Induction motor speed contollers vs Variable Frequency Drives

[kitha]

Hi guys!

I have experience in several occasions installing Induction Motor Speed Controllers, one in a water desalination plant and others in process control environments. I would like to share the experience you guys have and how you rate the unit against Variable Frequency Drives. If anybody is interested in what I am talking about following link will be helpful as it contains details and clips as well.

http://www.magnadrive.com/md_asd/how_it_works.shtml

 

[wired1]

The ASD looks like an eddy current clutch. I had some limited experience with this type of drive on a long conveyor that was driven by two motors. the clutch helped balance the motors to eliminate any surging as they reacted to the varying load. As far as I know, a VFD can handle any control situation that the ASD can, plus they have more capabilies. But I'm not sure how they compare on price. . .

 

[kitha]

Just to add an explanation note:

These drives are called by various names, Induction Motor Drives, Adjustable Speed Drives(ASD), Magnetic Speed drives

 

[jbartos]

Suggestion: The posted link leads to the following video:

http://www.magnadrive.com/about_md/video_intro.shtml

The application show savings in energy, lower maintenance costs, no harmonics and spikes, the same footprint, etc.
This is very impressive.
However, the motor starting was not addressed. If DOL, then the usually mentioned disadvantages of the DOL on the motor stays, on the motor load disadvantages are eliminated because of Magnadrive.
The motor magnetizing branch in the motor electrical equivalent circuit is constantly energized with the motor terminal voltage being meant constant. The means that the motor works at the motor terminal rated voltage and frequency parameters.
The shaft load will vary due to Magnadrive settings and controls. This implies that the motor power factor and efficiency vary according to the shaft load conditions.
The posted video link includes applications with energy savings that are appealing to the customer.
The Magnadrive efficiency, controls, reliability, cost, etc. need to be taken into consideration when comparisons are made with VFDs.

 

[kitha]

The load shaft is isolated from the motor shaft and the load shaft is driven by the magnetic induction. Further you can see all the installation details and comparisions against VFDs in the same website. Because the load shaft is not directly coupled the motor starts at no load.