Spark Discharge Inception Voltage under Surge Voltage Application Influenced by Air Gap Length

Inverter fed-motors in the industrial field are commonly used due to high controllability and high efficiency. The inverter fed-mothers are being downsized to reduce the costs. The electrical insulation system in motors is repetitively subjected to further high electric field, and a partial discharge easily occurs under further high field at an air gap between motor windings. The air gap length-defendant spark discharge inception voltage under the surge voltage application (Surge-SDIV) was measured to apply the date to the analysis of the partial discharge characteristics. The Surge-SDIV was higher than that under DC voltage application (DC-SDIV). The difference between the SurgeSDIV and the DC-SDIV increased with the increase of the air gap length. The discharge delay time of the Surge-SDIV also increased with the increase of the air gap length. These are attributed to the appearance probability of the initial electron or the development probability of the electron avalanche under the surge voltage application, or both of these.