Inclined plane initial tracking voltage for AC, +DC and -DC

The tracking voltage in the inclined plane test with AC is compared to the tracking voltage with DC, using the initial-tracking-voltage test method as per ASTM D2303 and a proposed coefficient of variation parameter. The severity of DC, as opposed to AC voltage, on RTV silicone rubber materials is confirmed using both strategies, where +DC is found to be the most severe voltage. The leakage current waveforms are found to consist of two components corresponding to wetting of the surface and to dry-band arcing. The mean value of the leakage current is a reflection of the wetting of the surface; whereas, the leakage current variation is a reflection of the dry-band arcing. Accordingly, a coefficient of variation parameter is proposed as an indicator of the relative severity of the dry band-arcing. Employing this coefficient of variation parameter, the ratios of the equivalent +DC and -DC to AC initial-tracking voltage are attained for 30 wt% silica filled two-part RTV silicone rubber. The results obtained using the coefficient of variation parameter have been verified experimentally using the initial-tracking-voltage in ASTM D2303.