Motor Runs 150% Speed

1.- Electro-micro-erosion can quickly wear out the bearings.

2.- Current pikes at the carrier frequency (from 2 to 16 Khz depending on the drive and settings), can damage the winding insulation, resulting in premature failures.

You will have to perform periodic inspection and maintenance as recommended by the motor manufacturer (and you will be the first one I know of doing so).

Yahlasit

I could be wrong here, but if he is running a 6-pole motor at 75hz, the chances are his motor would be fitted with a certain bearing size specific to the frame-size, whatever the number of poles. So mechanically, the motor would be designed to operate at least up to 3600rpm (2-pole 60hz speed). Now if he was running a 2-pole motor at 75hz, that would be a different matter, although I've come across some motor manufacturers that will rate their motors to 5000rpm.

The real answer is; none of us can answer you definitively, you MUST get your answer from the motor manufacturer. Bearings are a big issue in this, as is cooling. Some cooling designs are such that an increase in speed may actually DECREASE the cooling capability. Only the specific motor mfr. can address these issues.

All that said, a motor creates torque based on it's V/Hz ratio. To maintain a constant torque you must maintain that ratio. If your motor is designed for 400V at 50Hz, that is a V/Hz ratio of 8:1. If you increase the Hz to 75 and you cannot increase the voltage correspondingly, then you are DECREASING the torque capability of the motor because you have lowered the V/Hz ratio to 5.333:1 or 2/3 of what it was. Unless your load torque requirement decreases to 2/3 of what it was at 50Hz, you will likely stall the motor, but you will at the very least increase the load on it. If your cooling is diminished and the motor is overloaded, the result is the loss of the motor.

If however your motor can be strapped for 240V so it has a 4.8:1 V/Hz ratio and you are using a 400V supply, then you can set up your VFD to put out 360V at 75Hz and you will have the proper V/Hz ratio. But make sure you size the VFD for the 240V current rating of the motor if you want to do this.

so here is a generic problem...so none would consider going into details...i would simply advise the first reply that is: a time to time bearing check-up and make some efforts to have your motor replaced or employ VFD's...