How long has your VFD been sitting in storage? When an AC drive remains unpowered for an extended period, the electrolytic capacitors in its DC bus can deteriorate. Before a stored drive is returned to service, capacitor reforming can help reduce the risk of damage caused by suddenly applying full line voltage.
Why VFD Capacitors May Need Reforming
DC bus electrolytic capacitors rely on an aluminum oxide dielectric layer. When the drive remains unpowered for a long period, that dielectric layer can deteriorate. Applying full voltage to a degraded capacitor can produce excessive leakage current, overheating and potentially serious capacitor or drive failure.
Many drive manufacturers provide long-term storage procedures and may call for capacitor reforming after extended periods without power. Always follow the procedure and storage interval specified for the particular drive manufacturer and model.
What Is Capacitor Reforming?
Capacitor reforming is a controlled process that gradually applies voltage while limiting current so the capacitor’s internal oxide dielectric layer can rebuild before the drive is subjected to normal operating voltage and load.
A properly controlled voltage ramp allows the capacitor’s electrochemical self-healing process to restore the dielectric layer while reducing the risk of excessive current and thermal stress.
Why Simply Applying Full Power Can Be Risky
A VFD that appears new may still have spent a year or more sitting on a shelf or in a storeroom. If its DC bus capacitors have degraded during that time, immediately energizing the drive at full line voltage can place significant stress on them. Proper evaluation and reforming before startup can help protect the drive and avoid an unexpected failure during commissioning.
IPS Folcroft Capacitor Reforming Service
IPS Folcroft can provide capacitor reforming for low-voltage VFDs that have been in long-term storage or otherwise require evaluation before being returned to service. Our industrial electronics team can help determine an appropriate approach based on the drive manufacturer, model, age and storage history.
If the drive also requires troubleshooting or repair, visit our Industrial Electronics Repair Services. For onsite startup, commissioning and troubleshooting support, see our VFD Field Service, Startup & Commissioning capabilities. If replacement is the better option, browse current inventory in the IPS VFD Store.
Have a VFD That Has Been Sitting in Storage?
Contact IPS Folcroft before energizing a questionable stored drive. Provide the manufacturer, complete model number and approximate length of time the unit has been unpowered so our team can review the application and discuss capacitor reforming service.