VFD Question

This is not a problem, but you must plug in new motor values into drive program. otherwise the vfd will over drive your motor.

>What if I connect the 25 HP Siemens MM440 drive with 20 HP motor?
 
B
two parameters must be specified seperately for changing motor to a VFD drive.

1. V/F ration i.e. flux density in the motor. Check the motor nameplate for voltage/frequency value, motors may be 440V or 415V or 400V with same frequency 50Hz in India. for this v/F ration slightly differs.

2. Max allowable current. i.e. motor full load current. In your case it will be less.
 
As a general rule, you can connect any motor to a drive that is SMALLER than the drive rating, and if you know what you are doing, even LARGER than the drive rating as long as you don't expect full power).

But many, if not most, drives that are capable of Vector Control will have a lower limit on the size, because for Vector Control to function, the VFD needs very precise motor current information. So at about 50% of the VFD rating, the motor current at low speeds becomes too low for the sensors to remain accurate enough. So you will likely see in the MM440 manual that you cannot use that drive on a motor smaller than 10HP.

If however you are using it in V/Hz mode (no Vector control), you can use that drive on any motor smaller than 20HP. Ive used a 20HP drive on a 1HP motor before.
 
Top