Recently installed a large VFD (350hp) in an industrial facility. Measured THD after install was 30%. Installed a line reactor and THD dropped to 21%. HID fixtures are flickering, presumed cause is the harmonic distortion caused by the VFD. Considering changing the HID ballast from magnetic to electronic to try to solve the lighting flicker. Does anyone has experience with a similar problem?
Does the flicker correspond to what the motor is doing? i.e. accelerating? I hate to tell you this, but disruption tolerance is often not part of specifications. Some ballasts behave like common lighting devices, but some have a rock steady power regulation like a computer power supply (where sag/dip passthru to output is totally unacceptable). One model of ballast, you could run it on the same branch circuit as an air compressor and you wouldn't even know the compressor started. This is more of an exception. The specification will be such that electronic ballasts will stay within regulation within the bounds of lamp NOT extinguishing, but visible nuisance due to excess dv/dt is not covered.
Asking factory engineer may not help as such conditions are not always tested for each model. You'll find replacement models that supersedes older ones don't always perform the same. So, if I were you, I'd try to borrow/buy several candidate models from your distributor. Make sure the sample is the same model they have available to sell, not the older model that will be superseded.
With that much THD observed at lighting panel, it sounds like VFD and lighting are sharing the 480/277 transformer.
You really should address the harmonics issue though. With 21% THD, other motor loads that share this power will not be happy.
