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nvrsrinivas
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Join Date: Sep 2013
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AC Equivalant Motor for 500 KW DC Motor

07/24/2018 12:13 PM

We want to replace our 500KW DC motor for our kiln in our cement plant with AC motor and VFD. I request you to kindly enlighten me how to calculate equivalent AC motor for 500 KW DC motor.Since this motor is for cement kiln,it needs very high starting torque. Please help me. Thanks,

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RAMConsult
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#1

Re: AC equivalant motor for 500KW DC motor

07/24/2018 12:47 PM

Your best bet is to contact manufacturers of Variable Speed AC Motor/Drives. They are in the best position to recommend a package solution that will satisfy all your needs (none of which have you provided to the forum).

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Brave Sir Robin
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#2

Re: AC equivalant motor for 500KW DC motor

07/24/2018 12:51 PM

In general, this sort of thing is not a catalog buy, plug-and-play solution. You will need to hire a company or consultant to help you choose the right motor and drive to meet all your requirements of which we know little. Doing this on your own is a huge risk.

With an Internet search, you may also find providers who supply both the motor and drive. That should be your first stop on this journey.

You should start here:

https://www.globalspec.com/productfinder/motion_controls/motors

https://www.globalspec.com/productfinder/motion_controls/controls_drives

JRaef is an excellent source of good information on motors and drives. Until he chimes in, I will offer this:

For a motor to be able to provide high torque under slow speed operation you will need a motor with vector feedback and a controller that is compatible with the slow speed operation.

rwilliams also has direct experience with cement plant kilns and may be able to direct you to an appropriate source and may be even willing to consult for you for an appropriate fee.
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rwilliams
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#4
In reply to #2

Re: AC equivalant motor for 500KW DC motor

07/24/2018 1:43 PM

The reduction ratio (for at least paper mill calciners, lime kilns) is so high, typically the motors are equivalent mechanical designs. The dc motor is a shunt wound, with standard series compensation. AC motors on kilns have been applied since the mid 1990s, even before the advent of our newer and more accurate vector control models. I do see that the breakdown torque capability of a typical ac vector controlled motor is somewhat less than an equivalent dc motor when starting, (assuming easy to get NEMA Design B ac motor), so it is common practice to increase the frame size of the drive motor (larger rotor diameter), so that the breakdown torque is equivalent, without going to a specially engineered product. This is as much a drive technology conversion as motor conversion.

That said, look back through the mechanical requirements for the original kiln, and check to make sure the breakdown torque of your actual drive motor rating is maintained, during the time rating. And/or look back in motor load trend history, and see if you an find a restart after a power outage while in production. The kiln will sag between the supports if stopped while hot. The drive motor must be capable of getting the kiln turning again with a sagging shell and the load at the bottom, especially in the case where the inching drive start was delayed.

IEEE has published many papers on the subject, you might find some reassurance reading the following that Cimintec has republished, starting on Page 7...

http://www.cimentec.com/uploads/reports/KILN_DRIVE_APPLICATION_CONSIDERATIONS_IAS_Article.pdf
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SolarEagle
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#3

Re: AC equivalant motor for 500KW DC motor

07/24/2018 12:57 PM

These guys might be able to help....

https://www.sentridge.com/services/dc-to-ac/

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lyn
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#5

Re: AC Equivalant Motor for 500 KW DC Motor

07/24/2018 4:22 PM

Maybe here? It covers the subject nicely.

AC Replacement for DC Mill-Duty Motors - TMEIC
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daveoliver
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#6

Re: AC Equivalant Motor for 500 KW DC Motor

09/17/2018 9:45 AM

You haven't given enough information for an accurate answer. When retrofitting a DC system to Ac there is a 150% increase in the AC motor and drive rule of thumb to compensate fr the torque loss using a standard 4 pole motor. You can use a 6 pole motor but will sacrifice the top rated speed.

Very High starting torque is not definitive enough. Do you know the inertia that will have to be overcome?

I can assist if you can provide the motor data from the nameplate

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