Assessment of the Resistance of Mica Insulation to Interlayer Discharges

The breakdown of a layered composite mica insulation systems of the stator windings consists of two stages of discharge development - a normal discharge and interlayer discharges along the insulation layers (treeing). The existence of interlayer discharges leads to accelerated development of the defect (longitudinal cavities or places of weak adhesion of the insulation layers) and the formation of a channel for incomplete breakdown of the insulation system. In this work, we used the method of initiating interlayer discharges using an artificial defect in the form of a cylindrical recess. The defect imitated the damage caused by the normal discharge. Flat model specimens made by Resin Rich technology with defects of different depths were used for testing This method allows obtaining statistically reliable values of the insulation life for comparing various versions of layered mica-containing insulation with a small area of samples.