milldrone said:
The only reason I mentioned the VFD's is I saw you mention them in post #9. When ever I have something strange happening and there are VFD's nearby. I suspect them first.
One of the most important things for noise supression is distance. Never route VFD supply or motor leads near any other wiring. Second is shielding. Surround any motor leads with screened cable or conduit and ground at both ends and be sure to follow the VFD manufacture's recomendations for gounding.
We used a 14/4 VFD shielded cable and tied the shield on one end to ground. This is what was recommended. The distance is close to borderline on a couple of motors but the rest are fairly short runs.
[/QUOTE]If you are already good in these departments or can't change what you already have in place.[/QUOTE]
It would be hard to change any existing wiring in the field part but something cold be done in the PLC panel or the VFD panel.
[/QUOTE] Then a little load like a pilotlight or resistor may work sometimes finding the right ammount of load can be tricky. That's why it's best to do the distance / shielding thing first.[/QUOTE]
How would I go about figuring out the proper size resistor. we do not have a lot of things here to work with. I will have to purchse whatever we need locally.
[/QUOTE]I just thought of another quick test. When the eyes / PLC inputs are malfunctioning can you remove the power to the VFD's?[/QUOTE]
I can do this. I hope to get out to that system in a few minutes.
[/QUOTE]I'm curious is your 480 volt supply a floating delta? or high resistance center tapped Y? These types of transformer connections and VFD's can cause some very odd behavior. The noise the VFD makes wants to get back to the transformer any way it can find. I have never seen this but I can imagine that a 240/120 delta with a wild leg would also exhibit some strange behavior when a VFD was used. If you do have one of these type of transformer connections. Then My recomendation is to get a drive isolation transformer so that a proper grounding scheme an be employed.[/QUOTE]
The system transformers are delta primary and wye secondary. The 480 volts would be delta and 240/120 would be wye.Other than the 480 volt to the drives for the motors it would be 120 volt or 24 VDC.
An isolation transformer would be expensive wouldn't it? This is a small project but several motors are on it but only 6 photeyes at this time. The project may grow later. Any cheaper suggestions or other things to check first?
