Zelio and weird noise problem

I have a panel that was retrofitted with a Zelio PLC and a 100HP Parker 590 DC drive.

The panel has been having trouble for months with the machine randomly stopping as the machine is ramping up. The drive ramps up in 90 seconds and the drive is in current limit for most of it. I finally was able to be there yesterday when the machine finally "stopped". It turns out during the ramp up the PLC was resetting just like you interrupted the power to it.

I trended the voltage going to the PLC during the ramp and the lowest it ever got was 111V. The PLC is fed off a 1kva control transformer on the same supply as the DC drive.

I set the current limit in the drive to 0 and started it about a dozen times with no problems, as soon as I raised the current limit high enough to actually start the machine turning the PLC would reset.

I solved the problem by installing an isolation transformer between the control transformer and the PLC but I am left wondering what the heck was actually going on?

Anyone?

Yes I understand it is a problem with noise triggered by the SCR's in the drive. When I say "elefctrical noise" some people ask for specific details and I don't have them.

DC (and AC) drives cause electrical noise when the transistors switch on and off rapidly. This noise gets fed back into the incoming power to the motor drive. If that power is used for other purposes, it can cause problems as you found out.