# Troubleshooting VFD's



## MDShunk (Jan 7, 2007)

Your VFD has a coil?? Or, do you mean the virtual coil in the relay logic?


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## dronai (Apr 11, 2011)

The motor starter coil in the MCC.


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## eric7379 (Jan 5, 2010)

dronai said:


> The motor starter coil in the MCC.


The motor has a starter and a VFD? Or is the starter upstream of the VFD and just the control side of the VFD is energized until the starter pulls in?

Usually with Profibus connection faults, there will be a Profibus communication error message at the HMI, depending on how well engineered the system is. By the sounds of it, your system is a well engineered system, so I would be surprised if there was no Profibus communication error message. 

Are these all Siemens drives?


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## dronai (Apr 11, 2011)

eric7379 said:


> The motor has a starter and a VFD?
> 
> 
> Yes, maybe I'm saying this wrong. MCC layout for all is power wiring thru an overload, then to a control relay. Then to the VFD which is located about 15' from the motor. Everything is controlled by the PLC. My problems have been at the VFD's.
> ...


 YES 

- How long will the error message stay ? We only found a fault indication light with no message.


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## nolabama (Oct 3, 2007)

You have a made starter but your VFD is not enabled?


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## dronai (Apr 11, 2011)

nolabama said:


> You have a made starter but your VFD is not enabled?


 

Yep !!! This one was the Profibus connection we think. Maybe that's why nothing is being reported back to the HMI.


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## nolabama (Oct 3, 2007)

dronai said:


> Yep !!! This one was the Profibus connection we think. Maybe that's why nothing is being reported back to the HMI.


Control power has been sent to starter but PLC is not sending start command to VFD . This will result in no fault sent to HMI. It sounds like a communication issue.


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## JRaef (Mar 23, 2009)

nolabama said:


> Control power has been sent to starter but PLC is not sending start command to VFD . This will result in no fault sent to HMI. It sounds like a communication issue.


One possibility:
If you have a starter ahead of the VFD, that means the VFD is powered down. If the profibus command goes to the starter to close it and to the VFD at the exact same time, profibus will detect that the VFD is not there because it tried to talk to it before it came alive. You would have to not send the profibus VFD command until you know the starter pulled in. 

It might be set up that way, but here's the problem. If the design uses Simocode relays for the profibus control of the starter, a Simocode isn't usually hard wired to contactor auxes. The normal Simocode interlock looks for current flow to know that the starter engaged. But if you are feeding a VFD and the VFD is not on, then there is no current flow and the Simocode may not be allowing the PLC to send the VFD command. 

Putting starters ahead of VFDs is not a good idea so someone unfamiliar with the pitfalls may have unknowingly made a programming error.


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## nolabama (Oct 3, 2007)

I have no experience with starter upstream of VFDs. Sounds like your asking for trouble.


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## nolabama (Oct 3, 2007)

As to the over temp motor, does the VFD have thermal overloads in them?


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## John Valdes (May 17, 2007)

JRaef said:


> Putting starters ahead of VFDs is not a good idea so someone unfamiliar with the pitfalls may have unknowingly made a programming error.


He is saddled with this upstream contactor. It looks to be used for E-Stop and E-Stop only. It also is controlled by a off delay timer to prevent jogging of VFD power. Some are jumped out for the apparent reasons. I encouraged him to remove these jumpers and allow them to work as designed. I have him checking some operational stuff tonight so we can get a bit more familiar. 



nolabama said:


> I have no experience with starter upstream of VFDs. Sounds like your asking for trouble.


I don't like it either, but the engineer (designer) wanted a "fail safe" E-Stop. I guess? :whistling2: 
I know we could have done it differently and much less expensive, but he has what he has. It has already been designed, commissioned and is currently operating.



nolabama said:


> As to the over temp motor, does the VFD have thermal overloads in them?


The motors are connected with three wires, so it is safe to say motor temperature was not considered.
However, he is using Baldor Super "E" motors. They come stock with thermal overloads. I guess they are not connecting them.
*Dorian*. Right? You leave the two leads marked P1 and P2 disconnected when you replace a motor?


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## j johnson (Jul 20, 2009)

On some vfd the thermil probe input must be jumped as a thermel switch dose.


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## John Valdes (May 17, 2007)

j johnson said:


> On some vfd the thermil probe input must be jumped as a thermel switch dose.


Or the function can be turned off in the parameters. Then no jumper is required. :thumbsup:


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## nolabama (Oct 3, 2007)

John Valdes said:


> The motors are connected with three wires, so it is safe to say motor temperature was not considered.
> However, he is using Baldor Super "E" motors. They come stock with thermal overloads. I guess they are not connecting them.
> *Dorian*. Right? You leave the two leads marked P1 and P2 disconnected when you replace a motor?


Do the VFD's have a termal overload in them?
I mean like a breaker does. I am asking cause I dont know. Not to help with the troubleshooting


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## lefleuron (May 22, 2010)

A drive will more then likely have a self temperature monitor, this will keep an eye on the heat sink temp inside the VFD case itself.

Then you have a motor temp, which is just what it sounds like. The P leads out of the motor are run to terminals on the VFD, and if they open you get a motor over temp fault.

Most VFDs you can program the motor temp fault out, but I have not found one that you could program out the VFD heat sink temp sensor.


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## JRaef (Mar 23, 2009)

nolabama said:


> Do the VFD's have a termal overload in them?
> I mean like a breaker does. I am asking cause I dont know. Not to help with the troubleshooting


Let's get the terminologies correct here.

Yes, a modern VFD that is UL listed will have a motor thermal overload protection feature built-in, so you do not need a Thermal Over Load relay external to the VFD (as long as you are controlling only one motor with it). 

In ADDITION to the motor TOL protection, many VFDs also include a separate Thermistor Monitoring Circuit that can be connected to a set of thermistors that might be embedded inside of the motor. The temperature at which the thermistor changes its resistance value is selected to happen at just below the thermal damage curve of the motor insulation. Thermistors are resistors that change resistance rapidly with temperature. If the motor was not built with thermistors inside already, you can't really add them in the field (although they can be added during a rewind). So for the VFDs that provide this feature, it is usually defeat able in programming. If not, you can always install a jumper wire between the input terminals for it. 

Then in ADDITION to those protections, drives have thermal over temperature protection FOR THEMSELVES, which has nothing to do with the motor. You need to understand that because sometimes VFDs use similar terms for all three functions yet they mean different things in terms of troubleshooting. 

For example, many Asian drives with a cheap simple LED display will give you a fault code of something like "OL 1", "OL 2", or "OL 3" where 1 means motor TOL, 2 means thermister OT, or 3 means the VFD is too hot. You need to know the differences.


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## JRaef (Mar 23, 2009)

> Also could this be caused from the wrong motor data input when they swaped out the motor, and didn't match the RPM's and ratings exactly with the original motor parameters ?


To address this specific issue, yes absolutely! If the VFD is using SVC (Sensorless Vector Control), then the motor parameters are stored and used by the VFD so that it can do the proper excitation of the windings to get peak performance out of it. If you install a different motor, the VFD should have been reconfigured for that motor. Most will provide an Autotune feature to do this, but you have to tell it to perform that and it is done with the motor uncoupled from the load. If that didn't take place, the output of the VFD is likely saturating that motor and heating it up.

in older VFDs that did not have SVC, this would not be an issue and maybe whomever swapped out that motor was used to that not being a big deal, but if the VFD is less than 5 or 6 years old, chances are that it is an SVC drive.


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## John Valdes (May 17, 2007)

JRaef said:


> So for the VFDs that provide this feature, it is usually defeat able in programming. If not, you can always install a jumper wire between the input terminals for it.


I have always found a resistor or resistors mimicking the correct resistance in regard to safe temperature is required and not a jumper on controls with this capability. This would/should cause a fault alone, as the absent resistance of the jumper will indicate an external problem in the temp monitoring circuit. (Temperature loop).




JRaef said:


> To address this specific issue, yes absolutely! If the VFD is using SVC (Sensorless Vector Control), then the motor parameters are stored and used by the VFD so that it can do the proper excitation of the windings to get peak performance out of it. If you install a different motor, the VFD should have been reconfigured for that motor. Most will provide an Autotune feature to do this, but you have to tell it to perform that and it is done with the motor uncoupled from the load. If that didn't take place, the output of the VFD is likely saturating that motor and heating it up.
> 
> in older VFDs that did not have SVC, this would not be an issue and maybe whomever swapped out that motor was used to that not being a big deal, but if the VFD is less than 5 or 6 years old, chances are that it is an SVC drive.


The drive uses a parameter "Motor Poles". Entering the correct motor poles is/should be sufficient for proper operation.
However. In the "motor data" parameters you can set the actual slip RPM.
He is using 4 pole motors and this parameter was set to 4 pole. I see no issue here.

You may want to check deeper as I am going from past experience, and I do not know this drive. He is using a Siemens Micromaster 440 control and I have no idea how old or new these controls are.


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## dronai (Apr 11, 2011)

John Valdes said:


> I do not know this drive. He is using a Siemens Micromaster 440 control and I have no idea how old or new these controls are.





The whole system is only 2 years old.

Wasn't able to get more info yet on the timer issue, until next tuesday.


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## JRaef (Mar 23, 2009)

John Valdes said:


> I have always found a resistor or resistors mimicking the correct resistance in regard to safe temperature is required and not a jumper on controls with this capability. This would/should cause a fault alone, as the absent resistance of the jumper will indicate an external problem in the temp monitoring circuit. (Temperature loop).
> 
> 
> 
> ...





> ...and didn't match the RPM's and ratings exactly with the original motor parameters


Sorry, I interpreted that (maybe over interpreted) to mean a different number of poles, you seem to know he just meant a different slip.

The MM440 is an SVC drive out of the box. The "number of poles" parameter is mainly for the display function. The motor parameters I am referring to are the above-and-beyond stuff that you didn'ty used to have to think aboput before SVC. Here is some of what the MM440 needs to know about the motor:

P1910 = 1:
All motor data and inverter characteristic will be identified and parameter will be changed.
- P0350 stator resistance,
- P0354 rotor resistance,
- P0356 stator leakage inductance,
- P0358 rotor leakage inductance,
- P0360 main inductance
- P1825 on-state voltage of IGBTs
- P1828 compensation time of gating unit interlock
P1910 = 3:
Saturation curve will be identified and parameter will be changed.
- P0362 ... P0365 magnetizing curve flux 1 .. 4​- P0366 ... P0369 magnetizing curve imag 1 .. 4

Again, it will gather this information FROM the motor in an Autotune procedure, but if that was not done when the motor changed, then there is a risk that the output of the drive is heating up the new motor.


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## dronai (Apr 11, 2011)

JRaef said:


> Sorry, I interpreted that (maybe over interpreted) to mean a different number of poles, you seem to know he just meant a different slip.
> 
> The MM440 is an SVC drive out of the box. The "number of poles" parameter is mainly for the display function. The motor parameters I am referring to are the above-and-beyond stuff that you didn'ty used to have to think aboput before SVC. Here is some of what the MM440 needs to know about the motor:
> 
> ...


 
Thanks JRaef, We found that the HMI on the VFD's cannot be changed.
The changes have to be made in the Scada/PLC system from the control rm. We are in the process of hiring a Siemans S7 PLC Engineer, that will make any modifications to our system.

I do know the Techs are changing out motors from our stock, without exact matches.


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## John Valdes (May 17, 2007)

dronai said:


> I do know the Techs are changing out motors from our stock, without exact matches.


Then auto tune each motor to the drive when you switch it out. Check the manual to see if the motor must be uncoupled from the load during any of the auto tune tests.

I have not looked, but there should also be a parameter group for motor nameplate values. This will be in addition to the list above.


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## dronai (Apr 11, 2011)

John Valdes said:


> Then auto tune each motor to the drive when you switch it out. Check the manual to see if the motor must be uncoupled from the load during any of the auto tune tests.
> 
> I have not looked, but there should also be a parameter group for motor nameplate values. This will be in addition to the list above.


Thanks John, According to the other electrician, he tried to modify the settings, and the PLC overrides any changes. I'll look into it.


Also just found out that the timer to the VFD's is internal from the PLC. I have to trace out the wires from the aux block ((or another timer) that they are bypassing, to see where they are going, and why that would be causing a problem. 

I was told by bypassing the Aux, they were able to limit the number of VFD faults ??


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## John Valdes (May 17, 2007)

dronai said:


> I was told by bypassing the Aux, they were able to limit the number of VFD faults ??


That's because the contactor ahead of the VFD was a mistake IMO and they were having issues (tripping) with toggling of the VFD input power.
Jumping out circuits to appease the maintenance staff is short sighted and should be highly discouraged. Should this contactor be the cause of nuisance tripping, a remedy is in order, not a jumper.


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## JRaef (Mar 23, 2009)

John Valdes said:


> That's because the contactor ahead of the VFD was a mistake IMO and they were having issues (tripping) with toggling of the VFD input power.
> Jumping out circuits to appease the maintenance staff is short sighted and should be highly discouraged. Should this contactor be the cause of nuisance tripping, a remedy is in order, not a jumper.


I couldn't agree more.


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## nolabama (Oct 3, 2007)

JRaef said:


> I couldn't agree more.


Me three.


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