Drive/motor question (1336 impact)

[jouellet]

Hi Guys,

here is the setup:

application is crane. We have a 1336 Impact drive, with a 30 HP motor w/encoder and a dynamic braking system.

attach to that, is a little Micrologix, that only monitor the actual speed vs the commanded speed, and if the difference is greater that a certain preset, for 'x' amount of time, the Micrologix disable the drive. the drive will then immediatly activate the mecanical holding brake, that now acts as an emergency brake

normally, when the load is going down, we can see that the dynamic braking is working, and the load stops with no problem.

lately, the Micrologix keeps on disabling the drive, because the motor does'nt seem to brake in a timely manner

braking resistor/chopper has been proven good.

we called tech support, and they told us that the motor had probably changed its internal specification. we were told to try to do an Autotune on it. We tried the autotune, but it failed on the Flux test.

We then raise the current to 100 % rather than 50 % (as mentionned in the manual) same thing happened, we failed again on an "Hi Flux" fault.

we called tech support again, and based on those new information, we were told that the motor must be "dying slowly". I've never personnaly seen a motor "dying slowly" !!!

we then decided to place another 30 HP motor and try to do an autotune ( we don't have an exact replacement on hand...)

we entered the new motor's data, and tried the autotune. the Flux test that was failing before, started, but it lasted forever (I mean more than 30 minutes !!!) and never completed.

Tech support again, but this time, the guys was more confused then us !He wanted us to abort the autotune, and to enter the flux data manually, from the manufacturer's recommendation ! We wanted to prove that the drive was OK, not that we can run another motor ....

We went back on the crane, and one of the electrician did put his foot on the motor's shaft (that was still trying to do an autotune..) the motor then speeded-up/slowed down a few time, then told us that the autotune had completed !!!

WE are now all confused: can I assume that the drive is OK ? (I think so) can we blame the motor ? (my guess is Yes)

anyone ever experienced something similar ? any ideas ?

Tks

Jasmin

 

[robertmee]

I've had similar issues with 1336 Impact and Force drives, but it's been 10 years or more since I messed with them. They were always very particular in the Autotune test. I've seen many motors that would operate on a standard VFD fail on the Impact drives. They are very sensitive to any insulation breakdown in the windings which is what is happening with a 'slowly dying' motor.

 

[OkiePC]

My experience with the Impact is also about ten years old. Make sure you follow exact proceudres when autotuning, and before you begin, be prepared to revert to known working values if it fails.

I had an application with an oddball motor that could not be autotuned and required manual settings to be used, and customized for each antique motor on our machines.

A/B autotuning cannot always work, and can often fail for reasons that should point your right at the cause of your problem.

Once tuned, it should work fine even with reasonable wear and tear on the mechanical system and even motor replacement with a motor of the same design. This is not always true with very hotly tuned systems or oddball motors, or unreasonable mechanical changes.

I would bet there is a problem external to the tuning values, but if you are sure the chopper circuit is working (verify DC bus volts and current through resistors), then you'll want to ensure that the drive is responsive to decel commands (no sticky relays or gains too low), and if you find that it is not, look into increasing the responsiveness by manually tweaking the pertinent parameters. Been too long for me to guess at which ones of the several hundred parameters available might help.

Good luck,
Paul

 

[OkiePC]

Look at User Manual/AC Drive FRN 1-4.XX 1336EUser Manual1336 IMPACT-5.0-APR02

Chapter nine discusses applications and choosing a braking method, and shows how to set paramter 76 to regulate the maximum allowed regeneration.

Chapter 12-21 discusses the Bus Voltage tracker and how it interacts with regeneration and precharge.

Also investigate the parameters for Pos Torque Lim (parameter 74) and Neg Torque Lim (parameter 75). I remember our application (without external chopper) requiring different values in these from default in order to perform to our requirements during deceleration under widley varying loads.

It is also possible to use Data Links to attach a fault/status bit to determine when current is being limited and why...I had to use that feature to figure out why sometimes my current was being limited so I knew which of the 296 parameters to look for!

 

[DickDV]

It could very well be that the motor is changing slightly as tech service states which makes the motor nameplate data you entered years ago slightly invalid.

It's a lot of work but you could change the drive to v/Hz mode and load the motor to its nameplate torque at 60hz and actually measure slip. Use that actual number for nameplate speed (sync speed - slip). Then change back to vector mode and do the retune.

It seems that the slip value is especially critical in building a proper motor model and nameplate is not necessarily correct, even on a new motor. This problem gets worse, percentage wise, on modern motors because the slip value is getting so small. An error of 2 or 3 rpm is getting to be a rather large percentage of the actual value.

 

[jouellet]

Solution found

Hi Guys,

motor testing showed that it was just fine !

Encoder was "dying slowly", as would have said the A-B's tech support.

When I called then previously, I asked about the encoder; they told me not to worry about the encoder, because if it was missing a pulse, or not working properly, the drive would know it right away, and give us an alarm...

That's "Bull s..." after more that 8-9 different combinations of autotune, we finally got a "SpdFBLoss" alarm.... we then dismantled the encoder to find out the is was in a very bad shape: when doing a 360 rotation, it was stiff half of the time.

inside the encoder, the "slotted" wheel was almost all ripped apart. No way that this encoder was sending proper pulses !

Conclusion: if the drive behave strangely, blame the encoder before the motor, even if the drive says the opposite !

Thanks for your help/ideas !

Jasmin