VFD EMI Filters Used in Conjunction with Line Reactors

[Cfarek]

Does placing a Line reactor ahead of a drives built in EMI filter make it ineffective? Allen Bradley claims the caps on the EMI filter are so small they will have no affect on the Line reactor and MTE claims by adding more inductance and capacitance you unbalance the EMI filter. Has anyone ever done something like this? What are your thoughts?

 

[Jraef]

Does placing a Line reactor ahead of a drives built in EMI filter make it ineffective? Allen Bradley claims the caps on the EMI filter are so small they will have no affect on the Line reactor and MTE claims by adding more inductance and capacitance you unbalance the EMI filter. Has anyone ever done something like this? What are your thoughts?

Do you realize that both statements can be true? The AB statement is from the perspective of the EMI filter's effect on the REACTOR, the MTE perspective is on the effect on the FILTER.

But MTE's claim has a hole in it: a line reactor does not add capacitance, only inductance. They might be thinking of a Passive Harmonic Filter, not just a plain old line reactor. A PHF is a reactor plus an RC filter tuned to the 5th, and maybe the 7th harmonics. Adding the caps that are in an EMI filter can set up a resonance with that RC network.

While it's true that there is a theoretical possibility for the added inductance of the reactor causing a different kind of resonance to be created in the EMI filter caps that might have an effect on meeting EMC requirements, that risk actually exists in the transformer feeding the drive too, and is so low that nobody bothers worrying about it.

 

[Jraef]

There is another possibility for their comment, I just found it. IF the drive is "regenerative", as many DC drives are and some AC drives now, the EMI filter must be placed ABOVE (up stream) of the reactor, because if the EMC filter is installed between the line reactor and the drive, slight input current oscillations that may occur might prevent the drive from synchronizing to the line for regen.

 

[Rho_HV]

Does placing a Line reactor ahead of a drives built in EMI filter make it ineffective? Allen Bradley claims the caps on the EMI filter are so small they will have no affect on the Line reactor and MTE claims by adding more inductance and capacitance you unbalance the EMI filter. Has anyone ever done something like this? What are your thoughts?

Line reactor has no capacitance; what is MTE talking about?:blink: