Mitigation of field stress with metal inserts for cone type spacer in a gas insulated busduct under delamination

Abstract

Increased power demand and energy density in cities resulted in the establishment of Gas insulated systems (GIS) as a substitute for the conventional air-insulated substations. Reliable and efficient design of the modules in GIS has been a major concern for the power engineers. Major dielectric strength breakdown and surface flashover causes were reported due to insulator failures like excessive field enhancements at the triple point junction formed by the electrode-gas-insulator interface. The insight of reducing the field along the surface of the spacer exhaustive field study was carried out on a conical spacer. Initially, a field study was carried out with a normal type spacer then extended to a molded spacer done with various shapes to obtain an optimal field spread. This Shape control may sometimes lead to very uneven shapes. Further, a functional graded material (FGM) is designed for the standard cone type spacer to obtain uniform field stress along the surface of a spacer to overcome the above problem. The grading of the spacer is done with different permittivities. Electric field is computed for different cases of graded spacers and Tuned Metal inserts and recessed electrodes were also imbibed in the spacer geometry for a better field distribution. The work was validated by comparing the optimal mold spacer field distribution with that of the FGM cone type spacer. Inspite of proper care taken during the manufacture, working, and maintenance of the spacers several flaws do occur. The delamination effect is considered and similar analysis is carried out and the results are presented and analyzed. Keywords: Gas insulated busduct, Insulation, Insulator, Electric field