Siemens SINAMICS PERFECT HARMONY GH180, Function Manual

Page: 198 / 538

maximum motor inertia listed in Appendix NEMA Table. You may enter a known value of
maximum motor inertia. Obtain this value from the manufacturer.
Straight inverse time
Choose "straight inverse time" protection if the motor has an allowable current level of 100% e.g.
when the motor is equipped with a constant-speed cooling fan.
Inverse time with speed derating
Choose "inverse time with speed derating" when the motor is not equipped with an external
blower. With this option the allowable current level is determined from the speed derating
curve.
Note
Importance of speed derating
The motor has no external blower, and is cooled only by the rotor mounted internal fan, which
decreases in efficiency with speed. This could lead to overheating of the motor and lack of
protection.
Enter the allowable motor load curve values for various speed breakpoints via the keypad. The
default derating curve provides breakpoints for a quadratic cooling curve.
6SHHG
0
D[
0
RW
RU
/R
DG
Figure 7-11 Default speed derating curve showing maximum motor load as function of speed
The motor manufacturer normally provides data for the curve. The control software uses the
allowable current level to determine the cooling capability of the motor.
If you prefer to enter a fixed value of an allowable current level other than 100%, as with the
"straight inverse time" option, you can modify the speed derating curve to have the same desired
level for all breakpoints.
Operating the Control
7.7 Motor Thermal Overload Protection
Control Manual
196
Operating Manual, A5E50491925A