You installed a variable frequency drive (VFD). It wasn’t a bad idea. You wanted greater control over production since you don’t need all motors to run at full speed all of the time. It even saves you money on energy and it’s hard to argue against saving money.
Everything seemed to be going well until the problems started. Circuit breakers tripped and fuses blew, and your power factor correction capacitor failed. You can’t ignore it; the problems started after you installed the VFD.
It isn’t a mistake to install a VFD. It serves a useful purpose by aiding in production and allowing you to conserve energy but sometimes solutions create new problems and in this case, the problem is harmonic distortion.
VFDs contain AC to DC voltage convertors which are non-linear loads causing distortion of the current and voltage wave forms. Distorted wave forms are defined as harmonic distortion and contain frequencies which are multiples of the fundamental 60 Hz frequency. When present, harmonic distortion can cause resonance and excessive current resulting in transformer overheating, reduced equipment life, tripped circuit breakers, blown fuses, increased I2R losses, and power factor correction capacitor failure.
VFDs aren’t the only culprits. Other devices containing AC to DC Converters that cause harmonic distortion include Uninterruptible Power Supplies, Electronic Phase Converters, SCRs and Induction Heating Units. Whenever you add a new device to your electrical system, please bear in mind that it may cause new problems and plan accordingly.