Powerflex 70 Break Frequency/Voltage/? on PMAC

blystovski

Member
Join Date
May 2011
Location
Ohio
Posts
4
I have a Powerflex 70 that recently fried in a power outage. The drive is connected to two permanent magnet AC motors via two contactor/overload sets to allow the two parts of the machine to be synchronized for operation. I installed a new drive, and got it working - but only after setting the "break frequency" parameters to the maximum frequency (136 Hz) and voltage (400) listed on the nameplate (and programmed into the appropriate parameters).

The initial symptoms were that the motors together were causing the drive to fault on high current. Running only one or the other (both identical) caused the drive to go into current limiting, and eventually the associated overload would trip.

Trending the frequency, voltage, current, torque current, flux current, and power factor lead me to believe that something was going south at the break frequency, and that the motor was ultimately slipping poles. I tried to increase the break voltage, and the starting voltage, but it seemed to have little effect.

So I am asking here, before I ask Rockwell in the morning - does anyone have any ideas what could be going on? My only hypothesis at the moment is that the voltage is not the only thing that happens at the "break frequency" - perhaps the PWM frequency changes? Really not sure where else to go - symptoms seem to indicate that the motor would almost immediately lose torque at the break frequency, and it would start "slipping" poles not long after, resulting in low power factor and high current.

Thanks in advance for any help!
 

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