# Slewing motion issue for Tower Crane



## Peewee0413 (Oct 18, 2012)

The drive guru may anwser this one, but is it dropping because its torque limiting?

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## wildleg (Apr 12, 2009)

hang on slewpy


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## smartatuls (Dec 12, 2017)

Peewee0413 said:


> The drive guru may anwser this one, but is it dropping because its torque limiting?
> 
> Sent from my VS995 using Tapatalk


The Torque limit function is not active and torque is fluctuating between 20 - 60 %.

Please see attached trace image.


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## smartatuls (Dec 12, 2017)




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## JRaef (Mar 23, 2009)

Uh... we can't connect to your C:// drive over internet connections, unless some of us are hackers...

You have a drive AND an Eddy Current Clutch on the SAME motor?


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## JRaef (Mar 23, 2009)

wildleg said:


> hang on slewpy
> 
> 
> https://www.youtube.com/watch?v=zoZ5JL3gmHo


Wow, haven't heard that one in years...


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## paulengr (Oct 8, 2017)

In V/Hz mode the drive runs with essentially no feedback so V and Hz by definition is constant barring some other problem. In SVC mode drive estimates torque and speed and runs output accordingly.

Current consists of two vectors. The first about 100% reactive power is the magnetizing field of the motor. The second which is almost pure real power and 90 degrees out of phase to magnetizing current is due entirely to torque developed by the motor.

So if current is erratic then either load torque, something electrical, or the drive sensors has to be going on. If output current is not erratic in V/Hz then we know it’s not a load or power issue...it’s in the torque/speed feedback. So either a setting is out of whack (auto tune it again to recalculate the various motor parameters) or the sensors are bad so buy a new drive.


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## paulengr (Oct 8, 2017)

If current is erratic in V/Hz then test incoming power quality, motor condition, and put a scopemeter on output to look for drive transistors failed, problems with noise, ringing, standing waves, etc. If that looks clean it’s a load issue. In parallel vibration analysis can pinpoint bearings, alignment, soft foot, etc.

We do this all the time. Usually drive problems are easy but not always. If you do go to replace the drive, get rid of the eddy current stuff too to simplify your life and save money. Induction motors are great brakes.


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## smartatuls (Dec 12, 2017)

paulengr said:


> In V/Hz mode the drive runs with essentially no feedback so V and Hz by definition is constant barring some other problem. In SVC mode drive estimates torque and speed and runs output accordingly.
> 
> Current consists of two vectors. The first about 100% reactive power is the magnetizing field of the motor. The second which is almost pure real power and 90 degrees out of phase to magnetizing current is due entirely to torque developed by the motor.
> 
> ...


In V/F also the behavior of current and torque is erratic. We tuned motor several times but no change in problem. I am unable to post image of traces here. I don't see any option to upload image.


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## paulengr (Oct 8, 2017)

If current is erratic in V/Hz mode most likely it’s a load (mechanical) issue. If you take another motor and hook it up without a load or some kind of artificial load or even if you can uncouple it, does it continue? If so, drive is bad. If not it’s a load issue.


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## smartatuls (Dec 12, 2017)

JRaef said:


> Uh... we can't connect to your C:// drive over internet connections, unless some of us are hackers...
> 
> You have a drive AND an Eddy Current Clutch on the SAME motor?


Yes. Both are on same motor.


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## JRaef (Mar 23, 2009)

Then that's the likely source of your instability. The eddy current clutch is reacting to the load, so is the VFD, but both are reacting to the changes created by the other. Both is not a good idea.


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