Yes, I concur on the cabling parallelling being an issue. I can't do anything about that one without a lot of work. But I will check both grounds on the cable with the faulty encoder info. Thank youThe orange cable is the drive cable to the motor. It's shielded and the shield attaches to a special clamp at the drive. If that connection is loose or not made right, and the motor has an encoder cable on the same path, that one does, the encoder cable shield is paralleled with the orange cable shield. The encoder cable, green one, can get noisy if the orange cable has a bad shield connection. That's one of the faults it's throwing, noisy encoder.
So we have a piece of equipment that requires 310 amps at 400 V. It is the only piece of equipment on the circuit.
The primary side is supplied by the utility with 240 nominal high leg delta. The transformer is a 225 KVA delta / Wye transformer.
The secondary side is 400 volts WYE. No neutral has been brought to the equipment only three hots and a ground.
The equipment has 30 VFD's with low duty cycles, each rated at 30 Amps. Peak current (200ms) has been 120Amps on each leg.
I have monitored the power for the last month. During this time in operation we consistently get the ground showing intermittent 5.5V. Also current, but I cannot recollect amount (an amp or two?) Internal to equipment there is a transformer 400/24 transformer. The VFDs are fed by a power supply, measuring from the VFD to the ground bar, I show 45 ohms while running. The metal case (also supposedly grounded to the bar) only shows 2.6 Ohms.
Total harmonic distortion (current) ranges from 45-70% - which I think contribute to the voltage on the ground.
When turning on, random VFD's will trip going into error conditions. This goes on for about 45-135 minutes. After which the equipment runs all day without incident.
Random problems always brings to mind grounding issues.
I suspect that the voltage on the ground is causing the trips.
Question: What avenue would you attack this?
1). Bring a neutral, with the idea that this would allow us to cleanup the ground? (Does that even make sense?)
2). Install line reactors, with the idea that lowering the harmonic distortion by 10% would result in less voltage on the ground.
3). Same argument as #2, except active filtering would lower the distortion down to 5-8%. (much more expensive).
4). Something else?
Appreciate the thoughts
Right, I was reading about a device that delays start up, as an alternate to a line reactor.Ok so chances are those are diode front end VFDs which typically have some pretty awful line performance. A line reactor blocks triplen harmonics but those aren’t the harmonics tge VFDs create so that is a waste of time. Essentially you have been given bad advice. Current harmonics are HARMLESS unless it’s affecting the transformer. Look at it this way. You have a 225 kVA transformer. If the load is purely sinusoidal then the usual rating system works. But it’s not. With harmonics there are times where you are drawing more current than simple sine wave math predicts. If the transformer load is below the rated current then it won’t distort the output. If it’s above the rated current voltage starts to drop and the more you exceed the rating the more the output sags. If this happens you get voltage harmonics, which is NOT harmless and what we need to avoid.
Where there are issues is two things. First off the transformer short circuit rating is pretty close to what I suspect the VFDs are rated for. So unless they have fast fuse protection or something like that you’ll get a lot of VFD failures where something as simple as a motor failure causes a VFD to fail. This is where a 3% line reactor or splitting them up among multiple transformers can make a difference and leads to what is probably your issue.
So I don’t know the ratings and how it’s timed but I’m estimating 21 kVA each? 400 x 30 x 1.732 is 21 kVA. At 30 drives that’s 630 kVA. I’m not so concerned about operational issues when it’s running as you said that seems OK. But when all those drives initially power up you have every drive trying to precharge simultaneously. I have serious concerns you’ll get all kinds of boot up glitches as the line voltage takes a dump when this occurs, which is what you describe. A simple test is hook up your meter on alligator clips and watch line voltage (phase to phase) looking for minimum voltage. I’ll bet it’s dipping low causing momentary power losses causing malfunctions in the electronics (think intermittent power failures to 30 tiny computers). A better strategy is to power them up in stages. Often machine builders neglect this or feel you should just leave it powered up 24x7 and reboot a few as needed. A 1500 kVA transformer would do much better but again cause even worse short circuit issues. So you can use contactors and possibly power things up in stages with timers/PLC logic or get more smaller transformers.
- these same errors are occurring on multiple drives. About 1/3 of all drives have no errors. The remaining have multiple iterations of the errors listed above.
- drives 1-21 are in use. Drives 22-28 are never used, (duty cycle of 0); the errors occur even though the drive is not used.
- cannot disable the unused drives.