is it possible to run 1.25MW/660V motor(presently run by vvvf drive), directly by applying 660V to stator or just by passing the whole drive unit.
Is there anything like softstarter for this purpose?

 

If your system allows you can start this motor directly on line or by using a soft starter..
VVVF drives are best suited as the starting current are the lowest compared to any other type of starting (except rotor resistance starters which obviously need a slip ring motor).
Check with your overload trip settings for your main 660 v distribution system and the system capability before trying a soft starter or DOL.
Hope this helps,
Sekar

 

if it is a standard motor there should be no problems running fixed speed. You should talk to the motor supplier.

There are several options relating to a soft starter for the motor, again talk to the supplier.

 

Responding to Sandy's Sep 11 query:

The Rule-of-Thumb (darn, did it again) capacity of the power supply, up to the point of connection of the motor, should be five to six times the motor's hp rating. In this case the motor is about 1,500 hp. Thus, required system capacity should be about 7,500 kVA. Under this condition minimum voltage will be about 550 to 600 Volts, corresponding to starting current magnitudes of 5 to 6 kA (rms), respectively.

However, a major concern is the minimum torque developed by the motor to accelerate the load within a specified time. The time limit is imposed
so as to not overheat the rotor during runup. Stator overheating is also a concern, but, to a lesser degree (please excuse the pun).

Regards,
Phil Corso, PE
(Boca Raton, FL)