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SC LED on Expansion Units Light UP

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I am using a V130 T2 with an EX DI16A3TO16 + IODI16A3TO16 X 2, in a panel along with 6 VFDs. The PLC wiring and the VFD wiring is seperate. Only 2 Inputs per VFD are being used by the PLC. For the past 2 months everything was fine, but today, I witnessed the SC LED on each of the Expansion Units lighting up. After doing the laborious process of disconnecting each output, it was found that switching OFF the VFDs eliminated the problems.


I realise that VFDs do give rise to harmonics. How do I avoid this?


Awaiting a quick reply



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I'd check your grounds first.  Might have a ground loop that you didn't know about or possibly you're not grounded out correctly.

In order of what I would check:


1) Grounds
2) Test with a power line filter on the PLC and VFD if you have one available, This

3) Isolate each VFD separately and see if the problem returns, perhaps one drive is going bad.

4) Power supply, try running the VFD from a separate plug/panel receptacle if possible.


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All VFDs create noise. You can usually specify the "carrier frequency".  This changes the speed the IGBTs of the VFD fire to make a better sine wave signal.  The higher the carrier frequency the more noise is created.  Mot of the noise that you find relative to VFDs actually comes from the motor being driven and not the VFD itself.  If you have motor grounds connected back to your VFD/control panel you can try grounding the motors on a dedicated ground line seperate from the VFD/control panel.  Your main VFD panel must also be grounded.


Don't forget the small stuff.  You can have all these VFDs and believe them to be the reason and find out that a single motor starter/solenoid valve/cooling fan, any inductive load can cause your problems.  See the post labeled "problem with V1210" from started Dec 18 2014 and you will fing part numbers for noise reducing components for Ac and DC laods.  Oh if you have a mechanical thermostat for your VFD cooling system the contacts on the thermostat can bounce badly and cause all of this also.  An AC noise canceling device (assuming AC fans) placed accross the thermostat contacts will remove this (if it has anything to do with it).


PS: the probability that this is being caused by one VFD going bad is virtually zero percent, but it can be one VFD going to one motor that in combination is the large contributor.

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Thank you for the replies.

The scenario is thus.

6 VFDs all in one panel along with the V130. The motors are 20 meters away. At any given time only one VFD operates. The SC LED lights up on any operation of any of tyhe 6 VFDs.


Have just finished re routing and separating the PLC wiring from the VFD wiring. Will check out firstly with this and additionally will reduce carrier frequency. Will inform the forum of the results



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