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Topics: Variable frequency drive parameters on AC Drives
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08-14-2012 10:56 AM

Variable frequency drive parameters

I want to know that is there any parameter in variable frequency drive that limits the current during acceleration?

According to my calculations it can be possible with ideally 50% speed. Practically 15HP motor can provide the same torque but just approx at 45% speed.

I want to know is there any way to replace a 30HP motor from 15HP motor?
08-14-2012 10:57 AM
Top #2
08-14-2012 10:57 AM
Most of variable frequency drive have a parameter which limits the motor current. However, you need to keep in mind another things. The motor torque is not the same in all the speed range. The 30HP motor could develop 45HP at the start moment if doesn't have a VFD or even 60HP, if it has one. Besides that, how about the physical dimensions like the shaft height?
08-14-2012 10:59 AM
Top #3
08-14-2012 10:59 AM
Thanks for your reply,
I have 22.5KW motor installed with LS VFD. The motor takes 20 to 26A current during acceleration. The acceleration time is 15 Seconds.
Suppose that, i limit the current to 15A, than variable frequency drive shows overcurrent alarm and than trip.
I need such setting that VFD continue to run even it can not be able to reach full speed.
Manually it can be configure by setting Hz and User Defined V/F characteristics, but is it possible that VFD perform the same action by itself.
According to my information,
low speed require less current to achieve desired torque

I have prepared this presentation and mention my query in last slide.
08-14-2012 11:00 AM
Top #4
08-14-2012 11:00 AM
According to my views, the rotating magnetic field of stator catches the rotor more strongly if its speed is low and to vary its stator magnetic field variable frequency drive is designed.
So using VFD, we can get the more torque at low speed. This is what i want to say.
I have a ball mill running with 30HP motor. The product inside the ball mill is the paste of chocolate that need high starting torque for sometime. I realized that, during acceleration, it takes approx 30A current at 380V, and after completing its acceleration period i.e 15 seconds, the motor takes 20A current only.
By calculation the motor need to deliver 30HP at start than settled down to 20HP at full speed.
So, i want to know that, if i install 15HP motor here and compromise on speed of motor, to achieve desired torque, than what is the parameter i need to adjust, i.e
1. Limit output current of VFD to 15A. (due to 15HP motor)

1. Allow variable frequency drive to accelerate.

In this condition the VFD normally tripped due to over current, but i need to run VFD at this limited current regardless of speed.
Speed is not an issue in this case.
What is the parameter i need to use for this case?
I am currently working on Parameter Stall Prevention Level as per Ignacio Waldman said.
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