Created Date: December 30,2002

Created by: DAVID WAGNER

DUSTY,

PUT THE DRIVE ON HIGH SPEED WINDINGS AND RAMP DOWN TO THE SLOW SPEED RANGE OR PUT IT ON THE LOW SPEED WINDINGS AND RUN OVER 60HZ FOR THE FAST SPEED. IF THE MILL IS A LARGE INERTIA LOAD, A VFD MAY HAVE PROBLEMS WITH STARTING THE LOAD. ACROSS THE LINE MOTOR STARTING GENERATES A LOT OF HP. A SLOW RAMP WITH A VECTOR DRIVE USUALLLY WORKS FOR THIS.

Created Date: December 30,2002

Created by: Tom Jenkins

A couple of points should be mentioned. On a constant torque load, like a conveyor or a positive displacement pump, the VFD is usually one size larger than the VFD for the same hp motor on a variable torque load like a fan or a centrifugal pump. This allows it to put out full amperage across the speed range. Look closely at the VFD specs to make sure it is rated for the type of load you have.

Second, if you run above 60 Hz with most VFDs you are limited to constant horsepower. That means that you have to make sure the motor and VFD will both handle the torque required by the load at the highest output frequency you will be using.

Finally, if your two speed motor was 2:1 speed ratio, and you get a motor for the higher nominal speed, check the cooling at the lower speed. Many TEFC motors get into heating problems below 50% of nominal speed, particluarly on constant torque loads.

I agree with David that this is probably a good application for a VFD - just make sure you do thorough engineering of the motor and drive and load as a system.

Created Date: January 06,2003

Created by: Carl@ADCsupport

All the drives that ADC sell are rated as constant torque.

I prefer not to use dual speed motors; especially vintage. In the long term, it is usually cheaper to replace both.

If the motor is vintage and you can't replace it; then I also suggest line reactors on both sides of the drive.

Check out the faq's as well:

http://support.automationdirect.com/faq/showfaq.phtml?id=816 http://support.automationdirect.com/faq/showfaq.phtml?id=774 http://support.automationdirect.com/faq/showfaq.phtml?id=855 http://support.automationdirect.com/faq/showfaq.phtml?id=295 http://support.automationdirect.com/faq/showfaq.phtml?id=747

Created Date: January 07,2003

Created by: Daniel Williams

What is the system voltage? If it is 480 AND the motor is not "inverter " rated, you will end up replacing it or having it rewound after a few years use.

We have several motors in our plant from Europe that are not inverter rated. The run time varies from motor to motor but the average is running about 2-3 years of actual run time on the windings before they fail.

A load side reactor can extend the life of the windings but there are other stresses that an inverter motor faces that the standard across the line motor does not.

You do not have to change the motor out. BUT if this machine is critical to your production, you had better have a spare motor on the shelf.

Created Date: January 16,2003

Created by: dusty

Thanks all for your thoughts - as a result I 've gone with a rotary phase converter and step up transformers to get the 3 phase 380 volt power into the milling machine. The machine is sort of a "swiss watch " type machine so I want to run it for awhile as designed. The other problem with the inverter approach is that some of the accessories plug into the machine's 380 volt socket and are then controlled by the other controls. Dusty