Dependence of Charge Behavior on Electric Field Distribution around GIS Spacer under HVDC Application and Polarity Reversal

Summary

Under HVDC application, we have to consider the charge behaviour on the GIS solid spacer for accurate numerical computation of DC electric field. In addition, when DC polarity reversal as the operation of the DC power transmission system is done, the accumulated charge may strongly distort the electric field distribution in the transient state. In DC field analysis, the conductivity of every dielectric material in the insulation system becomes important factor as well as its dielectric permittivity. However, the conductivity of gaseous dielectrics is not easily determined. This is because the conduction current would be less dependent of electric field strength in the practical field level when the only natural ionization of gas molecules plays a role as a source of conduction current. In addition, other sources such as electron emission from the cathode electrode may be nonlinearly dependent on the electric field strength. Therefore, the charge behaviour; charge generation, conduction and relaxation in the insulation system should be taken into account for the DC electric field analysis. This paper includes the quantitative analysis of electric field and charge accumulation under HVDC applications and the polarity reversal of applied DC voltage. Especially, we assumed the generation of space charge in insulating gas derived from the electron emission as well as the natural ionization of gas molecules. From the analysis results, we define the “equivalent conductivity” of insulating gas close to the gas/solid boundary in uniform and quasi-uniform field distributions. Consequently, we would propose the best way to choose the volume conductivity of solid dielectrics in order to reduce the enhancement of electric field in transient state.

Additional informations

Authors

Gjonaj Erion, Franck Christian