A.25m B.15m C.10m D.5m
A.1.0~2.2cm/kV B.2.0~2.5cm/kV C.2.6~3.2cm/kV D.>3.8cm/kV
A.1.3cm/kV B.1.5cm/kV C.1.6cm/kV D.1.8cm/kV