VFD questions

[Susquatch]

@BaitMaster - Excellent writeup! Very well done.

Your traces look like mine did too. Your peak to peak numbers are even higher than mine but your motor voltage is higher than mine too. I would say we are in the same ball-park.

I fear I may have misled you a bit. I'm not really that concerned about the impact of these spikes on my motor. It's a 1000:1 VFD rated motor with grounded bearings.

My concern is mostly with my DRO mounted on the same machine and stray voltages in the cable making their way into my DRO control box. It's a Chinese box and I have read that it's easily damaged by ground loops and the like. It is not powered by the same 220V power source. It is connected to a totally separate 120V supply on different breaker. And I have input line filtering in the VFD inputs. So it's just those nasty spikes on the output that worries me. I have isolated the wiring, and I have shielded cable but if there is one thing I have learned in my career it is that high voltage spikes have a way of causing mysterious havoc many meters away! Sorry to maybe not have been clear on that.

And especially sorry for precipitating a lot of work on your end.

That said, it's awesome stuff. I particularly like the comparison of various mitigation strategies!

Im going to sit down with a nice cold drink and let your posts settle in. I'm sure I'll have more questions.

 

[Susquatch]

Motor terminals. 80’ of cable. 7.5hp 480v drive rigged up on the bench. Crappy picture but it was fluctuating from 2.05-2.3kV P2P.

NICE Fluke Motor Drive Analyser!

 

[Susquatch]

After our researching of this and acquiring “drive rated” cable, no difference of the waveform was noticed by us when using special VFD cable. I’m sure it makes a difference in interference with neighbouring electronic signals, radios, encoders, etc. If you press the cable manufacturers and dig, 1000v rated Teck type cable is approved for use in 480v drive applications. No difference has been noticed by us at all between the special cable and 1000v teck properly used.

Nice Sine Wave!

Any chance your outfit might be willing to sell me some of that VFD Rated Cable?

Or at least tell me where you got it?

After reading your posts more carefully, I don't really have any questions. Excellent writeup and good conclusions. Well done!

 

[Susquatch]

This is after the 80’ of cable…. After applying a sine-wave style filter. Yes. Satisfying.

OK I lied. I do have a question.

Is there any chance you looked at the VFD's ability to understand what the motor is doing after feeding is such a highly filtered input?

This was a question I asked the manufacturing engineers and never got a reply I was happy with.

Since the VFD measures its own output vs its expectations of the motor during motor characterization, and then uses that information in SLV mode, I was interested to know how feedback from this modified input might affect the VFD'S Ability to interpret the results.

Any insights?

 

[BaitMaster]

@Susquatch I’ll look for that cable…. It’s somewhere lying in a pile more then likely. I believe it was #4 or #2….. so might be a bit big for you.

As far as the SLV stuff is concerned, with the SWF….. I must admit I don’t know. The application is Variable Torque (pumping), and we tried configuring those drives every possible way to get rid of an ongoing motor reliability issue…. So normal Linear V/hz stuff as well as SLV, with tuning for motor etc….. and we went back to V/hz and added the sine filter. The drive does have a sine filter mode, so It might still work.

If the filters get rid of our reliability concerns over a multi year period, (we’re on year 2) then we will invest some R and D to tune them and use vector flux.

Haven’t done too much with CT applications and the SWF’s yet.

 

[Susquatch]

If the filters get rid of our reliability concerns over a multi year period, (we’re on year 2) then we will invest some R and D to tune them and use vector flux.

Haven’t done too much with CT applications and the SWF’s yet.

I kinda figured you were doing some kind of financially important things there as soon as I saw your Fluke meter. It really did blow me away!

I'm not suggesting I can really help but I confess I am curious. What kind of motor reliability problems are you having? Just guessing from a few of your questions and comments and the nature of your testing that it's winding insulation breakdown. I imagine a motor that size is big bucks!

 

[BaitMaster]

I’ll send you a pm tomorrow. Insulation breakdown is correct…

 

[Ironman]

Start by looking at the motor data plate, fairly common for motors to be reconfigurable for different voltages just by changing the connections inside the motor box, the motor plate will shown this if applicable. If not reconfigurable running at lower base frequency seems like a viable solution.

I had a 3ph in and 3ph out VFD and sold it. I would do as you suggested, but will add this info:
A 3phase motor can run at lower voltage with reduced power. When I bought my Lagun it was 600 volt, and made a horrible grinding noise. I was prepared to re-bearing the head. I also wanted to convert the motor to a 220 3phase. So I powered up the mill at 220 volt on my VFD and started listening with the stethoscope. The grinding came from the motor. I boosted the motor off the mill and ran it on the floor and verified it was motor bearings. My point of this blather is you can do it, you can run on lower voltage, I'd re-wire that motor to 220/208 and you are golden.