VFD EMI mitigation

kallileo

Lifetime Supporting Member
Join Date
Jun 2008
Location
Thessaloniki, Macedonia, Hellas
Posts
353
I have come across an installation on a farm where a Delta 3.7KW ac drive is controlling three 1.1KW ventilation fans. So they asked me for help because when all the fans are on the RFID detection system on the calf feeding machine stops detecting the calves entering the feeding box. :ROFLMAO:

The motor cables are shielded and grounded both at the motors as well the drive sides but they are really really long. The cables are 30, 40 and 70 meters long for the 3 motors so the overall length is around 140-150 meters.
I'm not sure how well the grounding of the cable shield was performed.

The first suggestion I see in Delta manual is to put a line reactor on the input in order to reduce harmonics and I think they definitely need to put reactors on the outputs to the motors as well. The last solution that I would like to avoid is to install a transformer just for the supply of the ac drive.

What do you think?
 
Line & load reactors sound like a good place to start. You could also take a look at the carrier frequency. I think that a lower frequency would be better, at least from the standpoint of the long cable runs. It might also help with your interference problem.
 
I will watch this thread closely. I have done a lot of research on this question and I have never come up with any concrete answers yet. I look forward to more input!
 
Care must be taken with the installation of VFDs in a dairy facility. The interruption of the RFID system is a nuisance but this level of harmonics has a potential to majorly affect the production and health of the animals.
I have been involved with extensive field testing in the past on how to minimize this. Reactors, etc may revive your RFID system, but the best method is to install a VFD as close as possible to each motor. Yes it's a pain to install and service, but the payoff for the farmer is more important.
Always use a good qualilty VFD cable and properly connect the grounds.
 
EMI could be radiating from the INPUT connections. Seeing that you are in Greece, hopefully your VFDs are of the type that has the built-in EMI line side filters. If not, the first thing I would do is to add them.

Looking at some Delta drive literature that I have on hand, it appears as though they do NOT include the EMI filters in their drives, they are an accessory that you must add. So if you don't have that accessory, you were supposed to have installed them all along in order to meet EU directives. The installation manual should have a list of the appropriate EMI filters for your model.
 
The motor cables are shielded and grounded both at the motors as well the drive sides but they are really really long. The cables are 30, 40 and 70 meters long for the 3 motors so the overall length is around 140-150 meters.
I'm not sure how well the grounding of the cable shield was performed.


I thought the shield was only supposed to be grounded one end, to prevent earth loops? Or are you taling about the internal cable earth?
 
I thought the shield was only supposed to be grounded one end, to prevent earth loops? Or are you taling about the internal cable earth?

My first thought also....shields grounded at output side, not the end device.
 
Ground loops are a concern for analog signals.
Ground loops are irrelevant for motor cables. You can and should connect the screen at both ends on cables to motors that are driven by a VFD.
 
The inverter has built-in EMC filter but obviously it's not enough.

https://uk.rs-online.com/web/p/inverter-drives/8603919/

Excerpts from user manual:

If a filter is required for reducing EMI (Electro Magnetic Interference), install it as close as possible to AC drive. EMI can also be reduced by lowering the Carrier Frequency.

From the table, we see that the PWM carrier frequency has a significant influence on the
electromagnetic noise, AC motor drive heat dissipation, and motor acoustic noise.


http://www.realimpeks.co.rs/download/delta_vfd_el.pdf

The first thing I'am going to try is to lower the carrier frequency and see what happens.

It seems that the guy in the video below has exactly the same problem and it is present in all farm that I have visited. There is another farm where the farmer has to stop the fans during milking so cow identification system can work.
https://www.youtube.com/watch?v=IwQ-lo1obbA
 
The majority of our everyday work is wiring large dairies.

Standard procedure for us, is the VFD is located as close as possible, EMI/RFI filters, Line Reactors, and shielded VFD cable to the motor.

We have not had any RFID issues doing it this way.
 
@kallileo

I was curious if you were able to implement any of the changes yet and what/if made any difference. I have an application coming in that I will want to take care on this point.
 
Other things to consider:


- Earthing of cable-ways/conduit that the motor cables are run in.

- Earthing of cable-ways/conduit that the RFID supply/comms are run in.

- Segregation of motor cables from supply and comms to RFID systems.

- Check the earthing on the motors and panels themselves.
 

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