GE AF-600 FP Design Manual page 157

Derating of output current versus altitude at T
7.6.5 Derating for Running at Low Speed
When a motor is connected to a frequency converter, it is necessary to check that the cooling of the motor is adequate.
The level of heating depends on the load on the motor, as well as the operating speed and time.
7
Variable (Quadratic) torque applications (VT)
In VT applications such as centrifugal pumps and fans, where the torque is proportional to the square of the speed and the power is proportional to the cube of
the speed, there is no need for additional cooling or de-rating of the motor.
In the graphs shown below, the typical VT curve is below the maximum torque with de-rating and maximum torque with forced cooling at all speeds.
Legend: ─ ─ ─ ─Typical torque at VT load ─•─•─•─Max torque with forced cooling ‒‒‒‒‒Max torque
Note 1) Over-syncronous speed operation will result in the available motor torque decreasing inversely proportional with the increase in speed. This must
be considered during the design phase to avoid over-loading of the motor.
156
for frame sizes 4x, 5x and 6x.
AMB, MAX
Maximum load for a standard motor at 40 °C driven by an AF-600 FP drive
AF-600 FP Design Guide