Powerflex 525 loses speed control when nearing 60hz

So I'm running into a strange problem with a new Powerflex that was installed on an existing conveyor.

When the commanded frequency approaches 60hz (seemingly anything above ~57hz) the drive will lose its ability to control the motor speed. The motor frequency will be shown as nearing 64hz and lowering the reference speed will not slow down the speed frequency shown. The drive will show "Decelerating" and after a seemingly random period of time (30s to a few minutes) the motor will usually slow back down to the new reference speed.

Some background info; Motor - 5 HP 600V, Drive - 5 HP Powerflex 525.
The VFD that was replaced was an old 1336, can't confirm if the motor behaved the same on the old drive as the conveyor never ran above ~50hz previously. Tried all kinds of configurations on the new drive, disabled voltage regulation, changed carrier frequencies, replaced the drive. Have not replaced the motor yet. It definitely has to be something with the motor or the leads but the customer is refusing to believe its the motor and I'd like to figure out whats actually happening.

Rockwell tech support is stumped, my office is stumped, anybody ever seen something so strange?

Thanks

Check the following:
P039: Torque Performance Mode. The default is SVC, make sure someone didn't set it for Economize. Economize will automatically lower the V/Hz ratio in the assumption that the load is Variable Torque so you need less torque if the current demand drops under a given speed. If the load is CT, like a conveyor, and the load drops because of some loading issue or begins overhauling, the drive "lets go" of the motor and allows it to spin as it will. You never want to use Economize on a CT load that might overhaul.

Check A495, Drive OL Mode. This tells the drive how you want it to react to an overload condition before it trips. The choices are Disabled, Reduce the Current Limit, Reduce the PWM (Carrier Frequency) or Both, which is the factory default. What Current Limit will do is to reduce the Hz output, overriding the speed command; Reducing the PWM (lowering the Carrier Frequency) reduces the torque without reducing the speed; Both means it does both simultaneously. When set to Both, if the OL condition ceases, the drive will return to the commanded speed and increase the CF, but the return to the speed command takes place at the Accel rate, vs the return to CF (and thus torque) returns instantly. So if the OL condition goes away quickly, the increased torque may cause the motor speed to increase above what the drive is telling it to run at (because the return to commanded speed has an accel rate). If P039 is set for SVC, the speed display is the actual motor speed, not the commanded speed, because in SVC, the drive is actually tracking rotor speed. So if you don't know that, you might think the drive is acting funny, but if you look at the commanded speed (b002) you will see that it doesn't agree with actual motor speed (b001). Then if the motor is over speeding, the drive will attempt to slow it back down (your Decelerating display), but again, AT the decel rate. If you don't want this to happen in your application, you can disable A495, so long as everyone understands the consequences. You can also play with your accel and decel rates.

Check A441, Droop Hz. This reduces the Hz when the load approaches the set FLA. Unless you have two drives on one load, you shouldn't be using this, again especially on a load that might overhaul.

What is the motor load my guess is that it's near 100% or more
the commanded speed is 57hz but the drive runs at 64hz it looks like it's a vector drive. they look at the counter EMF of the moor to determine the actual motor speed and adjust the output hz to get the motor to run at the desired speed. I have seen this many times I had one the customer kept complaining about the difference between the set point and output Hz the default set was to display the output hz. (most are) I just changed the display to show the set point hz customer was happy nothing changed on the drive or out put speed.
as for the deceleration time check the dec. setting of the drive my guess is that it is set to a very long time 120 sec or so or you have an over-hauling load on the conveyor ( Material pushing the conveyor faster then the drive set-point)

jraef,
The drive was reset to defaults many times. SVC was the setting used. V/Hz was also tried. Drive OL is set to Both. The motor is not running anywhere near an OL condition. This happens even with the motor disconnected from the load. The decel rate is having no effect as the rotor feedback will stay stuck at ~64hz for random lengths of time before eventually ramping down to the new speed command. When the motor is stuck at that speed the current draw is around 4.5 amps, drive is rated at 6.6, motor rating is 5.5 amps.

Gary,
Motor load is about 70% when the runaway occurs. The ramp times are set to default at 10 seconds.


It's as if the the drive is being confused by the back EMF readings somehow and not knowing the rotor speed.
If I was to set the reference speed to 59hz and start the drive, it will get to 59hz and hold that speed properly. If I then command a lower speed such as 40hz, the drive speed will actually runaway and increase to ~64hz, hold there for a random amount of time (all the while showing decelerating) then eventually get to the 40hz that was commanded. No PID settings are being used.

Hw are you setting the drive speed?
You said that it a conveyor could it be a networked communication of some kind.
check that the communication is not delayed for some reason. You may enter a speed change but if there is a delay in the transmission to the drive then this will happen.

It happens even when using the pot on the drive.

The difference between the set point hz and the output hz is the nature of a voltage vector drive. They look at the counter EMF to maintain the motor speed (RPM ) at the desired speed.
The deceleration thing is another thing overhauling load would be the first thing I would look at.
I would also check the drive setup it may be set to coast to stop deceleration.
in that case the speed would depend on the load and how fast it can slow down.
Look at the speed reference compared to the output speed. if the reference is changing to the lower value but the output speed is taking a while to make the change.
Most drives by default display the output speed so cost to stop would show the actual speed.
Be careful when you change to controlled ramp deceleration if the load is overhauling the drive may trip on an Buss Over Voltage Fault.

Make sure your minimum Frequency is not greater than your maximum frequency. The min frequency should be between parameter 80 and 85, I can't remember where the max frequency is. But if you have already reset it to default settings, then this may not be the solution, but worth a try.

After 5 years I got the same fault.
When hits the 60hz the VFD freezes and you can not even stop it.
I changed the decel time (P042) to 2 seconds and it works.
If you want you can go back to your costumer ����