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Wait More Than a Year, Fuses You May Clear

April 17, 2017

Virtually all low voltage Variable Frequency Drives (VFDs) that have not been powered up for over a year must be reformed or they could vent upon power up causing serious damage to the internal components of the Drive. Quad Plus offers reforming services both onsite and in house, as well as Capacitor bank studies and evaluations.

SIEMENS OEM states: “If a unit has been non-operational for more than one year, the DC link capacitors have to be newly formed. If this is not carried out, the unit can be damaged when the line voltage is powered up.

If the unit was started-up within one year after having been manufactured, the DC link capacitors do not have to be re-formed.”

Most low voltage VFD’s use internal Electrolytic Capacitor banks for energy storage to be modulated to the motor. Over time while not being used their internal dielectric Oxide layer can become less consistent in thickness throughout the capacitor. This causes current to flow unevenly throughout the capacitor and may lead to dielectric failure under static voltage.  This inconsistency causes heat buildup within the capacitor which can lead to internal over-heating, leaking and inevitably venting the capacitor or capacitors. Reforming involves gradually increasing the Bus Voltage and monitoring the current to reestablish an even dielectric layer, thus evenly distributing current flow and heat to within the Capacitor manufacturer’s design specifications.