# Powerflex 755 Output Phase Loss



## John Valdes (May 17, 2007)

Do you know how to test the input diode bridge and the output transistors? What overloads? You have redundant overloads on the load side?
This is where I would start.

Do you have a manual for the drive? If the input, output test is not included call the distributor you bought the drive from.
They should have the flow charts and basic component testing procedures they can get to you.

Please fill out your profile. Most guys here will not help you unless you do.


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## gpop (May 14, 2018)

Drive seems to be saying that one leg is no longer putting out the same amps as the others so it considers you have a dropped phase.. . ..how many points between the drive and the motors are there. If you have mutiply motors run one at time to see if one is bad (ohm them first)


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## MDShunk (Jan 7, 2007)

Is this drive serving multiple motors? Your use of the term "conveyor line" and "all of the overloads" when referring to one particular powerflex drive makes me think this is a multimotor configuration. Are the overloads on the output side of the VFD? Have your put your eyeballs on the connections in any local disconnects and the makeup in the peckerhead?


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## Brandon Odom (Sep 25, 2018)

This drive is serving multiple motors through a motor protection panel(mpp). The feed goes: vfd-mpp disconnect-thermal protection breakers(12)-motors. Each motor has its own breaker. We have checked the resistance/continuity of all the breakers and the disconnect and they all read fine. We also performed some thermal imaging of the drive and the mpp and did not observe and excessive or imbalanced heating.


We did check the input rectifier and the diodes show to be functioning properly. DC bus voltage is maintains at about 670 volts, so we ruled the bridge out. We have not been able to test the output IGBT's. Since this happens so intermittently, my suspicion is that one of the IGBT's aren't firing for some reason. So like right now the drive is running fine, but it may experience this issue again tonight, tomorrow or next week. All we can tell right now is that yes we are in fact losing one of the output phases since it trips all 12 breakers in the mpp.


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## just the cowboy (Sep 4, 2013)

Are there any contactors on the output side? 


Just saw your post, check connections at main drive to motor OL units for fall of potential, otherwise I agree it is in the drive since all 12 trip.


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## JRaef (Mar 23, 2009)

I take it the PF755 displaying a Fault #21, "OutputPhaseLoss" then? Do you know for sure that no current is flowing from the VFD output? If you can't tell because of the fault, set parameter 444 to a Zero, which will ignore the fault and allow the drive to keep running so you can test it with a clamp-on ammeter. If one phase of the drive is dead, you likely have to replace it.


Back to the multiple motors on the outputs; are you starting and stopping them all via the VFD, or are you starting and stopping them independently down stream of the VFD?


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## gpop (May 14, 2018)

Brandon Odom said:


> This drive is serving multiple motors through a motor protection panel(mpp). The feed goes: vfd-mpp disconnect-thermal protection breakers(12)-motors. Each motor has its own breaker. We have checked the resistance/continuity of all the breakers and the disconnect and they all read fine. We also performed some thermal imaging of the drive and the mpp and did not observe and excessive or imbalanced heating.
> 
> 
> We did check the input rectifier and the diodes show to be functioning properly. DC bus voltage is maintains at about 670 volts, so we ruled the bridge out. We have not been able to test the output IGBT's. Since this happens so intermittently, my suspicion is that one of the IGBT's aren't firing for some reason. So like right now the drive is running fine, but it may experience this issue again tonight, tomorrow or next week. All we can tell right now is that yes we are in fact losing one of the output phases since it trips all 12 breakers in the mpp.


Common one where i work would be for this to happen after maintenance or cleaning. 
One disconnect used to lock out a complete line (between drive and panel) that just happens to be sticking. Doesn't stick for a electrician as they tend to be a lot harsher with the handle.


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## MDShunk (Jan 7, 2007)

gpop said:


> Common one where i work would be for this to happen after maintenance or cleaning.
> One disconnect used to lock out a complete line (between drive and panel) that just happens to be sticking. Doesn't stick for a electrician as they tend to be a lot harsher with the handle.


I get that one a lot. Particularly with rotaries. One pole only half-ass closed. Either that, or the thing is full of water like an aquarium. We stock the guts for them and probably do 2 a week.


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## just the cowboy (Sep 4, 2013)

JRaef said:


> I take it the PF755 displaying a Fault #21, "OutputPhaseLoss" then? Do you know for sure that no current is flowing from the VFD output? If you can't tell because of the fault, set parameter 444 to a Zero, which will ignore the fault and allow the drive to keep running so you can test it with a clamp-on ammeter. If one phase of the drive is dead, you likely have to replace it.
> 
> 
> Back to the multiple motors on the outputs; are you starting and stopping them all via the VFD, or are you starting and stopping them independently down stream of the VFD?


That was going to be one of my questions about not tripping the drive. I'm thinking that it must be in that override mode for all 12 breakers to trip timewise.


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## gpop (May 14, 2018)

Are the breakers the ice all in one type with built in overloads and single phase protection?


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## paulengr (Oct 8, 2017)

Did you test the motors or the wiring going to the motors? Ground fault? Shorted turns?


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