adccommunitymod (AutomationDirect) asked a question.
Slip Ring/VFD
Created Date: October 25,2007
Created By: sii
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I am trying to convince my boss (and his boss) that converting one of our machines from variable speed DC to three-phase AC motors is a good idea. Does anyone have experience running motor leads from a VFD through a slip-ring. If so, were there any unexpected problems that you encountered? The voltage would be 480.
Created Date: November 12,2007
Created by: RogerR
I have ran equipment with VFD drives supplying 460v 3PH motors through slip rings for years.
If you set up a new project, make sure that the slip rings are rated for AC voltage and higher voltage as the case may be. Many DC motors are either 90V or 180V armatures and the original slip rings may be rated for this.
Make sure that the slip rings have a redundant ground. If one ground in the slip ring fails even in only one spot, then the second one will protect personnel in the event of a short circuit.
The plus side is that there are no brush problems after this kind of upgrade and the motors are much cheaper.
One down side is that if one phase is lost through the slip rings even for brief periods of time, then the motor single phases.
If the field of a DC motor is lost through the slip rings, the same is true for the DC motor. Many times it draws high amps.
All things considered, my perference is to never put in a DC motor in any installation when rebuilding equipment.
Created Date: October 25,2007
Created by: sii
I am trying to convince my boss (and his boss) that converting one of our machines from variable speed DC to three-phase AC motors is a good idea. Does anyone have experience running motor leads from a VFD through a slip-ring. If so, were there any unexpected problems that you encountered? The voltage would be 480.