Capacitor reforming applies to converter modules which have electrolytic DC capacitors in the DC link.

About capacitor reforming

Converter DC link capacitors need to be reformed (re-aged) if the converter has been nonoperational for more than one year.

The function of the capacitor is to act as a power supply filter. It’s comprised of two strips of aluminum foil (called plates) separated by a paper insulator. The foil and paper are rolled into a cylinder and immersed in an electrolyte solution consisting of an ethyl glycol fluid. All of this is placed inside an aluminum can and sealed up via some sort of rubber safety vent plug system.

The capacitor works by storing a DC charge between the two plates. One of the plates has an insulating oxide layer that is created & maintained when the capacitor is charged up. It is this insulating oxide layer (called a dielectric) that is crucial to proper capacitor operation. If the dielectric was not present, the capacitor would short circuit and draw large amounts of current. When large amounts of current flow into the capacitor, it causes the electrolyte solution to boil and turn into a gas. Once turned into a gas, pressure builds rapidly until, hopefully, the safety vent plug releases pressure.

This rupture can be very dramatic and destructive. Not only is the boiling liquid and gas hot, it is also corrosive and will damage any components covered by the solution.

The dielectric oxide-insulating layer is created during manufacture. However, it will deteriorate in the absence of a sufficient rejuvenating voltage, and eventually the capacitor will fail if voltage is not applied. Maintaining the integrity of the dielectric requires the steady application of power. When voltage is applied, the oxide layer is rebuilt. The oxide layer thickness is the crucial factor to determine the voltage rating of the capacitor. Otherwise, the oxide layer will break down under voltage and cause a spectacular failure.

By applying voltage to the capacitor on a regular basis, the oxide layer is “reformed”, and the integrity of the insulating characteristic is ensured.

Without reforming, you run the risk of capacitors getting damaged when the converter starts to operate. It is recommended that you reform the capacitors once a year so that your spare drive is already ready for use when you need it.

Our trained engineers can assess and reform the capacitors as necessary on your drives.