Replacing DC Motors with AC Motors

I hvnt used so large dc motor. I think how do you replace, one is dc, another is ac?

you hve to construct another ac line at first and then select a same speed, this is important. I thiink,and then a same power rate or a bit little power, as the ac motor has more effeciency than dc motor.

im also waiting for more detail and more right answer.

By changing over from DC to AC, the motor rating will not get affected.Your load demands it.Hence the rating will be same 247 kW.

Standard rating is 255 kW for a four pole motor ( Max speed 1780 rpm for 60 Hz supply).Slight reduction in speed should not be of concern.

Frame size may be larger: 355 or there about in metric size.

Regards

Cowlagi

Keep the speed, KW and torque same for ac mpotor as well. It can be replaced.

shivaram

I assume you are looking at also a VSD to drive the motor. And if so, I would be looking at Closed Loop Vector drive to give good torque control. Things to watch are torque requirements of you load for start through to full speed, DC in the past had better torque at the low speed and starting speed, but Vector VSD now are capable of full motor torque at zero speed.

If this application is just to run at 1850 rpm, again look at the load and starting torque reqirements, then look at different methods of motor starters.

Rregards,

Trevor

Hello Rao,

Be very careful in what you are trying to do..

I was in a similar situation sometime back. I remember I argued with the sales engineer of a famous brand of motor who tried to sell me a 20hp AC motor to replace 20hp DC motor.

After many hours of arguments and calculations finally it worked out to the point that I needed a 30hp+ AC motor to replace the 20hp DC motor.

On the face of it as others say if you maintain power & torque it should work.

Remember DC motors are known to have very high starting torques and normally run at low speeds.

As this incident happened about 15 years back I cannot remember the exact arguments but I still remember the final results- The engineer could not sell his AC motor to me but he became a very good friend of mine for life!

Be very careful and analyse starting torque, speed etc..that is my advice

I have done such conversions many a times succesfully but for smaller sizes of motors i.e 30 kw,from DC to AC (Induc. motors)and the same should apply for the bigger motors.

to convert Dc motor to AC you need to upgrade the AC motor to 25-30 % i.e 247 KW DC motorm can be replaced with an AC induction motoe of 320 KW .Ac induction motors have lower starting torque compared to DC motors and the bigger size compensates for the same.

Bear in mind the AC motor should be of the same RPM or you could use a AC motor drive .

Appropriate AC motor starting and protections,cables, should be fitted which will be suitable for the AC motor.Discard all the Dc motor switch gears and leads.

Finnaly remember the Pully or sproket if attached to the AC motor should have the same O/D as was of the DC motor to maintain the M/C rpm.

Good luck,