Dielectric performance of insulator surfaces in clean air for high voltage gas insulated switchgear application

Summary

This paper summarizes the results of an extensive study on the dielectric performance of clean insulator surfaces in Clean Air environment. The influence of several parameters like gas pressure and gas moisture, size of surface area and voltage wave shape were investigated. The tests were performed with a cylindrical insulator model arrangement representative for typical insulators of gas-insulated systems in terms of material type, manufacturing technology and size of electrical high stressed surface area. The test samples were made of alumina-filled cast resin material with embedded alumina electrodes. The design of the model arrangement was chosen to concentrate high electric field strength on the insulator surface, avoiding high electric field stress at triple junction. The tests were performed with AC voltage and lightning impulse voltage of positive and negative polarity. To achieve resilient test results, a high number of tests was performed and the test results were evaluated by statistical methods, considering e.g. effects of previous flashovers on subsequent flashovers. The test results support the safe and reliable dimensioning of different types of epoxy insulators for gas insulated switchgear with Clean Air as insulating gas. 1 INTRODUCTION SF6 is used in high voltage equipment for insulating and arc quenching purposes since mid of last century. Many attempts to replace SF6 were started in the last decades (summary is given e.g. in [1]) because of its high global warming potential (GWP). Clean Air - consisting of 79.5% nitrogen and 20.5% oxygen - is considered as suitable alternative to SF6 as insulating gas. The insulation properties of Clean Air are not on the same level as for SF6 of the same pressure, but its application gives major advantages concerning ecological aspects (GWP=0) and e.g. easy and riskless gas handling, chemical stability and low chemical interaction with other materials. The long-term stability of dry air is well proven e.g. by earlier gasinsulated switchgear technology based on air blast circuit breakers

Additional informations

Authors

CAMPOS, Batista Suelson, SANTIAGO, MH FERNANDES

Keywords

Clean Air, GIS, alternative gas, insulation