Type HWV externally-mounted vacuum OLTC is a new vacuum tap changer developed by Huaming. It is composed of diverter switch, tap selector, oil tank and motor drive unit. The diverter switch and tap selector of HWV is consolidated in one oil chamber. iT is suitable for power and industrial transformers of Star or Delta connection. Its highest equipment voltage is 40.5 and 72.5kV; its three phases current is less than 1200A and rated frequency is 50 or 60 Hz.