dc motors and drives > replace by ac ones

Kataeb

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Kindly, we have the following dc motors (with their dc drives), running on a rewinding machine, in angular synchronization (small motors following the biggest one, in position control).
The customer requested that the dc motors and dc drives, be replaced by ac motors and ac drives, and to run them in synchronization, like before.

Which power values should we select for the new ac motors?
(we can run the new ac motors upto 60 hz)
Dc Motor1 (master) 82 kw 1780 rpm
Dc Motor2 (follower) 37kw 1498 rpm
Dc Motor3 (follower) 37kw 1498 rpm
Dc Motor4 (follower) 29kw 1630 rpm

Thank you
 
I would use Yaskawa A1000 setup in Flux vector mode.
I have replaced DC drives with then in the past they work well
In this case I would look at using a common buss configuration but I would have to see more details.
 
I would use Yaskawa A1000 setup in Flux vector mode.
I have replaced DC drives with then in the past they work well
In this case I would look at using a common buss configuration but I would have to see more details.

Thank you for your reply.

But, i am looking for some hints, on which motor Kw rating, is good enough for the Ac motors to replace the old Dc ones.
I know that usually we should increase the motor Ac kw by some factor, to be able to do the job of an old Dc motor.
 
It will depend on your available supply voltage. If you use a 480V supply and motors DESIGNED for 460V 60 Hz, 4 pole motors of equal or closest size over those values should be fine. If you use motors designed for 400V 50 Hz but you will operate at 60 Hz without boosting the voltage, then increase the motor kW size by 20% and round up to the nearest standard size.
 
from what you posted
KW is KW dc to ac motor it's the same but if you are concerned select the next standard size up.
as for speed dc and ac motor have a slightly different base speed. All of your motor would be 4 pole motors Base speed at 60hz s 1800 rpm you have to adjust the speed down a little to match the requirements.
here in the states standard supply is 480V 3 phase at 60 Hz other areas it different.

with the Yaskawa I can get them setup to be power directly from your existing 500VDC power source if that's what you need so the conversion is fairly simple. But be aware the motor mounting bases and motor dimensions are not the same so some modifications to the mounts will be required no matter what motor you use my choice in motor would be Marathon I don't know what the availability is where you are. you would have to talk to a local distributor.
 
Which power values should we select for the new ac motors?
(we can run the new ac motors upto 60 hz)
Dc Motor1 (master) 82 kw 1780 rpm
Dc Motor2 (follower) 37kw 1498 rpm
Dc Motor3 (follower) 37kw 1498 rpm
Dc Motor4 (follower) 29kw 1630 rpm

As JREF mentioned, we'd need to know your line voltage and frequency to determine what the output KW of the drive will actually be.

For example:
Motor1, If drive is supplied with 460-480v, a standard 4 pole motor of 82KW will suffice. If drive is supplied with 380v, then you'll need a motor of about 103KW to account for the torque loss above base speed.

Math and Physics can't be changed :D
 
Won't you have to take into consideration that DC motors have more torque at low speeds than AC?
 
Won't you have to take into consideration that DC motors have more torque at low speeds than AC?


Generally, not. Even though a DC motor technically has a higher intermittent torque capability, most often, the drive is set for 150% current limit. In the few applications where they need the torque, it is true, it must be accounted for. In these applications, it's generally safe to consider the Current Limit setting of the existing DC drive (or it's rating x 1.5), and then figure a similar AC drive + motor which will match up, limited to 150% current/torque. For this reason, I normally like to replace a 1800rpm DC motor with a 1200rpm AC motor of the same HP. Assuming, of course, the AC motor is capable of whatever top speed the DC was running.
 
Since wind/unwind applications are among the most difficult to implement and commission properly, I strongly recommend that you find a well-qualified systems group to do this job for you. I can tell from your questions that you are headed straight for a ton of trouble of attempt to do this job yourself.

No insult of any sort intended here, just 30 years of field experience watching what happens when the necessary background and experience is NOT there.
 

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