Ethernet comm problem with PLC when inverter enables.

[AB2005]

Hi;

In a cabinet of a machine, a Fatek PLC with an Ethernet communication card is working. In the same cabinet, there is a 1 kW inverter. When the inverter is enabled, PLC communication creates problem. Kindly guide me on how to eliminate the issue.
The Ethernet cable is far from the inverter power and motor cables. When inverter is disabled, no problem with communication.

 

[JesperMP]

Check screen in cable from inverter to motor.
Check screen of ethernet cable.
Check grounding.
If the motor cable is very long, it may be necessary with an output filter on the VFD.

 

[goghie]

What measures did you already implemented in order to avoid VFD induced disturbances?

 

[AlfredoQuintero]

I would advice to also check the category of your Ethernet cable. If you are using category 6, maybe go for better quality, such as category 7 which is shielded.

 

[joseph_e2]

New install or existing system?
If existing and it's been ok for a while, check for:

• loose connections, especially of shields/drains/grounds.
• damaged cabling (shielding of VFD/network cables for example).
• damaged/open/etc. enclosures or loose conduit fittings

 

[goghie]

@AlfredoQuintero , to be more precise - every category from cat5 until ca7 has options of unshielded and shielded cables.
Here is good explanation:

Universal Networks

www.universalnetworks.co.uk

I would select at least S/FTP cable cat6, but that could be not enough.
OP should give more info...

 

[AB2005]

Hi

Thanks for answers.
It's new installation.
I have checked that there is almost 2.5V in between neutral and earth.
PLC RS232 comm is ok. Problem is just with ethernet. Ethernet is using just for programing i.e from PLC to Laptop.
The cable is cat5.
For motor cable, I need to verify if screen is connected at both ends.

 

[jstolaruk]

A common problem when non-VFD cable is used to wire a motor to a VFD - usually someone is trying to save the cost without understanding the down-side.

 

[lfe]

If the motor cable with VFD is not shielded and runs next to other cables, the noise spreads throughout a large part of the installation.

It must be shielded or run in a separate path from any other cable, ideally inside a metal conduit.

It is also important that there are no floating electrical supplies not connected to ground.

 

[goghie]

@AB2005 you should give us full picture, so we can help you.

For now we know that it is Fatek PLC with Ethernet and RS232 coms, with VFD of unknown brand and there are unknown measurements done in order to mitigate noise (seams like nothing is done in order to prevent it).

For example is it TN-C, TN-S, TN-C/S, TT or IT?
Are there any kind of filters installed?
Are there PFC banks installed?
Have you done any kind of measurements?
To what is that RS232 connected?
etc...

 

[bill4807]

It is also important that there are no floating electrical supplies not connected to ground.

Yes, definitly check this. As well as control transformers with floating neutrals.

 

[AB2005]

@AB2005 you should give us full picture, so we can help you.

For now we know that it is Fatek PLC with Ethernet and RS232 coms, with VFD of unknown brand and there are unknown measurements done in order to mitigate noise (seams like nothing is done in order to prevent it).

For example is it TN-C, TN-S, TN-C/S, TT or IT?
Are there any kind of filters installed?
Are there PFC banks installed?
Have you done any kind of measurements?
To what is that RS232 connected?
etc...

For example is it TN-C, TN-S, TN-C/S, TT or IT? I need to verify as I am just working at a machine of a customer.

Are there any kind of filters installed? No.

Are there PFC banks installed? Yes. Setpoint of PF is 0.95.

Have you done any kind of measurements? I just increased the size of earth cable. Others measures would be done today or tomorrow.

To what is that RS232 connected? HMI.

etc...

I have temporarily installed an Ethernet switch to connect the HMI and PLC simultaneously with the PC. Since the PLC has two communication modes, RS232 and Ethernet, the RS232 is dedicated for PLC to HMI communication. However, when the inverter enables and the motor runs, there are fluctuations in the communication between the laptop, PLC, and HMI.

The old (PCB type) outdated controller in the machine is being replaced with a Fatek PLC. I have installed the PLC, relays, and power supply, while keeping the original wiring intact.

 

[goghie]

Ok.
I hope that VFD is not 1x230V input with 3x230V output. It will make your life much harder.
Just to mention that every advice you got in previous posts was correct, so I'm just adding additional measures.
This is oversimplified suggestion/answer:
1. Take S/FTP cable, that is long enough, so you can avoid passing near power cables. If you need to pass near power cables, try to do it with 90 degrees.
2. Be sure that every GND on PLC and its modules is directly referenced to ground. Avoid loops.
3. Be sure that HMI GND is directly referenced to ground.
4. Be sure that VFD GND is directly referenced to ground.
5. Be sure that all shielded signal cables have shield connected to GND, but on only one side.
6. If grounding system is TN-C, than make it TN-C/S in you enclosure, by converting PEN to PE and N. Earth connector should be at least same size as supply cable.
7. Check motor grounding.
8. Add isolating transformer for control line 400/230V.
9. Make sure that Fault Ground and Logical Ground are different wires.

 

[AB2005]

Ok.
I hope that VFD is not 1x230V input with 3x230V output. It will make your life much harder.
Just to mention that every advice you got in previous posts was correct, so I'm just adding additional measures.
This is oversimplified suggestion/answer:
1. Take S/FTP cable, that is long enough, so you can avoid passing near power cables. If you need to pass near power cables, try to do it with 90 degrees.
2. Be sure that every GND on PLC and its modules is directly referenced to ground. Avoid loops.
3. Be sure that HMI GND is directly referenced to ground.
4. Be sure that VFD GND is directly referenced to ground.
5. Be sure that all shielded signal cables have shield connected to GND, but on only one side.
6. If grounding system is TN-C, than make it TN-C/S in you enclosure, by converting PEN to PE and N. Earth connector should be at least same size as supply cable.
7. Check motor grounding.
8. Add isolating transformer for control line 400/230V.
9. Make sure that Fault Ground and Logical Ground are different wires.

Hi,

Thank you so much for taking the time to answer. I always learn a lot from here.

Please also advise, should the '0VDC' of a 24VDC power supply also be connected to ground?

 

[goghie]

Most definitely yes.
In reality there is no real 0V, but only 0V referenced to something, and that something should be ground.
But you should keep in mind, that if you don't take care of grounding, EMC, harmonic distortion, etc. through that 0V to GND connection "problems" will return.