Potential calculation and grading ring design for ceramic insulators in 1000 kV UHV substations

The electromagnetic environment of insulators in substations is more complicated than that in transmission lines, this difference gets more prominent as the system voltage increases. Considering all the influencing factors, this paper presents the calculation results of the potential and electric field distribution of the ceramic insulator strings in 1000 kV ultra-high voltage (UHV) substations, using a three-dimensional (3-D) finiteelement method (FEM) software. Factors that affect the potential distribution such as grading ring, jumper, string structure, mounting location and drop conductors have been analyzed. The structural parameters of grading ring were optimized. A use of double ring was proposed for terminal tension insulators. A true-type test was carried out to verify the reliability of the FEM calculation method and results. The optimized grading ring configuration was successfully applied on the 1000 kV UHV pilot project in China and it was proved very effective by field observations with an ultraviolet camera.