The Effect of Discharge Activity on the Performance of Corona-Protective Semiconducting Coatings of the Stator Bar Insulation

The work is focused on the study of discharge processes in the corona protection system of rotating machines. A resistance decreasing of the semiconductor coating along with the occurrence of mechanical vibration leads to the appearance of discharge activity in the stator slot. Under the action of vibration sparking, a semiconducting coating is gradually destroyed, as a result, defects are formed in which partial discharges (PD) appear. In this work, the resistances of semiconducting coatings during thermal aging were investigated. The erosion resistance of the studied coatings in the initial and aged states was compared by the area of defects formed under the influence of vibration sparkling. The minimum geometric dimensions of artificial defects have been experimentally determined, in which slot PDs occur under the conditions of the operating electric field strength. A comparative study of several semiconducting materials currently used in the corona protection system of rotating machines was carried out. Proposed methods for the comparative assessment of erosion resistance, as well as the methodology for assessing operability that takes into account the influence of thermal effects, can be useful in the development of new semiconducting coatings.