Drive Fault - Low Voltage Message

My idea is to ask you how's the measured supply voltage of those units against the nameplate.

How long is the wiring from the machine to the mains ?. What wire gauge ?. Do you have a meter ?.

I've seen a voltage drop in machines that are fed from the same panel thru very long wires.

You do not mention rated voltage, what the running voltage is, what on the machine faults with low voltage (is it a VFD or DC drive, or a line monitoring unit?)

Use a line monitoring instrument, and check what the high and low is.

Verify the supplied voltage is within tolerance.

See if a large motor starting is dropping the system.

Check to see what the drop out point is for the fault - it may be set too tight.

Have there been any recent alterations to this set up and is there any possibility that one phase is reversed. I would also advise to make sure that all 10 machines are using the same starting method. Star delta start-up? Are all 10 machines started at the same time. if yes try starting them one by one. If this is a new phenomenon ask what has been recently changed. These might be long shots but have been known to happen. Lets know how you go

I have a machining center that came from Germany. Had a similar problem. Drive would fail indicating low voltage intermittently. A static test of voltages showed them to be okay. Under load the failure occurred when the program called for high machining rpm's. So it was one of these troubleshoot and scratch head days. They supplied a transformer that correct the voltage. What I finally found was the secondary of the transformer was fused. One fuse had not blown but the element had broken under years of stress. It was only under high current draw that the metal of the element would open along the crack.

Would also look at what else these three machines may have in common.

Assuming a VFD, and assuming low voltage (600V or under). Many drives have no Phase Loss protection, but will use the UV trip function to monitor the DC bus average voltage to detect excessive bus ripple as an indirect way of determining that a loss of phase is creating a situation detrimental to the drive. VFDs don't really care much if the incoming power is 3 phase or single phase, all it does is rectify it to DC anyway. But under single phase input you get two issues; the current through the rectifier increases by the sq. rt. of 3 (1.732x), and you get deeper DC bus ripple because there are fewer pulses from the rectifier, 4 vs 6, and those pulses now go all the way down to Zero VDC in between. But if the load is less than half of the VFD size, you will have enough extra capacitance and diode capacity that it will not matter. That's why on some small drives, they don't bother with a phase loss detection circuit, they just monitor the EFFECTS it might entail based on load. So in your situation, it might be that these VFDs are ALWAYS getting single phase power, but they only trip off when the LOAD becomes too much for the capacitors to handle the extra ripple, so that ripple affects the average DC bus voltage and the drive protects itself by tripping on under voltage.

Great suggestions to consider. Hopefully, I will be able to investigate tomorrow. I'm thinking there must be a common issue that has been overlooked by the people on site. It is always nice to have help getting in the frame of mind. Thanks for the ideas!