Electric Field Grading by Permittivity and Conductivity Graded Materials (ε/σ-FGM) for HVDC Gas Insulated Power Apparatus

The progressive development of HVDC transmission system has urged us to develop a novel technique in supporting the performance of DC power apparatus. Functionally Graded Materials (FGM) are one of the techniques that allows us to control the electric field within the DC insulation system. Our previous work has reported that FGM with spatial conductivity distribution applied to a 320 kV DC-GIS spacer could reduce the maximum electric field under DC steady state condition. This paper investigates the applicability of the combination of spatial permittivity and conductivity graded materials (ε/σ-FGM) in DC power apparatus. ε/σ-FGM are revealed to be more effective in suppressing maximum electric field as well as more uniformly distributed electric field against the increase of temperature distribution under polarity reversal, DC-on, and impulse superimposed on DC condition.