harmonics?

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one other thing..... when the vfd trips out it is always om under voltage and we push the reset button the contactor pulls in but won't hold. after sometime later ,hours later the contactor pulls in and the vfd resets itself. just though i put that out there .

thanks to everyone for their responses .
 
ohmhead said:
Well thanks for the response , yes today IGBT s but in 1990 thats old so i was thinking scr as they were popular back then.
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The OP was 1990s inferring sometime between 1990 and 1999. I don't think SCRs were in common use for inverters at that time. I can't say that none were but I know that we were marketing a mature IGBT based inverter in 1992, and possibly earlier.
ohmhead said:
I agree 3rd harmonics are neutral related and straight 3 phase non neutral is high 5th to 7th ect ect , so we are now at a point of saying no the vfd is fine and the problem is in the neutral of the service ?
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It could be either, or neither for that matter. If one phase or even one leg of the inverter input bridge was not conducting that could be the source of third harmonic regardless of whether there is a neutral connection. Single phase rectification, whether line to neutral or line to line, results in third harmonic.
 
mickeyrench said:
one other thing..... when the vfd trips out it is always om under voltage and we push the reset button the contactor pulls in but won't hold. after sometime later ,hours later the contactor pulls in and the vfd resets itself. just though i put that out there .
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If you haven't already, can you check the input current balance when the VFD is running?
 
Contactor

Contactor

Are you using a input contactor?

I assume you verified voltage and current on all three inputs to the drive so your not missing a phase input. Such as when a set of contacts are not closing.
 
today i rechecked the 2 vfd and found both had 180hz at the input of the vfd's and at about 15 ' away the cb feeding each vfd i took a reading ,the vfd without any trouble had 60 hz at its cb. the vfd which is giving trouble still had 180 hz . also i found a wire about 1/o that appears to be bonded to the 2 cb buckets that feed both vfd's or it a ground going to the ground connection, i can't tell, it had 5.6 amps and 60hz on it. i checked it twice. thanks again
 
Besoeker said:
The OP was 1990s inferring sometime between 1990 and 1999. I don't think SCRs were in common use for inverters at that time. I can't say that none were but I know that we were marketing a mature IGBT based inverter in 1992, and possibly earlier.
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Except for larger drives, above 25HP, I think all the new generation VFD's I sold back in the mid 80's where Gate Turn Off Thyristors (GTO), Power Transistors, and IGBT's with simple diode bridge input sections.
 
mickeyrench said:
today i rechecked the 2 vfd and found both had 180hz at the input of the vfd's and at about 15 ' away the cb feeding each vfd i took a reading ,the vfd without any trouble had 60 hz at its cb. the vfd which is giving trouble still had 180 hz . also i found a wire about 1/o that appears to be bonded to the 2 cb buckets that feed both vfd's or it a ground going to the ground connection, i can't tell, it had 5.6 amps and 60hz on it. i checked it twice. thanks again
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Did you check the current in each of the three phases going into the input of each VSD?
 
mickeyrench said:
yes, all were within a couple of amps from each other. thats the first thing i checked.
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That's good. It indicates that the input rectifier looks OK.
Can you get at and measure the voltage across the DC link?
For a 480V 3-phase supply, it should be in the region of 650Vdc and it should be the same on both of the 55kW VSDs.
 
not till tuesday at the earliest. do you think a bad board would keep the vfd from reseting for a few hours or could it be external devices? pilot light says vfd failure, motor alone has 3 devices, heaters , bearing temp. , and a heater inside motor for condesation. the print is just to large for me to trace. thanks for your time.
 
mickeyrench said:
not till tuesday at the earliest. do you think a bad board would keep the vfd from reseting for a few hours or could it be external devices? pilot light says vfd failure, motor alone has 3 devices, heaters , bearing temp. , and a heater inside motor for condesation. the print is just to large for me to trace. thanks for your time.
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Are the two VFDs fed from different boards?
I suppose a bad board could prevent the VFD from resetting if there was maybe a loose connection on one phase for example. That doesn't sound like a problem that would take hours rectify itself - you might expect that to show more of an intermittent or random nature.

Maybe a summary of where we think we are at and what we know:
  • The Fluke meter displays 180Hz. Was the drive running or stopped at the time?
  • Only one of the two VFDs trip.
  • The trip indicated is always undervoltage.
  • That trip occurs when another machine is started across the line.
  • When the drive is running, input current balance is within a couple of Amps which would be just a few percent of rated current.
  • The drive self-resets after a few hours.

And maybe I have missed some things but, from the list, it looks there are at least two connected events.
Another machine is started and one of the VFDs trips on undervoltage. Starting the other machine direct on line would dip the voltage some. Maybe one VSD undervoltage is set slightly differently to the other?
And maybe there is more than one fault.

Just some thoughts.....
 
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