motor ramping up without command reference

[georgerepard]

i have 1 480v 3/0 motor on a powerflex 525 vfd. it is running a progressive cavity pump. the motor starts to ramp up even when the commanded frequency is at 25hz. the motor will ramp up and down from 25- 60.77 hz and i get an overvoltage fault. i have tested the motor and programmers have checked the plc programming and the system is running as set. i changed the drive out and still same problem. the plc will command the motor off but it continues to run away at 60hz. then the brake locks down and i get a motor stall, of course. so i swapped the motor and everything ran perfectly as commanded to. what could cause this motor to react like this?

 

[petersonra]

If the frequency is changing it is not anything the motor is doing. The VFD has control of what frequency is being fed to the motor so it is the VFD that is the cause.

Why the VFD is doing this is something that may require some investigation on your part.

My guess is the PLC program or the VFD configuration is causing it but it is not real obvious why.

Likely someone has programmed something somewhere that is causing this.

get yourself a copy of CCW from the AB web site.

go thru the setup wizard for the drive INCLUDING resetting the drive parameters to default and going thru the tuning procedure even if you think neither is necessary. trust me, they are absolutely necessary.

where is the drive speed signal coming from? ethernet, MOP, analog input? there are parameters in the drive that you can look at to tell you what these signals are telling the vfd to do.

if you don't have the experience to check it out for yourself best bet is to call AB tech support and ask for help. They are pretty good at figuring these things out, but you need to default the drive and run the tuning sequence first becasue the problem may just go away.

one other thing, PF525 drives are often problematic when run in sensorless vector mode. make sure it is set to V/Hz mode.

 

[Jraef]

drives are often problematic when run in sensorless vector mode.

… Without running an autotune procedure.

 

[TwoBlocked]

i have 1 480v 3/0 motor on a powerflex 525 vfd. it is running a progressive cavity pump. the motor starts to ramp up even when the commanded frequency is at 25hz. the motor will ramp up and down from 25- 60.77 hz and i get an overvoltage fault. i have tested the motor and programmers have checked the plc programming and the system is running as set. i changed the drive out and still same problem. the plc will command the motor off but it continues to run away at 60hz. then the brake locks down and i get a motor stall, of course. so i swapped the motor and everything ran perfectly as commanded to. what could cause this motor to react like this?

Something else changed when you changed the motor. Since it was ramping up and down before, I see this as an intermittent problem (not a steady state one.) Usually that is caused by a loose connection. But since this is a pump application and there could be special parameters used in the VFD for pump applications (such as anti-cavitation, which should NOT be used for a positive displacement pump such as yours) what the VFD "saw" may have caused it to perform erratically.

One thing I wonder, how did you determine that the command signal of 25hz was not changing? A situation like this I like to verify this somehow.

But if it's working now, might best to leave it alone!

 

[petersonra]

… Without running an autotune procedure.

I have found it to be problematic regardless of running the tuning procedure or not. I just don't use it unless I have to and there are very few applications where it makes any difference.

My favorite is it will run fine for months or years and then act up. Running the tuning procedure usually fixes it but so does putting the drive in v/hz mode, and that is a more permanent fix.