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VFDs gone wild.

VFDs gone wild.

VFDs gone wild.

(OP)
Had a guy call me about his 5HP VFD.

It's an ABB-AC35503U style running a saw.

He described it as 'acting weird'. When asked to define that he said in both vector or v/hz mode it powers up. When he starts to raise the output frequency above 0.0Hz stepping to 0.1Hz the motor goes to full rated speed (1725) immediately.

I can see some odd parameter settings possibly causing that except in his efforts to troubleshoot this he's taken the VFD and motor to other places in town and it works correctly in those locations. It only malfunctions in his shop. He went on to say he has some crazy imbalances in his power. He told PG&E about it and they came out and examined things and replaced all the transformers supplying the place!

Now his line voltages are (please sit down) 246V, 230V, 254V!!

While this truly sucks I'm still puzzled as to what a diode bridge front-end of a VFD would care about it. I can't see a reason imbalance would bother a VFD other than working the bridge diodes unevenly.

I have to pay this place a visit soon. I'll check the line voltages at the incoming service to make sure the imbalance isn't house-wiring/loading.

Anything else you folks can think of to check?

Keith Cress
kcress - http://www.flaminsystems.com

RE: VFDs gone wild.

Phase rotation or grounding is all I can think of since it works elsewhere. I bet when you do an on site visit, you say Ah ha!

Chuck

RE: VFDs gone wild.

Is he adjusting the frequency with a remote pot that is past its "Best Before" date?

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: VFDs gone wild.

Most likely he has some serious CM noise issues AND he is using a non-isolated analog input / external pot for the speed control, so the VFD is getting what IT thinks is a full speed command. The reason it would work everywhere else is because it is not THIS EQUIPMENT that is creating the CM noise, it's something else in his facility; bad lighting ballast, other drives (especially cheap DC drives), cheap / old power supplies etc. etc.. I'm not that familiar with that drive but in the ACS550 drives you have a parameter that shows you the commanded speed. If you find that and look at it while the drive is running, that will tell you what the VFD is responding to. How that value gets that high is then a process of elimination.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

RE: VFDs gone wild.

(OP)
Thanks folks. I tried to visit today and the guy had dixlexited the number he gave me. I will make it there eventually this week.

I spent today doing this.

GAG!!

Grueling..

6 hours to pull two thousand, two hundred feet of 750MCM in 30 pieces out of 6 conduits by hand - in the dark (no power could be in the building for the fun). I'm shellacked.

Keith Cress
kcress - http://www.flaminsystems.com

RE: VFDs gone wild.

Oh, what a tangled web we weave, when we first practice to deceive pull wires. laughtears

Muthu
www.edison.co.in

RE: VFDs gone wild.

When you get that to the recyclers you'll get a nice boost to the coffee fund.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: VFDs gone wild.

You can probably get more if you strip it first, usually about 50% more by weight, but you lose the weight of the insulation, so the net gain is usually about 20%. but 20% of $8k is $1600. Google plans for a home made wire insulation stripper, they are not that complex. $500 to make one, $1600 gain, it would be worth it in my opinion.
https://www.youtube.com/watch?v=BOZ4_AqUyNs


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

RE: VFDs gone wild.

(OP)
Hi Jeff. 250MCM to 750MCM is 90% weight pure copper which is much better than the usual wire.
Unskinned is selling for $1.5 to $1.6/lb and skinned is $1.9/lb. Still maybe worth skinning it especially since a bunch of free-range machinist's are involved.

Keith Cress
kcress - http://www.flaminsystems.com

RE: VFDs gone wild.

(OP)
I'm back with the status of the malfunctioning VFD.

Recall at this site and only this site the VFD responded to its own pot by displaying 0.1Hz but the motor cranking up to full speed. If the VFD was taken elsewhere it behaved normally.

The building power was grossly imbalanced: 246V,230V,254V

Client complained to PG&E and they brought instrumentation to do a study. They set it up and ran it for 48hrs. Came back and collected it all and left. Next day the guy showed up and showed the results and this after installing all new transformers. Still grossly misbalanced! Way out beyond 3% -> 10%

After reporting this to my client he called a more experienced person who promptly asked, "any capacitors around?".

The agent went out in the street on the phone and looking both ways saw a bank of caps on a pole (regulator) about 3 poles down the street. He went down to them and found one to be failed open. He ran and got a replacement called dispatch and said, "drop this circuit now".

Dispatch: "Are you crazy that's over six hundred commercial/industrial customers."

Lineman rebuttal: "Would it be better to have 600 burned out motors?"

Dispatch dropped the circuit.

It took about 30 minutes to replace the cap.

Power brought back up.

Now my client has about 3% imbalance possibly caused by transformer tap games trying to get him balanced prior to fixing the regulator. This will be checked this week.


Meanwhile with only 3% imbalance he tried his VFD and it works correctly now...

I cannot really square this with what I know. I'd expect the 'dumb' bridge rectifier front end to care little about imbalance, charge the DC bus and the VFD to run off the DC link and know nothing about a simple imbalance.



Keith Cress
kcress - http://www.flaminsystems.com

RE: VFDs gone wild.

Strange. Given that most VFDs with simple front ends will operate on single phase, you would think that they would accept a voltage unbalance. I would expect the first result of a bad unbalance to be an overloaded and failed rectifier.
To quote crshears from another thread;

Quote (crshears)

"no voltage is better than low voltage,"

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: VFDs gone wild.

My guess would be that this is one of the VFDs that take their internal control power from an AC/DC power supply connected to the line terminals, as opposed to the majority that tap off of the DC bus with a DC/DC chopper type power supply. The AC supply concept was used by some less expensive drives for a while but was susceptible to line noise and spikes, which is why most mfrs abandon it.

Oh wait, you posted that it was an ACS355, I don’t think they do that. Huh...


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

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