DC/AC Electric Field Relaxation With Multidimensional Functionally Graded Materials (ε/-σ-MFGM) for Offshore Bipolar HVDC GIS Spacer

This study discusses the application of the multidimensional functionally graded materials (
$\varepsilon $
-/
$\sigma $
-MFGM) for epoxy spacers in offshore bipolar high-voltage direct current (HVDC) gas-insulated switchgears (GIS), which may be exposed to the dc–ac mixed voltage. Based on a cone-type spacer model, the conductivity distribution of the surface functionally graded material (
$\sigma $
-SFGM) and the permittivity distribution of the bulk functionally graded material (
$\varepsilon $
-FGM) are optimized to coordinately regulate the dc and ac electric filed distributions. Simulation and experimental results show that the
$\sigma $
-SFGM spacer and the
$\varepsilon $
-FGM spacer can relax the electric field concentration under a single condition of dc or ac voltage. Compared with the uniform spacer, the electric field strength of the
$\varepsilon $
-/
$\sigma $
-MFGM spacer decreases by 83.4% and 18.5% under dc and ac voltages. Accordingly, the dc and ac flashover voltages of the
$\varepsilon $
-/
$\sigma $
-MFGM spacer increase by about 34% and 15%, respectively.