Optical investigation of high-field conduction and prebreakdown phenomena in a dielectric liquid

The authors report an experimental study of high-field conduction and prebreakdown phenomena in M/DBT (a mixture of mono and dibenzyltoluene) used as a polypropylene impregnant in all-film capacitor technology. Optical and electric measurements were performed simultaneously on the electrically stressed fluid. Electroluminescence of impurities contained in M/DBT has been investigated using a new uniform field electrode arrangement. The light inception stress was determined to be of the order of 20 Vμm_-1 for AC excitation (50 Hz). Configurations with different interfacial situations were studied and exhibited a correlation between charge injection and electroluminescence. Spectral analysis of the light radiated by streamers in M/DBT in a needle-plane electrode geometry revealed the presence of H₂ and C₂ characteristic bands emerging from a continuum corresponding to molecular fragments