vfd app. 1

[puckman31]

Are there many problems using a vfd on a 460v 1 hp inverter duty motor that uses a slipring ?. Are there some concerns with this design ?. A good part of the work by motor is at 60 hz

 

[jraef]

If you already have a wound rotor motor it is inherently capable of variable speed (really torque) control without a VFD. Some people don't like the WR control system and choose to replace it with a VFD. If that is what you are doing, then you must fully study and understand the torque / current relationships to the rotor resistance circuit. When you short the rotor to use it on a VFD, you end up with a squirrel cage induction motor that has very low starting torque with very high starting current. A good sensorless vector VFD can overcome some of these issues, a cheap one probably cannot. You should also short the rotor ON the rotor, not on the brush side to avoid added complications with the VFD as the brushes wear. That means disassembling the motor, shorting the rings, rebalancing it and reassembling it. On a 1 HP motor, it's likely cheaper to just swap it out.

Also examine your need for variable speed. If it is for enery savings, running most of the time at full speed from a VFD will actually INCERASE your energy consumption because the VFD has losses.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376

 

[puckman31]

the slip ring i used is a rotating electric connection to a 460v motor. I can not explain this any better and hope most people know what i mean. thank you for you patience.

 

[jraef]

Ah, you mean you are supplying the motor via a slip ring on a moving structure? Different animal if that's the case.

The issue there is going to be with any possible discontinuity of the slip ring power source, but most drives store a small amount of energy storage in the capacitors to be able to ride through any reasonable anomalies. Over sizing the drive might help a bit but I wouldn't get too excited about it. I've done VFDs on Whirley Cranes and on rail powered cranes, never had a problem.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376

 

[LionelHutz]

Are the slip rings before the VFD or after the VFD?

 

[PersonalProfile]

This may be of interest:

http://www.eng-tips.com/viewthread.cfm?qid=317132

Regards,
Lyle