Current Drawn By A Motor When Starting Via A Variable Frequency Drive

• "The best one could achieve would be 2 to 3 times the full load current. One cannot go lesser than this."

This statement is true for Reduced Voltage Solid State Soft Starters, but not for VFDs.

Because a VFD is controlling both the voltage AND the frequency (unlike a RVSS that controls the voltage only), you can in theory get a motor to produce full torque at any speed, and if you use a Vector Control VFD, that is absolutely true. Given that then, you can accelerate a motor with no more than 100% of motor rated current.

HOWEVER, what will change is the amount of time. If there is a lot of inertia, 100% of motor rated current may take you 1, 5, 10 or 15 minutes to fully accelerate it, or if you want to accelerate it in 10 seconds, you might have to allow the VFD to go to Breakdown Torque output, which means upward of 250% current. So without knowing the required acceleration parameters you are looking for, you cannot make any accurate prediction of motor starting current when using a VFD.

But to answer your SPECIFIC question, theoretically you can accelerate a motor with 100% of motor nameplate FLC if you use a VFD, as long as you do not care how long it takes to get there. And because you are not exceeding the FLC of the motor, you can take 3 weeks if you want to...

Additional information can be found in the manual for the VFD/VSD depending on how it is set and what motor load you are trying to drive.