Impact of coatings delamination on the performance of stress grading in form-wound stator coil

This paper investigates the influence of coatings delamination of form-wound motor coil on the effectiveness of stress grading coatings (SGCs). The performance is quantified in terms of imposed electrical stresses due to delamination in several locations. The performance of stress grading coating is analyzed under fast-rise time pulse voltages using a finite element analysis (FEA). Definitely the location of delamination represents a weak point to allow partial discharges that ultimately erode a hole through the insulation. Various locations of delamination are investigated in order to determine the severest conditions affecting the performance of SGC. From the obtained results, the air voids from delamination have an impact on the efficiency of stress grading coating under impulse voltage stress. It was found that, the most critical air voids are those resulting from overlap failure between the SGC and the semiconducting coating.