Discharge and Gas Decomposition of Typical Insulation Defects in 500 kV SF₆ Current Transformer

Two 500 kV SF₆ CTs with aluminum cylinder grading structure and cone capacitor grading structure are selected to analyze discharge and gas decomposition characteristics of insulator surface defect and combining defect. The influences of defect type, discharge path length and sampling positions are discussed. It is found that measuring PRPD is an effective assistant method for gas analysis. The detection results of the improved sample port are more accurate than that of regular one. Typical gas decomposition products of the insulation material related defects are CF₄ and CS₂. In insulator surface defect, concentration of SO₂ is higher than SO₂F₂; the growth rate of S₂OF₁₀ concentration is relatively low; types of decomposition products vary with discharge path length. In the combining defect, the growth rates of SO₂F₂ and SO₂ are relatively higher than that of S₂OF₁₀.