Powerflex 753 Motor Overload Setting

[spark-e-eng]

I have recently replaced a AB 1336 VFD with an AB Powerflex 753 drive and now have the drive faulting on motor overload (Fault code 7). Prior to replacing the drive, they had no operational issues. Everything has been checked mechanically for any issues that could be causing the overload and none were found. According to the manual the overloads are set based on the nameplate FLA and service factor (1.00 SF, 60HP 71.2A for inverter duty, 75HP 87A for Sine wave duty). I know that the NEC has a provision for increasing the motor overloads to 130% in certain applications for 1.00 service factor motors, but how do we set that in the drive since we are just giving the drive the FLA? I watched the amp output on the drive and it gets up to about 87A at about 45Hz and keeps backing off until it eventually faults on OL. I spoke with drive technical support and they were not very supportive.

Any ideas on how to increase the overload setting to 130% to maintain compliance with NEC, yet allowing us to run? I should also mention that this drive is on a mixer and is located about 150-200ft from the motor.

 

[weressl]

I have recently replaced a AB 1336 VFD with an AB Powerflex 753 drive and now have the drive faulting on motor overload (Fault code 7). Prior to replacing the drive, they had no operational issues. Everything has been checked mechanically for any issues that could be causing the overload and none were found. According to the manual the overloads are set based on the nameplate FLA and service factor (1.00 SF, 60HP 71.2A for inverter duty, 75HP 87A for Sine wave duty). I know that the NEC has a provision for increasing the motor overloads to 130% in certain applications for 1.00 service factor motors, but how do we set that in the drive since we are just giving the drive the FLA? I watched the amp output on the drive and it gets up to about 87A at about 45Hz and keeps backing off until it eventually faults on OL. I spoke with drive technical support and they were not very supportive.

Any ideas on how to increase the overload setting to 130% to maintain compliance with NEC, yet allowing us to run? I should also mention that this drive is on a mixer and is located about 150-200ft from the motor.

There is a host of other parameters that may cause the OL condition. Do you have the settings from the previous drive? Did you crosschecked them with the new drive? What type load is it, constant or variable torque? What is the V/Hz slope characteristic? Slip correction? Torque boost? Is the drive proerly identified the motor pre-stratup? Cable lenght? Grounded system or resistance grounded? Etc, etc, etc....

 

[spark-e-eng]

I don't have the settings from the old drive, electricians put it in the dumpster before I knew about it and our documentation wasn't the best for this one. This is a mixer so I think it is considered constant torque. Drive is set for sensorless vector control, torque boost, slip correction all default (and is typically the case for our drives), static autotune was ran on the motor, distribution system is on a high resistance ground, cable length about 150-200ft. Since the drive is faulting on motor overload I would think only the settings related to motor overload would be relevant. If the cable length were an issue now it should have been before too.

Does setting the motor overload factor to 1.30 (130% FLA) maintain compliance with NEC?

 

[petersonra]

I have recently replaced a AB 1336 VFD with an AB Powerflex 753 drive and now have the drive faulting on motor overload (Fault code 7). Prior to replacing the drive, they had no operational issues. Everything has been checked mechanically for any issues that could be causing the overload and none were found. According to the manual the overloads are set based on the nameplate FLA and service factor (1.00 SF, 60HP 71.2A for inverter duty, 75HP 87A for Sine wave duty). I know that the NEC has a provision for increasing the motor overloads to 130% in certain applications for 1.00 service factor motors, but how do we set that in the drive since we are just giving the drive the FLA? I watched the amp output on the drive and it gets up to about 87A at about 45Hz and keeps backing off until it eventually faults on OL. I spoke with drive technical support and they were not very supportive.

Any ideas on how to increase the overload setting to 130% to maintain compliance with NEC, yet allowing us to run? I should also mention that this drive is on a mixer and is located about 150-200ft from the motor.

if it is taking 85A at 45Hz, perhaps the motor is just undersized. maybe they never ran the other drive at this speed.

by the way, what do you mean by "keeps backing off"?

Have you tried running the motor at 60 Hz line power to see what kind of current it takes?

 

[spark-e-eng]

The other drive was ran at the same speed setpoint and it did not have overload issues that resulted in a fault and I don't suspect it was due to some unusual drive setting. We set up our drives pretty much the same every time and don't take advantage of most of the settings. I believe there is a setting in the drive that is causing this in order to prevent full overload but if I turned it off I think it would just fault sooner.

When I say it backs off I mean that it drops to about 36Hz (@73A) for about 40 seconds and then goes back to 45Hz (the setpoint @87A). This happens about 7 times and then eventually the motor overload fault occurs.

We have never tried to run the motor at full speed but i would guess that it would require more current and would trip on overload sooner.

 

[weressl]

I don't have the settings from the old drive, electricians put it in the dumpster before I knew about it and our documentation wasn't the best for this one. This is a mixer so I think it is considered constant torque. Drive is set for sensorless vector control, torque boost, slip correction all default (and is typically the case for our drives), static autotune was ran on the motor, distribution system is on a high resistance ground, cable length about 150-200ft. Since the drive is faulting on motor overload I would think only the settings related to motor overload would be relevant. If the cable length were an issue now it should have been before too.

Does setting the motor overload factor to 1.30 (130% FLA) maintain compliance with NEC?

A mixer(agitator, centrifugal load) would be a variable torque load, not constant.

See page 120 on the power jumper configuration for non-solidly grounded system. (Harmonic content raises w. ungrounded HRG systems and may be falsely interpreted as OC.)