VFD--Double-Stage High-Efficiency Vacuum Insulation Oil Purifier Application VFD series is mainly used to improve the properties of insulation oil. It can remove trace water, gas, particulate matters etc. from the insulating oil effectively and rapidly so as to boost performance of transformers, circuit breakers, mutual inductors, cable and capacitors which has insulation system. VFD series specialize in purifying branded oil, insulating oil of high voltage and super high voltage transformer. Additionally, it is suitable for treating low viscosity lubrication oil.