Can variable frequency drives be powered from an open delta system?

There are several issues that occur when a Variable Frequency Drive (VFD) is powered from an open delta system:

  • Uneven voltages in an open delta circuit can cause the diode bridge to unevenly draw current which causes additional heating.
  • The current harmonic distortion caused by the diode bridge will also not be balanced line to line which will cause even more additional heating.
  • Some utilities may require a harmonic study to be performed anytime a large VFD load is to be supplied by an open delta system.

Overall, an open delta system can result in shorted diodes or DC bus capacitor failures on a VFD. Using DC Link Chokes and/or Line Reactors will mitigate some of this additional distortion. The VFD may need to be de-rated for open-delta configurations.