Changing to AC motor


Thread Starter


Hello this is Perihan,
We are producers of extruders for cable sector. Now we use dc motor and drive, but we want to use ac motor and driver. This machine is required stable low speed. Therefore we will select ac motor with feedback and forced ventilation. Other side I wonder about the values. So that I use motor power 23kw and 1500rpm and 154nm as dc motor. What must be ac motor power? Again 23kw is enough or must be high. Which parameters are important? I check power and torque and speed. What other parameters? for example power factor (cos ).

Could you help me
electronic engineer
mrs =F6zkan
e-mail : [email protected]
One thing is to know more about the peak torque of the application. The power data you have is continuous ratings. It says nothing about the peak
torque delivered by the dc motor - drive system. As you probably know, some types of extruders have high breakaway/overload torque requirement. In any case, you need the ac motor - drive system to generate same continuous power and peak torque (and velocity). Maybe one easy way to tell is by the nameplate data. The max. dc drive current compared to the motor's continuous current will tell you the overload (peak) factor.
as a general rule of thumb you can increase the size of the motor by one size which gives you a close torque match.i have done what you want to do on a mallifer extruder,we used an abb drive running in dtc mode and with no feed back of motor speed.this proved very accurate even at one or two screw rev's and was consistant thru material types,but remember torque is the important number.
cheers lee
You don't mention what country you hail from, but you might consider calling in your local ABB representative, and consult with them on the sizing.

I haven't used one of their DTC (Direct Torque Control) AC drives with an extruder yet (plan to), but have used one in a different application, and was pleased with the results. You'll want to look around, and check out other manufacturers as well, but ABB's DTC has a couple of design twists that make it look (at least, on paper) a better choice than a simple V/Hz
inverter, or 'regular' flux vector drive for extrusion. Depending on the required speed regulation you may even find that encoder feedback is optional. Couple it up with a forced ventilated inverter duty AC motor that can produce full torque down to the lowest speed you'll need it at. You might be able to get by with a 10:1 motor (also called a 6 to 60 Hz motor,
at least in America), but probably want full torque at slower speeds, so would need a more expensive motor with a wider full torque speed range.

To assist in selection, measure armature DC amps and voltage (and field amps, if field weakened) during a start-up, and throughout the normal speed
range while loaded, and calculate and plot the actual KW. Also calculate the percentage of armature amps vs. nameplate full load amps. This will give you a good idea whether to oversize the drive and motor or not.