Drive Dimensioning; Drives With Quadratic Load Torque; Drives With Constant Load Torque - Siemens SINAMICS G130 Engineering Manual

Drive Dimensioning

Drives with quadratic load torque

Drives with a quadratic load torque (M~n
starting torques or high load peaks usually do not occur. It is therefore not necessary to provide a higher overload
capability for the converter.
The following applies to selection of a suitable converter or Motor Module for drives with a quadratic load torque:
The rated current of the converter or Motor Module must be at least as high as the motor current at full torque in the
required load point.
When Siemens standard asynchronous motors are used, these can be loaded with the full rated power even in
converter-fed operation. They are then utilized according to temperature class F.
However, if the motors may only be used according to temperature class B, the motor output must be derated by
10 %. For motor types 1LA8 and 1PQ8 the derating is 15 %.
Selection of suitable motors and converters for a specific application is supported by the SIZER configuration tool.
Constant flux range
With forced ventilation
Typical characteristic of the permissible torque with self-cooled motors
at a rated frequency of 50Hz

Drives with constant load torque

The self-cooled motors cannot produce their full rated torque over the entire speed range in continuous operation.
The continuous permissible torque decreases as the speed decreases because of the reduced cooling effect (see
diagram above).
Depending on the speed range, the torque - and thus the output power - must be derated for self-cooled motors.
In the case of forced-ventilated motors, it is not necessary to reduce the output power, or only by a relatively small
amount, depending on the speed range.
In the case of frequencies above rated frequency f
weakening range. The useful torque drops approximately in proportion to the frequency ratio f
asynchronous motors operating in this range. The output power remains constant.
It must be ensured that there is a sufficient margin of ≥30 % between the required torque and breakdown torque
which decreases in proportion to the ratio (f
The base load current of the converter or Motor Module should be selected at least as high as the motor current at
full torque in the required load point.
2
), such as pumps and fans, require full torque at rated speed. Increased
Field-weakening
range
Utilization to
temperature class F
Utilization to
temperature class B
(50 Hz in the diagram), the motors are driven in the field
rated
2
/f) . This applies particularly in V/f control mode.
rated
SINAMICS Engineering Manual - May 2008
Drive Dimensioning
Engineering Information
/f in case of
rated
313/396
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