CNC plasma noise with new transformer

Esracerx46 · Nov 5, 2020

My old transformer was a 480 delta primary 240 Delta secondary. We had it in reverse and it worked for years. The only thing it powers up is our 480v overhead crane. One day the crane doesn't have east/west. But has up and down and north/south. But it sounds funny. Sounds funny because line to ground was 230, 304, and 334. Shut the transformer off for a while, fired back up and got more balanced numbers, Delta leg aside. Worked for a bit then acted up again. Decided the transformer was on its way out. Found a 240 Delta primary 480 wye secondary that was available. Direct replacement was 2 weeks plus out. Got the new transformer up and wired. All legs are balanced, crane works great. Until I run the plasma, then I lose east/west function again. Shut the plasma off and the crane works again. Talked to the crane manufacturer and they seem to think the plasma is either backfeeding or noise. Was hoping someone smarter than me here could help me out. Never had this problem with the old transformer

DDoug · Nov 5, 2020

Esracerx46 said:
My old transformer was a 480 delta primary 240 Delta secondary. We had it in reverse and it worked for years. The only thing it powers up is our 480v overhead crane. One day the crane doesn't have east/west. But has up and down and north/south. But it sounds funny. Sounds funny because line to ground was 230, 304, and 334. Shut the transformer off for a while, fired back up and got more balanced numbers, Delta leg aside. Worked for a bit then acted up again. Decided the transformer was on its way out. Found a 240 Delta primary 480 wye secondary that was available. Direct replacement was 2 weeks plus out. Got the new transformer up and wired. All legs are balanced, crane works great. Until I run the plasma, then I lose east/west function again. Shut the plasma off and the crane works again. Talked to the crane manufacturer and they seem to think the plasma is either backfeeding or noise. Was hoping someone smarter than me here could help me out. Never had this problem with the old transformer

Might be nice to list what brand & model & type of "plasma cutter".

How is your grounding on the table, the power supply, and so forth ?

JST · Nov 5, 2020

Well, heck yes, the plasma system is creating electrical noise, and apparently the crane has little or no protection, which sounds to me like a safety problem. Cranes that malfunction are usually bad Juju.

Is the crane newer, with electronic controls? I assume so, old cranes are near bulletproof in that way.

I'd get with both of them, and if possible have them talk to each other. It's not something you really want to be the troubleshooter on, because then it is all your fault.

memphisjed · Nov 5, 2020

we have had to sink multiple grounds multiple times for our plasmas (260 hd's). when the water table changes with the river enough times the ground rods loose ground. It seems that the plasma machines are most touchy about this. change out your plasma coolant too, sounds odd- but as it gains conductivity with grit you fight the noise a lot more- it is enough to mess with welders on separate circuits 40' away. The ground fault is likely just enough to prevent your cranes brakes from disengaging, if you have a low speed override function you can test this. If you have remotes for the cranes, then just a hard reset (circuit off for a few minutes) is enough to get it going again.

Esracerx46 · Nov 6, 2020

It's just an TD A-120 plasma, so no high frequency. But I do have an earth ground sunk right next to the plasma. The crane is a 2017 RM SX series. Power to the plasma is 240 Delta. 240 Delta is the primary on the transformer as well. 480 Wye secondary.

SomeoneSomewhere · Nov 6, 2020

Ground rods shouldn't have much to do with this. I'd be making sure that all your grounds inside the building are actually continuous (especially if conduit is used as the grounding path), and that each separately derived source (i.e. transformer) has the neutral securely bonded to ground exactly once.

A loop impedance meter would be excellent but unfortunately no-one in the US seems to have them.

DaveKamp · Nov 12, 2020

Esracerx46 said:
It's just an TD A-120 plasma, so no high frequency.

It generates a wonderful arc, which in and of itself, is an intense generator of wideband HF noise. Turn on an AM radio, set to the strongest local station, and listen when the plasma fires up. ;-)

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