change Wound rotor motor to VFD fed induction motor
change Wound rotor motor to VFD fed induction motor
(OP)
There are existing 1600HP wound rotor motors driving centrifugal pumps at a water pumping station. There is a push to convert the motor to a VFD driven induction motor.
The VFD cost is high. The thought is that reliability would be improved. Also maintenance on the slip rings would go away.
I was wondering if anybody has data on reliability for a VFD-induction motor compared to a wound rotor motor? Is converting a wound rotor motor to inductor motor worth the cost?
Thanks for the input.
The VFD cost is high. The thought is that reliability would be improved. Also maintenance on the slip rings would go away.
I was wondering if anybody has data on reliability for a VFD-induction motor compared to a wound rotor motor? Is converting a wound rotor motor to inductor motor worth the cost?
Thanks for the input.





RE: change Wound rotor motor to VFD fed induction motor
The voltage stresses on the motor windings might be a concern, but the old motors could run a long time on a new VFD.
RE: change Wound rotor motor to VFD fed induction motor
thanks.
RE: change Wound rotor motor to VFD fed induction motor
One can also make an argument that VFD controls will save a little extra energy as well.
But here we go... 3...2...1... launch objections to that last statement!
RE: change Wound rotor motor to VFD fed induction motor
The VFDs are getting pretty reliable - but 1600 hp is a big drive. Is this a 4000 V motor?
I agree with jraef that most installations where money is a big issue stick with the rheostats or resistors until the thing just falls apart or they can't make them work anymore.
RE: change Wound rotor motor to VFD fed induction motor
Some of the sliprings I worked on as an apprentice had a hand switch to short out the rings once up to speed thus reducing wear on the brushes. I wonder if it's possible to get a solid state device to do that.
I agree with Jraef, liquid starters are cool!
Roy
RE: change Wound rotor motor to VFD fed induction motor
I should have qualified that savings issue a bit more, dpc is absolutely correct. If you are running at full speed all or almost all of the time, a VFD will actually cost you MORE than a sorted WR controller.
RE: change Wound rotor motor to VFD fed induction motor
If the calculations on ROI are done with the choice to use a BFD on the application, it may be viable to investigate some level of output filter between VFD and motor if the insulation is suspect or simply rewind (yeah, 'simply'!) the motor to higher insulation class. Do your ROI calcualtions on each scenario, including just replacing the motors.
RE: change Wound rotor motor to VFD fed induction motor
RE: change Wound rotor motor to VFD fed induction motor
RE: change Wound rotor motor to VFD fed induction motor
Do you have reliability problems now? What are they? Big drives bring their own maintenance requirements: the cooling fans and their filters, especially in a dusty or dirty environment, are a maintenance overhead; electrolytic capacitors are a relatively short lifetime item; a large unit may require auxiliary cooling plant.
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RE: change Wound rotor motor to VFD fed induction motor