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Inclined Ropeway, Torque Follower, Choppers Buring Out


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#1 Omer

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Posted 25 January 2008 - 09:24 PM


Hello!
Recently I came to know of an application designed for an inclined ropeway. The application is using two 450 HP motors (and drives) to control the speed on the inclinded rope way. The rope-way is being used to carry lime-stone from a mountain to the factory in the valley. The drives are connected to a single gear box which is in turn connected to the rope-pulley.

The vendor (AB) has suggested to use one drive in speed control and the other drive as a torque follower. My first question is simple -

1. how can you configure a drive as a torque follower?

2ndly, I have tried running the system on a single drive. The drive (AB Impact series) has a chopper circuit with a 2.5 ohm braking resistor. Problem is that IGBTs keep frying out. This means that the resistor is too small for the chopper cuircut. Is this assumption correct?

3rdly, Why not use just one drive on this application. I have read a couple of other emails on this forum that address a curshing application in which two drives are being used. Why are two drives and motors used on a single shaft? Why not just use one bigger motor?

Thanks in advance for your help.

Clear skies
Omer





#2 marke

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Posted 27 January 2008 - 02:50 AM

Hello Omer

1. The aim of using a torque follower is to share the load.
If you use one as the master, and take the torque output from that and apply the torque output from the master to the slave, the slave will try to run at the same torque. The actual method in doing this are dependent on the actual drives being used, so you need to find out how from your supplier.

2. The resistor value determines the maximum braking torque. The resistor KW rating is dependent on the total energy that needs to be dissipated.
If the resistance of the resistor is too low, it will damage the brake chopper. The supplier or the manual will tell you the minimum resistance for the model in question.

3. Often, it comes down to economics. It can be cheaper to use tow smaller systems in parallel. In the case of soft starting, the start current is lower if you soft on one motor and switch the second motor on line when the crusher is up to speed.

Best regards,





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