DC Overvoltage fault

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ptonsparky

ptonsparky

Tom
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
This might have been better placed in engineering.

P1000.

Fault occurs at initial start and ramp Attempt. It ran fine two weeks ago.

Chatted with an excellent support person that pointed to a motor issue. Quick check with Fluke tester showed windings grounded. If it beeps there is no reason to get out the Megger.

Why over voltage vs a ground fault?
 
ptonsparky said:
This might have been better placed in engineering.

P1000.

Fault occurs at initial start and ramp Attempt. It ran fine two weeks ago.

Chatted with an excellent support person that pointed to a motor issue. Quick check with Fluke tester showed windings grounded. If it beeps there is no reason to get out the Megger.

Why over voltage vs a ground fault?
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did you disconnect the motor from the drive before checking the resistance to ground with your fluke? chances are there might be a capacitor from each line to ground and the fluke would show that as a dead short.

my guess is you are trying to start with an overhanging load of some sort and the excess energy is being backfed into the DC bus. it does not take much for an overvoltage. I suggest pulling up the DC bus voltage on the display and seeing if it starts to climb when the motor starts.
 
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A ground fault may be causing reflections back into the VFD's output, and that energy is then conducted through the protection diodes for the IGBTs over to the DC bus. That could then charge the DC bus capacitors leading to an overvoltage.
 
ptonsparky said:
Thank You. Other drives indicate ground faults and I’ve dealt with over voltage before but not associated with GF.

Any chance lightning could have done this while the motor was offline? $7K motor two years ago. I’ll be asked.
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Anything is possible. People like to blame lightning for lots of things but it would almost certainly have taken out the drive rather than the motor. I vote for winding failure. When you get it rewound the rebuild shop might be able to tell you what happened based on the damage they see when they rewind it
 
ptonsparky said:
Thank You. Other drives indicate ground faults and I’ve dealt with over voltage before but not associated with GF.

Any chance lightning could have done this while the motor was offline? $7K motor two years ago. I’ll be asked.
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Generally speaking the motor has two kinds of insulation in the stator. All of the wiring has insulation on it to prevent turn to turn shorts. The slots are insulated from the whole coil. A ground fault means the integrity of the slot insulation is damaged. Faults can occur elsewhere but that’s what it is telling you. It is the end result of a motor failure.

With the motor disassembled you can often tell by the damage what happened. For instance if all the insulation is evenly burned, it’s an overload. If it’s only on one phase it was single phasing. If it is only the first couple turns on one coil it was a big surge. If it’s on every coil it was most likely VFD reflections from excessive cable length. If the bearings are “frosted” and they see fluting it’s often a common mode issue from a poor drive filter or cabling issues.

You should get an inspection report from your motor shop. If you don’t, time to start looking for a new one. This is automatic with every motor they receive. They should be running a test (Baker, PdMA, etc.) then pop the bearings out and insoect. Core loss after burnout to check if it can be rewound without restocking the core. You should be using that information to improve your motor installations to get the most life out of them you can. Good shops will generally just document and ignore most common failures unless you ask.
 
I most likely will never see a report. The area well driller stocks rebuilt motors and will have this replaced before I can locate one. This motor was a replacement for the original that had been in place for over 20 years, prior to VFD. Reason we installed a load reactor. Owner was told the replacement had been wound for VFD operation.

My original thought was the shaft was stuck, but you could turn it by hand. It does not feel like bearings at all.
 
Maybe I missed this but what is the motor driving?
Many of the motors I have encountered have been phase-controlled. Others were DC choppers.
 
ptonsparky said:
An irrigation pump. Hollow shaft motor sets above ground and turns pump impellers 200-300 feet down. Small by your standards. 100 HP.
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Yes, I have regularly seen those. Quite a few of these have been motors on the surface with the submersibles several feet down.
Ours were mostly utility water sites. Often around 35kW
Were you using variable speed? Or how else were your motors controlled?
 
Besoeker3 said:
Yes, I have regularly seen those. Quite a few of these have been motors on the surface with the submersibles several feet down.
Ours were mostly utility water sites. Often around 35kW
Were you using variable speed? Or how else were your motors controlled?
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We put the VFD on four years ago so he could have better control of water flow to either a full circle pivot with swing arm or to a a smaller half circle about 1/2 mile away. He had enough water to supply both, if he had wanted, by varying the speed from 55 HZ to 60. Two years later he changed everything and the VFD install was a waste of time and money.
 
ptonsparky said:
We put the VFD on four years ago so he could have better control of water flow to either a full circle pivot with swing arm or to a a smaller half circle about 1/2 mile away. He had enough water to supply both, if he had wanted, by varying the speed from 55 HZ to 60. Two years later he changed everything and the VFD install was a waste of time and money.
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OK.
How did you regulate the flow?
 
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