Stress control system for composite insulators based on ZnO-technology

Stress grading of the flashover distance of hollow insulators and composite tension insulators is necessary to improve the electrical and environmental performance and to reduce material needed. Hollow composite insulators are generally designed in such a way that the outer stress is below the breakdown stress of air. Due to this requirement a large diameter of the insulator is needed. To achieve a slim hollow insulator, which is only designed on required mechanical properties, stress grading of the flashover distance is needed. This stress grading can be achieved by a stress control coating based on ZnO. Design criteria for hollow insulators to improve the impulse withstand behaviour and reduction of the leakage current under environmental conditions are discussed in this paper.