Energy saving in VFD driven Induction motor

Quote "I have doubt regarding the exact match between these two motors. I mean, Is the motor replaced correctly ( I guess not because second motor torque will get reduced at 60-65Hz ). end quote

Not necessarily. The drive may be able to maintain the torque at variable speeds.

I would be concerned with the motor running at increased speeds. You need to check

with the manufacturer. If there is a problem with the 66 hz, see if there is a fix for

this motor. The fix may be just replacing the bearings. Also the voltage comes into

question. Take an amp reading on the new motor while running and check it against

the name plate information. Give it to the MFG when you speak with them.

It all depends on the nominal load of the motor. If this motor is running at any percentage below full load then you need to determine if it can cope.

Normally running a 1500 RPM motor above its rated speed will only cause problems if the load is close to the max.

I would suggest calculating the full load in KW and making an educated guess from there.

Dont go 2 pole as the torque will be reduced. If you find you are close to maxing out the design specs you may want to look at a VVVF drive. This may involve upping the size of the motor.

What is the supply voltage to the VFD?

If the output of the VFD can support 66 Hz at 547 volts(ie: support the v/Hz), then your motor is capable of producing 18.5KW * 66/50 = 24.4 Kw.

If the drive can not support the V/Hz of the motor, then the motor will be limited in its capability of producing torque at the 66 Hz. The motor manufacturer would have to tell you its performance at 66 Hz and the peak output voltage of the VFD.