VFD EMI filters 2

[itsmoked]

Have a Baldor ID15201-E 1hp drive.

It's provided 1ph, 60Hz, 240V input.
Driving a 1725 1/2hp 3ph, 240V motor.
The drive is wired 15 feet to the panel.
The motor is 4 feet from the drive.

It's been working flawlessly since 93. Recently the EMI it puts out has become annoying so I need to muzzle this thing a bit.

Can someone point me to the proper, or at least typical, AC reactor or filter I should use with a VFD? Baldor's site is coming up with nada.

Is this the type device I need or are VFD filters somehow different? (note: link takes a few seconds)

http://www.alliedelec.com/catalog/pf.asp?FN=789.pdf

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[ozmosis]

Keith
If the problem is EMI then an AC line reactor will not help. You need a specific RFI filter.
We use Schaffner when we don't make our own. A FN350 might suffice. In the USA they are:

http://www.schaffner.com/components/en/product/productL23.asp?level=2$1$3&language_id=12

 

[Marke]

Hi Keith

The first step in defeating the EMI problem, is to ensure that there is a very good earth path between the motor and the inverter. This must be a direct path, not via another earth.

The best means of connection, is by using an EMC rated screened cable between the inverter and the motor with the screen earthed at both ends. - many "experts" will tell you to earth one end only, but between the VFD and the motor, you must earth both ends, preferably with a screened gland or a clamp. If you do not have this right, then no level of filtering on the input will get you optimum results.
I have solved many EMC problems just by correcting the cabling between the inverter and the motor. Ferrite rings on the output cable (not including the screen) will help to reduce the rate of rise of current and will reduce the noise generated.

When the output connections and ferrites have been fitted, then if there is still a problem, add a proper EMC filter to the input. In many cases, the EMC filters are matched to the drive input characteristics for maximum performance.

These three steps will usually solve most problems.

Best regards and good luck,

Mark Empson

http://www.lmphotonics.com

 

[ozmosis]

Well put Mark. I got lazy and just responded to Keith's direct request rather than outlining the potential 'real' problem.

 

[itsmoked]

Thanks to the both of you.

Currently the four feet of wire to the drive is SO cord. 4-14. It is carrying a ground that is screwed to the motor casing and to the aluminum drive housing directly under the ground line from the service panel feeding the drive.

Is that grounding, Marke, what are you suggesting in your first line?

I recognize the shielding problem. That is of course a bigger hassle to change but I will be changing it if other solutions don't solve this. Where does one look for shielded drive cable? Is there a standard name for it for light duty, like 'SO'???

If I try a ferrite ring, all three conductors need to run thru the ring at the same time right?

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[dpc]

Keith,

For drive to motor cable, Okonite C-L-X metal-clad cable works well. Maybe you can ask for a four foot "sample"

Ferrite bead needs to go around all conductors. Basically a choke for high-frequency common-mode current. At least that's how I've always used them.

 

[itsmoked]

Got it dpc!

That's what I was expecting the common-mode.

Thanks!

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[Marke]

Hi Keith

Yes, here, in Kiwi speak, we refer to earthing where you refer to grounding. It is the same, just we do it before you (earlier time zone) and on the other side of the globe!!

The critical thing in the earthing (grounding) is that the high frequency impedance must be very low. The screening is a separate issue which adds further attenuation.
From the perspective of the HF noise, the inverter is the source of this noise and you need to provide a very low impedance return path to the source, otherwise the noise will crawl out through all the other grounding paths finding its way home and the larger the loop, the greater the radiation!!
The best cables have a very tightly woven copper braid around the main conductors, and a set of balanced earth conductors as well such that there are three earth (ground) conductors evenly distributed within the cable so that you go phase ground phase ground phase ground as you go around the cable. You bond the screen with a screened gland or a clamp to the body at both ends and run the earth (ground) to the terminal at both ends.
Lesser screened cables will give lesser results. I have seen tables showing the effective attenuation on an installation for different types of cable and it can be many db.

The ferrite rings go around the three output phase conductors only for common mode rejection. More rings, better attenuation. This helps to reduce the noise actually generated which make it easier to filter.

Another thing to look for, if you are feeling adventurous, is to ensure that there is a decoupling capacitor from the DC bus to ground. Most modern drives now have this, but I still come across drives that do not decouple the DC bus. In many drives, the positive side of the DC bus is brought out for the connection of a brake resistor. Connect a decoupling capacitor from that terminal to ground and you may find an appreciable improvement. Be careful though, this is HV DC.

Best regards,

Mark Empson

http://www.lmphotonics.com

 

[itsmoked]

Thanks again Mark!

I shall endeavour to persevere.

I'll return with results eventually.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[dpc]

Here's the C-L-X datasheet if you're not familiar with it. There should be a stocking sales office in your area.

http://www.okonite.com/Product_Catalog/section3/sheet9.html

 

[itsmoked]

Thanks dpc.
Now to find a measly few feet...

I take it flex is pointless because the spiral essentially means you're trying to run the high freqs down a coil.

What about the metal filled liquid-tite, or is it identical to flex just with a plastic jacket?

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[sreid]

Belden Motor Cables

http://bwccat.belden.com/ecat/jsp/I...efined&P4=undefined&P5=undefined&P6=undefined

 

[dpc]

The liquid-tight would be an improvement, but the C-L-X sheath is a continuous extrusion. Also, the C-L-X comes with three ground wires which is supposed to help with EMI reduction.

There are some other options also for shielded cables such as Mark mentioned. You might try local electrical distributor and see what they have in the way of "VFD cable".

Just putting it in some rigid conduit would help a lot - but you'll need some kind of flexible connection at the motor.

 

[ozmosis]

I would recommend Belden as well.

 

[macmckim]

If your in USA - company in Milwaukee mfg RFI/EMI filters.
web site:

http://www.mtecorp.com/rfiemi.html

Have use this product in the past and seem to work quite well to attenuate RFI interferences