Line Reactor and EMI RFI Filter, does the order matter?

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Cow

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Eastern Oregon
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Electrician
Is anyone putting both of these in front of VFD's? Does it make a difference which one goes first? They would both be right next to the VFD if distance matters.

We regularly use MTE EMI RFI filters in front of all the VFD's on dairies to help with the potential interference with the RFID system for reading the cows ear tags. But after reading more and more posts from Jraef and others on the benefits of line reactors and the little bit of extra insurance they provide to a VFD's longevity, I decided to use them on our current project. I ordered TCI's KDR line reactors, but I'm at the point now that I want to double check the sequence in front of the drive before I bury my underground.

Thanks.
 
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We are looking at fans with VFDs. Tha sales pitch from mfg being filters and line reactors are in the same package or enclosure.

My understanding is Line/Load reactors and all other items should be as close to the VFD as possible. My impression counts for little though.

Enclosures too small?
 

Cow

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Eastern Oregon
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Electrician
We are looking at fans with VFDs. [/B] Tha sales pitch from mfg being filters and line reactors are in the same package or enclosure.

My understanding is Line/Load reactors and all other items should be as close to the VFD as possible. My impression counts for little though. [/QUOTE]

Are the fans for a dairy? Are they being installed in the milking parlor/holding pen area or out in a barn somewhere?


Enclosures too small?


I ordered the filters and enclosures first, then decided to do line reactors. The line reactors are coming in TCI's own UL Type 1 enclosure. TCI's enclosures are pretty well ventilated and I didn't want to take a chance and try to put it all in one box with the filters in case heat became an issue.

I just wasn't sure if the order of the components affected each others ability to function properly.
 

__dan

Senior Member
I will offer a guess, but the place to ask would be the filter manufacturer's engineer.

I would guess line reactor first, upstream towards the supply. The line reactor is just a bar wound on an iron core. For the high frequency transients it will have a tendency to drop voltage instead of passing current. For high frequency components of the load, I am guessing it will have a tendency to rather crudely filter by converting that to heat.

The filter could be a more complexly engineered circuit designed to work with or mate to the drive front end. It would need to see the drive more closely to work as intended. It is possible it is designed to function more elegantly with the drive, but it could also be just a brute force jungle rules device similar to the line reactor.

For high energy destructive transients coming in from the line, the line reactor will be the more indestructible component. Let through that the filter would see would be a lot less.

This guess is for the drive line side as you indicated. Drive load side, the reactor is the typical solution, but adding a load side filter, I would guess the drive manufacturer would have to specify and approve of the device. Very different circuit dynamics.
 

Jraef

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The order doesn't actually matter. The Line reactor is in series with the drive, the EMC filter is in parallel. Generally though, the EMC filters are attached right to the drive (or built in), so the reactor ends up ahead of them both. So your plan is fine, and I agree with your reasoning. Keep the heat from the reactor out of the drive enclosure. It's not really that much, but if it wasn't accounted for in the drive enclosure design, don't risk it.
 

mike_kilroy

Senior Member
Location
United States
Not sure why jraef says filter is in parallel, but agree, either order is fine. Line reactor works on about 30-300 Hz "noise," filter works on about 1,000-5,000,000 Hz "noise." Filter is series inductors too, with added capacitors L-L and L-N, still in series with input.


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Wendo

Member
Location
Wisconsin
Is the problem RFI or is it high frequency noise on the grounding system? I've installed transformers next to drives to prevent the current leakage to ground from going back on the grounding system.

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Cow

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Eastern Oregon
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Electrician
Is the problem RFI or is it high frequency noise on the grounding system? I've installed transformers next to drives to prevent the current leakage to ground from going back on the grounding system.

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They tell me RFI.
 

GoldDigger

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Not sure why jraef says filter is in parallel, but agree, either order is fine. Line reactor works on about 30-300 Hz "noise," filter works on about 1,000-5,000,000 Hz "noise." Filter is series inductors too, with added capacitors L-L and L-N, still in series with input.


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I think that he is saying that some of the elements, notably the capacitors, are in parallel with the VFD output or input.
A line reactor is purely a series element, with nothing but series inductance, AFAIK.
That means that its effectiveness in filtering is purely the result of the motor or VFD input impedance in series with the inductance. It will have its greatest effect at frequencies where those impedances are low, and it may actually have significant parasitic capacitive coupling across the inductor at RF frequencies.
 

Jraef

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Actually, I was jumping the gun a little. I used to be an integrator for a VFD line that had a built-in line reactor on every drive (they went under). That was the first time I ever encountered EMC filter options and for them, the option kit was just the RC network that was wired in parallel, but behind the reactor. I rarely need EMC filters any more, so although I did know that they too are a series device (with a reactor) when sold stand-alone, my mind jumped back about 20 years to my first encounter. Sorry about that.
 
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