VFD Motor to Replace Wound rotor Motor

[GusD]

We have one conveyor that is currently powered by 5 -1250 hp WRM.4 motors driving 2 pulleys at the head end, and 1 motor at the tail drive.The length of the conveyor determines the # of drives needed to move a certain load.
Soon we will be increasing the Tonneage on this conveyor and it appears that we need a 1500 hp at the tail instaid of a 1250 hp.In addition to wanting to use a 1500 hp induction motor (not WRM) we would like to put a VFD to power the 1500 hp.
We realize that we will have to try and syncronize the VFD at the tail with the WRMs at the Headend.Perhaps there will be other problems that we have not foreseen.
What problems can we expect form this arrangement.
I am not refering necessarily to the possible inherent problems with VFDs.More so on the combination of these 2 not so similar motors.

Thank you


GusD

 

[jbartos]

Suggestion: The system synthesis will be of the high priority. Namely, motor torque-speed curves need to be properly integrated, the speed of conveyor belt sensed and used for the motor controls, boundary conditions set, and possible optimization of the integrated system for the conveyor varying load implemented.

 

[DougMSOE]

For this arrangement you need to define the master motor and the slave motor(s). The dispatching of these motors may have to come from a plc that will as jbartos stated compare the speed torque curves. My suggestion is to measure the torques of each motor and have the plc do the calcs.
The last time I did an up-grade like this, we used DC motors and it worked out very well.

 

[mdonner]

Make sure your new motor can operate at the required control range (1:250 ?), at constant torque.
If your existing WRM controller has analog torque output (4-20mA or 0-10V), the new VSD should run in torque control mode (with upper speed limit for protection), using that analog signal as input. Otherwise load-sharing has to be controlled using PLC and transducers.

 

[GusD]

Hello and thanks for trying to help.

JBartos= As you mention the Speed/Torque curve matching would be all important.We use PLCs and Encoders on all our systems,it might take some work, but we should be able to do it.We are now going through the RA or DAnalyses.Even if we pursue this expensive option,we are still a long ways from detailed Eng.We do have other options.The cheaper option would be to add another WRM to the tail drive.We have a few of those around.Shortening the belt from 2.5Km to 1.5 Km and use another shorter conveyor.We have all the parts needed if we go this route.
To DougMSOE= as JBtos info you are right.As for the Master/Slave relationships,we do have the stepping of the Drives timed in such a way that the 2 TOP drives in the Head Station are picked up 2 steps ahead of the 2 Lower drives and the tail drive.Somebody told me one day, that it had to do with the coefficient of friction.I didn't argue.

Mdonner=Just as MSOE and JBtos you are all looking at the same sheet of music and makes a lot of sense.
Thank you again for the help.

Note.To anyone using WRMotors and monitoring their speed with Encoders or Tachos.We have on some of our Rotor systems, neat little devices like HullEffect CTs.Instead of a current output they give a Freq. output from 0 to 10 volts.This is just like a CT and just as robust as a CT.If you want to monitor the Speed of the WRM this might be the cheapest and reliable way to do it.

Regardingguys are normally call it or wound rotor stage for Speed monitoring characteristic


GusD

 

[Farkel]

My concern would be with torque issues, since each step of the wound rotor motor has a different characteristic, and speed change, and how one would coordinate these parameters.