Hi,
It is not inverter motor but a standard derated 105 kW motor. Theoritically it is capable of 132 KW, at what frequency the KW would be 132 kw if this is 4 pole 50 Hz motor ?
The motor can deliver 132kW
at 50Hz. Whether it does depends on the load. And less at other speeds.
How long, the motor could be run at higher than 105 kw ?
The motor thermal limit is 132kW at 50Hz.
Is getting an inverter duty the motor does not need to derate for vfd
I wouldn't normally de-rate a motor for inverter duty. But we usually fit winding and bearing thermistors for protection.
But, as Jraef has noted there are other points you need to take care with.
Bearing currents. Besides earthing (grounding) the shaft, good cabling techniques minimise the potential for bearing currents. Normal practice here (UK) is to use steel wire armoured cable. The capacitance to the armour shunts the currents resulting from the fast switching edges away from the bearings. According to Gambica, good installation practice is is the most important element of achieving good bearing life.
I know of the bearing failure phenomenon but have not experienced it personally and that's after decades in this field. Maybe that attests to the installation and corroborates the Gambica stance.
FWIW, this what it can look like:
Insulation stresses. This is caused by the vary fast switching edges produced by modern PWM inverters. In contrast to the bearing failures, I have seen this all to often. It usually isn't immediate. It's cumulative over a period of maybe a few weeks to a few months eventually leading to a catastrophic insulation failure. One solution that I've used is to fit reactors at the VFD output. Or, as the other guy said, get the right motor in the first place.
Thermal rating. You mentioned that the load is constant torque. If the motor is to run at reduced speeds for significant periods of time cooling could be a problem. Most standard cage motors that I've come across are TEFC (totally enclosed fan cooled). The fan is shaft mounted and the cooling air directed across the cooling fins on the outside of the motor. Reduce the motor shaft speed and you reduce the effective cooling - dramatically. On the last constant torque application we did, we had a separately powered constant speed cooling fan.
Incidentally, the 700Nm is more than 105kW at rated speed.
Apologies for such a long post - I don't usually ramble on this long!