VFD RF noise

[mgcand]

HI Guys
I have installed a Weg CFW09 208v Drive on a 7.5hp 208 volt pump. The motor is 20 feet from the drive. What I got out for results was a disaster , the drive works OK , but I get a lot of RF noise on my ac line that is on the load side of the transformer. Any AM radio on that side of the transformer goes wacky , even a radio in a vehicle that is close by the drive or will be under or over the line wire will go wacky. I had a AB line reactor ( CAT 1321 3R18 B 1.5MH ITH27 ) and installed it on the line side of the drive but didn't get any results ,so I installed it on the load side of the drive and got a 90% of the RF noise cleared up ,want to clear it up 100% . So I am wondering if I could make a line reactor top make some tests on the unit before I go out and buy another line reactor . I would have never noticed a problem if it wasn't for the AM radios.
So if there is somebody out there that could be of any help to me I would appreciate it. If you have any questions let me know.

 

[davidbeach]

You want AM radios to work around PWM drives???? Good luck. You'll probably have better luck at the higher end of the AM band than at the lower end. You won't get 100%, so the 90% you have may be the economical solution.

 

[itsmoked]

Yeah I run a VFD in my living room, it blitzes AM totally. No talk radio...

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[Skogsgurra]

This is what you get with PWM. It is sometimes possible to reduce the RF emission by using filters, shielded cables and good bonding/grounding.

There are many sources of infirmation. Siemens, A-B and ABB have lots of information. Google +PWM +EMC. ABB tells about filters on

http://www.engineeringtalk.com/news/abb/abb118.html

and - of course - there are inverters with a pure sinewave output. They can be used in critical environments and need no filters at all. Micronic (step-and-repeat machines) are using them to keep EMI down in their sub-micron machines.

Gunnar Englund

http://www.gke.org

 

[ozmosis]

Filters will reduce conducted emissions (but not by 100%), meaning that the connected AC supply will have some reduction of RFi travelling back up the mains. However, the other aspect of EMI (Electro-Magnetic Interference) is Radiated emissions and this will be reduced by good installation techniques such as a metal enclosure around the drive, effective bonding techniques to get the RFI to ground and cable segregation methods. Look at the carrier frequency of your WEG drive and try reducing this as much as you can.
However, there is another aspect to EMI and that is immunity. If you are spending lots of $'s on improving the level of emissions, then it could be wated if the offended item's immunity is still below accepted levels. Sometimes you have to improve immunity levels.

 

[mgcand]

It's not that I want to run a AM radio around the drive it's the radios on the line side of the transformer. Some of those radios are 500 feet from the drive.
The transformer is a 600-208v and on the Prim. side there is no noise.
I have talked with some guys that have lost their 485 communication when they installed a drive , and haven't been able to solve their problem.
I am wondering if some drives are morn prone to RFI than others , for I have a CNC with 2 drives and haven't seen a problem.
I was wondering where a person could find some info on making a line reactor for testing purpose ?

 

[Skogsgurra]

mgcand,

Yes, there is a difference. Some drives produce lots of RFI (or EMI, essentially same thing). If your CNC machines are a little older, they may have DC motors and those drives do not emit much RF. Also, a CNC machine is usually installed using the necessary filters and shielding and that means that the problem was taken care of from the beginning. Bonding is also easy in a piece of machinery and the cables are usually short.

Your situation is more or less serious. If you are in Europe, you or your boss may even have to visit jail for some months (yes, true) if you emit too much RF. The EMC directive actually makes that a criminal act. If you are in the US, you have the FCC 15 to care about. Don't know about the jail there.

Find an EMC engineer and have him correct the installation. It is nothing you can do sucessfully yourself. Needs quite a lot of experience and knowledge - and special instrumentation if you need to verify that your levels are OK.

Gunnar Englund

http://www.gke.org

 

[ozmosis]

However, you can check out the basics yourself first. Good bonding is essential as is a good ground.
I have seen many an installation where 1000's of £/$/€ are spent on filtering only to find an effective metal strap in the right place solves the problem.
It is easy to blame the drive but the core of the problem is the path the high frequency interference is taking. You have to understand where that path is and make sure this is 're-routed' down to earth. The only way you are going to do this is by understanding the difference between high frequency and your 60Hz. You need to move away from small round earth cables and fit some flat straps or metal braided straps and try and 'visualise' the path the interference will take. They will take the path of least resistance and small round wire creates a high impedance, especially if it is long.

You use the term "line reactor". I'm not sure what you want to do with this but my interpretation of a line reactor is a simple inductor and this will not mitigate high frequency interference. They are designed for low frequency (harmonics). I don't know how your output reactor improved the EMI effect, it is possible that you may have inadvertantly provided a path to earth through the body of the reactor.

 

[mgcand]

So what it looks like,the smaller and cheaper they make the drives ,, the more they take out so you dont't get the quality as in bigger drives.

Your situation is more or less serious. If you are in Europe, you or your boss may even have to visit jail for some months (yes, true) if you emit too much RF. The EMC directive actually makes that a criminal act. If you are in the US, you have the FCC 15 to care about. Don't know about the jail there.

So if you buy an overseas drive you would get a drive that is low on RF.

 

[jraef]

I'm chiming in late on this, but since nobody else has brought it up yet, how about your wiring method? Many people are not aware that using portable cord or other unshielded cable NOT in bonded metal conduit will turn the cables into a transmitting antenna. Plastic conduit is a no-no and some have told me aluminum is problematic as well (albeit too expensive for the average installation anyway). Not only that, but input, output and control conductors must all be separate. Mixing them can turn one into an antenna even if the problem is addressed in another. How did you wire this up?

If you did use bonded metal conduit, there are EMI/RFI filter kits available for most VFDs that must meet international "EMC" (Electro-Magnetic Conformity) directives, often referred to in the drive mfrs catalog as "EMC Filters" or sometimes "CE Filters". Look in your CFW09 manual under section 3.3 for a description of what to do to meet EMC compliance, and specifically under 3.3.2 for a list of what they call "Epcos filters".

You are undoubtedly male, ergo you did not read the manual. That's not a put-down, I suffer from the same affliction....

Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[mgcand]

Thanks Guys for all info .

I did a test on the drive without the motor hooked up and there was very little noise .
I will be hooking the motor up with a teck so it will have its own wire way, I don't have VFD teck now so I will try it with what I have for now .

 

[Marke]

Hello mgcand

I wonder how you are getting on with your noise problems?

There are some very basic and fundemental things that can be done to reduce the amount of noise that a drive installation produces.

The level of emmission is a function of the drive design/construction and int installation. If you do not have the installation right, adding filters etc will have little or no effect.

First, the drive has has high frequency switching output that gnereates a psuedo sinusoidal current through the motor. The highspeed switching is the source of the energy to drive the motor, and the RFI as well.
One of the first steps is to try to contain the noise within the installation. To do this, you need to run a screened cable between the drive and the motor with the screen clamped at both ends. Do not fall into the trap of separating the screen and separately terminating that via a lug or a flying lead to a point on the chassis. You must use either a copper saddle or a screened gland through the metal body of the drive and motor. If the cable is run through a metal conduit, you wil probably need to bond the conduit to the screen at the entry and exit point of the conduit. One end termination can enhance the noise generated.
The quality of the screening is very important and can make a major difference to the results.
There is special screened cable for drives that includes a very secure screen and a distributed earth conductor within the cable. This can give even better results.
The terminations etc to the cable should be virtually water tight. If you have an isolator between the drive and the motor, mount the isolator in a metal box and bond the cable to the box at the input to and output from the isolator.

Further attenuation can be achieved by passing the output conductors of the drive through a ferrite filter. On small drives, several turns through a single ferrite ring can help.

Once the above is done, an appropriate input filter will also have an effect.

Best regards,

Mark Empson

http://www.lmphotonics.com

 

[mgcand]

Hi guys
I realy apperciate your help on my problem , I havent had time to get to the job site to try your advice , but as soon as I can I will let you know how I made out , it might take a while fore I am busy on a different job.
Again thanks for the help.