joseph_e2
Member
We have a handful of nearly identical flywheel-driven machines. About a year ago, we installed a 15HP Powerflex 525 drive in simple V/Hz mode with DB resistors on one of the machines. It's been running great for that whole time.
We have it set up so the STOP input (terminal 1) is wired through the DB resistor thermostats, input 2 is Run FWD ,and input 3 is Run REV. Since it's replacing an across-the-line reversing starter that's in the midst of a bunch of hard-wired relay logic, the drive's output Relay 1 is Ready/fault and will cause the relays that control drive inputs 2 and 3 to drop if the drive faults. This arrangement has been running fine on machine #1 for over a year.
We tried to duplicate that installation on another machine that has an almost identical motor (np is 1765 RPM instead of 1775, but otherwise the same including NEMA Design) but we're getting DC Bus overvoltage faults after the machine cycles for around 10 minutes. When trending in CCW, I see that the output frequency drops to 0 from one sample to the next while the STOP and Run FWD inputs are still ON and Relay 1 still indicates OK. The commanded frequency doesn't change. On the next sample, Relay 1 drops out, which also drops out input 2 (Run FWD). Then, about 400 ms later, the DC bus climbs past 810V and the drive faults on bus overvoltage. That's the only fault that's shown on the drive. The only parameter differences between the 2 machines are the network addresses and the v7 drive has flying start enabled since it doesn't have a flywheel brake that applies when the motor is stopped.
The first attachment (..._FreqDrop) shows the values of the trended parameters as the output frequency drops. The second attachment (..._NextSample) shows the next trend sample, at which point Relay 1 has dropped, taking Run FWD with it. At this point, the DC bus (the visible graph) is still well within its normal range. It trips at 810VDC, which happens about 400ms after the output frequency drops.
Per a suggestion from Rockwell, switching the drive to SVC (with a static autotune) accelerated the issue and I actually saw the STOP input open when the resistors got hot. The fault happened a lot sooner (in a few minutes of cycling instead of about 10 minutes). They also suggested changing p36 to 1800 to remove slip compensation and then to use P531 to disable the bus regulator, but neither improved the situation.
In case we managed to get a bad drive out of the box (or broke something during installation), we swapped in another brand new drive and got the same result. The only difference between the drive that's working fine and the ones that are faulting is the firmware version. The older one is v6.001 while newer ones are v7.001. The release notes don't highlight any issues. I would rather not flash the firmware down, but that's about my last option that I see here.
Any ideas?
We have it set up so the STOP input (terminal 1) is wired through the DB resistor thermostats, input 2 is Run FWD ,and input 3 is Run REV. Since it's replacing an across-the-line reversing starter that's in the midst of a bunch of hard-wired relay logic, the drive's output Relay 1 is Ready/fault and will cause the relays that control drive inputs 2 and 3 to drop if the drive faults. This arrangement has been running fine on machine #1 for over a year.
We tried to duplicate that installation on another machine that has an almost identical motor (np is 1765 RPM instead of 1775, but otherwise the same including NEMA Design) but we're getting DC Bus overvoltage faults after the machine cycles for around 10 minutes. When trending in CCW, I see that the output frequency drops to 0 from one sample to the next while the STOP and Run FWD inputs are still ON and Relay 1 still indicates OK. The commanded frequency doesn't change. On the next sample, Relay 1 drops out, which also drops out input 2 (Run FWD). Then, about 400 ms later, the DC bus climbs past 810V and the drive faults on bus overvoltage. That's the only fault that's shown on the drive. The only parameter differences between the 2 machines are the network addresses and the v7 drive has flying start enabled since it doesn't have a flywheel brake that applies when the motor is stopped.
The first attachment (..._FreqDrop) shows the values of the trended parameters as the output frequency drops. The second attachment (..._NextSample) shows the next trend sample, at which point Relay 1 has dropped, taking Run FWD with it. At this point, the DC bus (the visible graph) is still well within its normal range. It trips at 810VDC, which happens about 400ms after the output frequency drops.
Per a suggestion from Rockwell, switching the drive to SVC (with a static autotune) accelerated the issue and I actually saw the STOP input open when the resistors got hot. The fault happened a lot sooner (in a few minutes of cycling instead of about 10 minutes). They also suggested changing p36 to 1800 to remove slip compensation and then to use P531 to disable the bus regulator, but neither improved the situation.
In case we managed to get a bad drive out of the box (or broke something during installation), we swapped in another brand new drive and got the same result. The only difference between the drive that's working fine and the ones that are faulting is the firmware version. The older one is v6.001 while newer ones are v7.001. The release notes don't highlight any issues. I would rather not flash the firmware down, but that's about my last option that I see here.
Any ideas?
