Overvoltage fault.

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ptonsparky

ptonsparky

Tom
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
We have a VFD we installed last year that is suffering from over Voltage trips as of today. Lineside reactor is installed and is matched to the drive by the MFG. The drive feeds either of two auger motors via IEC style contactors. They are electrically and mechanically interlocked and must be closed two seconds prior to the drive operation. Drive stops four? seconds prior to the contactors opening. Coast to stop, which is almost immediate.

The times we have had overvoltage in the past it was PFC switching by the POCO, solved by line reactors, or ramp to stop with too short of ramp time. We have not been there yet but the operators are suggesting a relationship to a frequently cycling fractional hp motor. Could the starter coil on it be causing the grief a couple hundred feet away? This may be the first day they have both been run.
 
G

gar

Senior Member
Location
Ann Arbor, Michigan
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EE
170213-2423 EST

ptonsparky:

If overvoltage tripping is strictly a result of the VFD capacitor bank voltage, then look for that cause. Put a voltmeter across the capacitors, and see what the voltage is vs time.

As you pointed out a fast deceleration can be the problem source. If powerline source voltage is high, then this in combination with your normal decel could cause excessive capacitor voltage.

A small external motor won't have much affect on the VFD capacitor bank voltage.

Our CNC machines have a resistor that is shunted across the capacitor bank when the voltage rises too much during decel.

.
 
kwired

kwired

Electron manager
Location
NE Nebraska
Two main reasons for this error is too rapid of deceleration and too high input voltage.

If you are set for coast to stop it shouldn't be deceleration issue, so you probably are going to need to look at input voltage.
 
Jraef

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
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Electrical Engineer
I agree. The common issues are having the drive set for controlled decel and trying to do that too fast, or the line voltage is actually increasing. Totally eliminate those possibilities first.

As my step grandfather the farmer used to say; "When your crop is being eaten by something in the night, you have to eliminate the possibility it was mice or rabbits before you start chasing elephants and unicorns."

The small single phase motor would be a unicorn here, in that it doesn't exist anywhere. The elephant in your story, meaning it exists but is highly unlikely to be at your farm, is that sometimes there can be a resonance issue with nearby capacitors that are interacting with your drive's capacitors and creating a little tank circuit of sorts, which can result in an over voltage on the bus. Usually a reactor will eliminate that, but every once in a while there is a high frequency resonance that gets through, ie an elephant that escapes the zoo. Look around for PoCo caps that they sometimes use to boost line voltage on long runs, like those going out to farms. Also look for leftover PFC caps on other things nearby that are on-line even when the machine they were installed for is not or is even gone. I just came across that recently, there was a set of caps installed for an air compressor and because the compressor ran 24/7, the caps were just connected to the line, not below the contractor. When they changed to a bigger VFD driver compressor, they forgot about the caps and left them connected all the time. Every VFD in the plant kept eventually triipng on OV, often even when not running at all, just connected and powered.
 
Sahib

Sahib

Senior Member
Location
India
ptonsparky said:
We have not been there yet but the operators are suggesting a relationship to a frequently cycling fractional hp motor. Could the starter coil on it be causing the grief a couple hundred feet away? This may be the first day they have both been run.
Click to expand...
May be the cause because a motor on the output side of VFD drive cycling independent of VFD drive control might cause voltage spikes as even a disconnector on the drive output side is not permitted for same reason.
 
kwired

kwired

Electron manager
Location
NE Nebraska
Sahib said:
May be the cause because a motor on the output side of VFD drive cycling independent of VFD drive control might cause voltage spikes as even a disconnector on the drive output side is not permitted for same reason.
Click to expand...
I don't think the single phase motor mentioned was connected to the drive output - he was just wondering if it would cause any problem via the input of the drive.
 
ptonsparky

ptonsparky

Tom
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
Well that was interesting. I was watching the bus Voltage of about 640 when a drag motor kicked on and the VFD tripped on OV. The motor is 10 HP or above. I have not crawled up to it yet. I did not see a PFC for it but it could be hiding somewhere. Offending motor is electrically a couple hundred feet away. I'll take my toys along and see what we get this afternoon.
 
Jraef

Jraef

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Staff member
Location
San Francisco Bay Area, CA, USA
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Electrical Engineer
ptonsparky said:
Well that was interesting. I was watching the bus Voltage of about 640 when a drag motor kicked on and the VFD tripped on OV. The motor is 10 HP or above. I have not crawled up to it yet. I did not see a PFC for it but it could be hiding somewhere. Offending motor is electrically a couple hundred feet away. I'll take my toys along and see what we get this afternoon.
Click to expand...
Huh, any chance the drag motor IS somehow connected to the VFD output? Being a single phase motor, the starting cap may be the culprit even if it is a fractional HP, you can't have anything with caps connected to the OUTPUT side of a VFD (unless dampened by an winding, like on a PSC motor). I can't imagine a little starting cap on the LINE SIDE having an effect from a couple hundred feet away.

But then again, are the conductors for that little motor run in the conduit with the VFD output conductors? Line capacitance may become an issue in that case too. Just hunting nocturnal elephants here...
 
J

jim dungar

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Staff member
Location
Wisconsin
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PE (Retired) - Power Systems
I think it would help if the OP clarified what is connected to to the line side of the drive and what is connected to the load side.

I fear we are solving problems that do not exist.

I understand it to be:
Drive feeds one of two auger motors at a time.
Drive has a input line reactor
Somewhere in the building there is a single phase fractional HP motor that cycles.

Now we hear about a drag motor that is maybe 10HP, which means it is probably 3-phase and across the line starting.
 
ptonsparky

ptonsparky

Tom
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
Done. The larger motor had just happened to start at the same time as the problematic .33 hp 480v sewing machine. The limit switch that started the sewing machine was out of adjustment. It would cause starter for it to cycle rapidly for a second or less. That resulted in 840 to 860 VDC at the D.C. Bus. 1 msc peak. Adjustment and a rubber band for now works.
 
J

jim dungar

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Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
ptonsparky said:
Done. The larger motor had just happened to start at the same time as the problematic .33 hp 480v sewing machine. The limit switch that started the sewing machine was out of adjustment. It would cause starter for it to cycle rapidly for a second or less. That resulted in 840 to 860 VDC at the D.C. Bus. 1 msc peak. Adjustment and a rubber band for now works.
Click to expand...

Now you have me wondering.
Where is this fractional hp motor, on the output or the input of the drive?
 
ptonsparky

ptonsparky

Tom
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
Saturn_Europa said:
Nice!! Glad you found it.

How did you catch it? Did you hear the contact chatter? Those intermittent problems are the worst.
Click to expand...
I had one meter at the VFD with another looking for transients on the drag starter where my help was at. He could also watch the HMI that has indicators as to what is running. We have no control of the sewing machine but he could see the VFD stop when he heard the sewing machine starter chatter.
 
Sahib

Sahib

Senior Member
Location
India
I think one of harmonics generated by VFD is causing resonance thereby high input voltage to the drive. Conduct a harmonic analysis, check adequacy of existing line reactor and replace same with suitable one, if found necessary.
 
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