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

翻译：功能梯度材料（FGM）被应用于高压直流气体绝缘输电线路（HVDC GIL），以控制直流绝缘系统内的电场。在HVDC GIL中，采用具有电导率空间分布的FGM（电导率-FGM）来控制直流稳态条件下的电场。然而，除直流稳态外，还会出现不同的直流工况，例如直流接通过程、极性反转和雷电冲击。在这些条件下，由于会产生暂态容性电场（其中介电常数对电场起决定性作用），电导率-FGM不足以控制电场。本文建议在绝缘支撑件材料中结合电导率-FGM与介电常数空间分布（介电常数-FGM），以控制直流GIL绝缘支撑件在不同直流工况下的电场，并考虑了绝缘气体和环氧树脂支撑件的非线性材料模型。本文研究了支撑件中介电常数与电导率空间分布的变异对有效电场降低的影响。结果表明，当采用电导率/介电常数-FGM时，电场强度可降低高达65.8%。