How useful are EMC fans and outlet filters for reducing EMC/EMI from VFD enclosures?

[designvfds]

I am deciding on components for a bayed modular enclosure containing multiple VFDs (480V/350A/321Hp each) for a dynamometer. I am concerned given the high voltages and currents that EMI/EMC is going to be an issue for components and instruments outside the enclosure.

How useful are EMC fans and outlet filters for reducing EMC/EMI?

I am taking other steps such as shielded cables to the motors to try to reduce the EMC/EMI. My understanding is that wherever there is a cutout in the sheet metal of the enclosure you compromise the shielding. How much improvement does adding EMC fans and outlet filters help to retain the shielding? They are quite a bit more expensive than the non-EMC option.

 

[Gr8blu]

You did not mention whether each drive was intended to power/control a separate machine - or if their outputs would be combined to produce something at 480 V but much higher current than an individual (350A) drive might handle. If it is the second case, consider connecting the external world to the cabinet components via bus, rather than a series of individual cables. Minimizes the amount of "holes' in the casing thereby minimizing the possibility of electromagnetic "leaks".

First - understand the source of both the electromagnetic interference (EMI) and how much of it the components can tolerate (electromagnetic compatibility, or EMC). Anything that carries current w(or is intrinsically magnetic, like magnetized steel) will generate a magnetic field both internal to the device and external. The more ferrous material there is surrounding the device, the better the shielding will be - and the less "interference" is present for nearby devices. Fans used in cooling for power electronics are notorious for using minimal material in the magnetic circuit (trying to keep weight and cost down) - which results in little to no damping for magnetics. EMC-quality fans are better, because they have more material - but in themselves aren't the whole answer. Orientation of the fan is important too - try to keep the magnetic (motor) end away from the electronics and in a different (parallel) plane. This means that if your board is oriented vertically, the outside of the fan casing should also be vertical with the "fan" side facing the board. EMI is different; magnetics can affect signal clarity but so can harmonics created by the switching action of the various drives. Unless you have very good input filters for each drive, your output will get ugly fairly quickly (the old "garbage in - garbage out" philosophy).

And yes - a "hole" in the wall of the cabinet housing the drives will create a "hole" in the electromagnetic shield.

Converting energy to motion for more than half a century

 

[EdStainless]

We used such fans and filters. The biggest factor is that ours were all steel.
Gr8blu is correct about the orientation.
We always pointed such holes either toward the back wall or in a place where we could add baffling.


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P.E. Metallurgy, consulting work welcomed