Electric-field calculation and grading ring design for 750 kV AC composite insulator

The use of a grading ring is important to improve the E-Field conditions of composite insulators. With FEM, this paper used a static three dimensional model to calculate the potential and E-Field distribution of composite insulator on a cup-tower for 750 kV AC transmission lines. The influence of the configuration and parameters of the grading rings had been analyzed. The configuration of a large and a small grading ring at the conductor side and a medium grading ring at the tower side proved to be reasonable and the insulators in middle phase experienced higher E-Field intensity than that in side phase. The E-Field intensity of insulators and grading rings had been calculated by changing the dimensions and location of the large grading ring and finally appropriate parameters of the large grading ring were recommended. The results of checking calculation had verified that the optimized grading configuration can not only improve the E-Field conditions of the insulator, but also reduce the E-Field intensity of grading rings and end-fittings.