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Functionally graded materials (FGM) are applied in HVDC gas insulated lines(GIL) to control the electric field within the DC insulation system. In HVDCGIL, FGM with a spatial distribution of the electric conductivity(conductivity-FGM) is applied to control the electric field under DC steadystate condition. However, besides DC steady state, different DC conditionsoccur, e.g. DC-on process, polarity reversal and lightning impulse. Under theseconditions conductivity-FGM is not sufficient to control the electric field,since these conditions result in transient capacitive fields, where thepermittivity is decisive for the electric field. In this paper, we suggestcombining conductivity-FGM and a spatial distribution of permittivity(permittivity-FGM) in the spacer material to control the electric field aroundDC-GIL spacer for various DC-conditions, considering nonlinear material modelsfor the insulating gas and the epoxy spacer. A variation of the spatialdistribution of permittivity and conductivity in the spacer is investigated inthis paper for an effective field reduction. The results show a reduction ofthe electric field intensity up to 65.8 %, when conductivity/permittivity-FGMis applied.

Simulation of Permittivity and Conductivity Graded Materials for HVDC GIL for Different Voltage Forms