waveform of 14/77 microsecond. The electroluminescence waveforms of SiC tape/coating are much different from the waveforms of applied alternating electric fields.