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The demand for DC gas-insulated switchgear/gas-insulated transmission line (GIS/GIL) becomes more and more urgent in recent years owing to the rapid development of high voltage direct current (HVDC) transmission systems. Insulators in DC GIS/GIL could easily accumulate a large number of charges on its surface during long-term operation, which might lead to overstressing of polymeric insulation or surface flashover. Therefore, it is of great significance to propose an effective method for dissipating extra surface charges. However, achieving charge dissipation without opening the tank is still a great challenge to SFC6-insulated equipment for a long time. In this paper, a novel method, which is named X-ray based non-contact charge dissipation method (XNCDM) for insulators in SF6-insulated equipment, is proposed. The effects of X-ray irradiation on the charges dissipation and the influences of irradiation dose were experimentally investigated in SF6. The mechanisms underlying are discussed in detail. Results show that surface charges on the insulator can be almost completely dissipated after short-time X-ray irradiation with enough dose, owing to the significant enhancement of electric conduction along the insulator surface and charge neutralization by gas ions near the gas-solid interface. This paper provides a novel technique for realizing rapid surface charge dissipation on the insulator, which is of great significance for a variety of engineering applications of DC GIS/GIL. [ABSTRACT FROM AUTHOR]

Potential substitutes for SF 6 such as fluoroketone (C 6 F 12 O and C 5 F 10 O) and fluoronitrile (C 4 F 7 N and C 3 F 5 N) gases have been widely studied. The electron impact ionization cross section (Q ion) is the key parameter in the simulation of gas discharges. Moreover, the Q ion can be used in the preliminary screening of large scale alternatives of SF 6. In this paper, the Q ion of C 6 F 12 O, C 5 F 10 O, C 4 F 7 N and C 3 F 5 N are calculated via the BEB method. The orbital parameters are obtained by M⊘ller-Plesset perturbation function with second order approximation (MP2), which is validated by comparing the theoretical and experimental Q ion for CH 3 CN, CF 3 CN, C 2 H 4 O, C 3 H 6 O and C 4 H 8 O. The linear relationship between the maximum Q ion and polarisability supports the validity of the BEB method with MP2 function, which suggests that the results of the calculated maximum Q ion for C 5 F 10 O and C 4 F 7 N are reasonable by BEB method. Lastly, the correlation between the maximum Q ion and E r is discussed. The analysis shows that there is a correlation between the maximum Q ion and E r , and the correlation coefficient reaches 0.598. It is thought that Q ion can be as a new predictor to estimate the dielectric strengths for SF 6 replacements. [ABSTRACT FROM AUTHOR]

Detection of decomposition products is a widely studied method for condition diagnosis of SF6 insulated equipment because of its anti-electromagnetic interference and high sensitivity. A 90 L discharge chamber with adjustable defect was designed to simulate typical failures including metal protrusion defect, floating potential defect and insulator defect. Primary products of both the former two defects are SOF2, SO2F2, CO2, and SO2. Concentration ratios including Φ(SOF2+SO2F2+SO2)Φ(CO2) and Φ(SOF2+SO2)/Φ(SO2F2) could be used to distinguish these two defects which have different structures and discharge energy. Influence of essential conditions such as applied voltage, pressure, and moisture content has been investigated under metal protrusion defect. For the insulator defect, several extra carbon containing by-products, namely, CF4, CO, and CS2, are found to be critical characteristic decomposition products. Moreover, a triangle method utilizing composition of decomposition products is proposed. It is proved to be a graphical method which helps to follow the faults more easily and more precisely. [ABSTRACT FROM AUTHOR]

Detection of decomposition products is a newly-emerging method for the condition diagnosis of SF6-insulated equipment. Based on the two grading structures that are commonly adopted in SF6-insulated current transformers (CT), three models consisting of the needle-to-plane, the ball-to-plane, and the plane-to-plane were established. Gas decomposition was investigated in a 90 L discharge chamber under operating conditions. Products were analyzed with gas chromatography (GC) and X-ray photoelectron spectroscopy (XPS). Typical gas decomposition products are CF4, SO2F2, CS2, SO2, and S2OF10. For the needle-to-plane with a gap of 30 mm, near-linear growths with time are observed in the concentrations of SO2F2, SO2, and S2OF10 when the applied voltage is set as 33 kV. Addition of the adsorbent suppresses the concentrations of all three products, especially SO2. Besides, CF4 and CS2 are also found to be the characteristic components of partial discharge involving polyester films. And their concentrations are higher when the electric field lines are parallel to the surface of the polyester. As for the polyester films, the atomic ratio of C decreases, the atomic ratio of S increases, and the atomic ratio of F increases significantly as the deterioration becomes more serious. Moreover, the concentration ratio of S2OF10/SO2F2 in the needle-to-plane is mostly within the range of 0- 2, whether with the addition of adsorbent or not. And the ratio is much higher (2-10) when polyester is involved in the discharge process. It could be used to diagnose the insulation condition of CT effectively. [ABSTRACT FROM AUTHOR]