Corona suppression by a semiconductor coating in high voltage insulation systems

Corona is initiated in high-stress regions and thus it can be suppressed by applying a semiconductor coating on the surface to relieve localized high stresses in those regions. Our investigation shows that silicon carbide has an excellent non-linear current field (I-E) characteristic and it is therefore a very good semiconductor-coating material for effective corona suppression. Theoretical analysis and experimental results indicate that for semiconductor materials with constant resistivity the optimal value of the surface resistivity ρ
s
is around 10
⁹
Ω per square for effective corona suppression, while for semiconductor materials with a non-linear I-E characteristic such as SiC, the optimal criterion is that ρ
o
must be higher and the slope dρ
s
/dE smaller at near zero field. Discussion on the choice of ρ
s
-E characteristic for corona suppression for various power apparatus is given.