How do Open Delta Systems affect VFDs and harmonic filters?

Open delta systems may cause some Variable Frequency Drives (VFDs) to trip because of voltage unbalances that may occur. Open delta systems can cause the diode bridge in the VFD to produce higher harmonics and increase DC bus ripple. Higher DC bus ripple can reduce the life of diodes and DC bus capacitors.

On most open delta installations the VFD must be derated to prevent it from overheating. Some utilities may require a harmonic study to be performed when a large VFD is to be supplied by an open delta system.

A passive harmonic filter will help reduce the extra harmonic currents generated by the VFD but it may not meet IEEE 519 guidelines.

Active Harmonic Filters (AHF) may not run on an open delta system. You should consult the AHF factory for guidance when trying to install an AHF on an open delta system.