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PF for Across line and VFD motors


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I have a mill that has a several motor control centers each with a mix of full voltage across line starters, vfd's and soft starts. The larger motors 200 to 300hp have soft starts with electronic braking. I want to install bulk correction using automatic pfc banks at the main switchboard. Is there a potential for causing problems with the vfd's and soft starts and if so, how could I prevent this?
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Hello pmeredeth


Welcome to the forum.


Bulk correction will not normally cause problems in this situation. It is commonly applied, however I would strongly recommend that you install detuning reactors with the capacitors in order to reduce the harmonic current flow through the capacitors (causing heat and reducing the capacitor life) and also to reduce the supply transients as the capacitors are switched in and out of circuit.


For bulk correction, you need to use a controller to automatically switch the banks in and out of circuit as the load changes.


One note of caution, if the supply impedance is reasonably hgh or inductive, you can have supply resonance problems causing very high voltages on the supply. This can in turn result in damage to the SCRs used in soft starters. I would recommend using line contactors with the soft starters to minimise and damage.


Best regards,

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