Lenze DSD - Manual (Page 314)

11 Drive Dimensioning
11.2 Motor selection
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Lenze · Drive Solution Designer · Manual · DMS 4.2 EN · 12/2013 · TD23
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11.2.3 Dimensioning guidelines and dimensioning information
The application range of a motor is defined by its max. mechanical/electrical limits and the thermal
limits.
• Whereas the mechanical/electrical limits are defined by the max. load values (M, n, U, I), for the
thermal dimensioning the load characteristic as a whole is relevant.
• The thermal model of the motor is based on the continuous characteristic (S1 characteristic).
• The DSD simulates the thermal utilisation by means of an approximate model and presents it
in the characteristic field.
• During longer operation with low field frequencies in the SLVC or VFCplus control mode and in
case of deviations between the actual and optimal motor excitation, the motor may heat up
more.
• Remedy: Dimension the drive with greater reserves.
• During longer operation outside of the indicated S1 characteristic, higher inaccuracies may oc-
cur.
• Remedy: Dimension the drive with greater reserves.
11.2.4 Field weakening for winding drives
The field weakening serves to considerably reduce the rated power of the drive. The greater the field
weakening factor the more reduced the required rated power.
In order to achieve high field weakening factors (for max. motor speeds which are not too high), se-
lect a motor with as low a rated speed as possible. Four-pole standard three-phase AC motors (e.g.
in 29-Hz technology) from size 132 are suitable.
The field weakening reduces the magnetisation of the motor above the rated speed. Hence, if max-
imum voltage is provided, the motor is able to operate at a speed which is significantly above the
rated speed.
The power at the motor shaft remains almost constant up to a field weakening factor of approx.
1 : 1.5 to 1 : 2 (depending on the stalling torque). The power decreases with higher factors.
In practice, asynchronous motors for center winding machines are operated with field weakening
factors of up to 1 : 4, in special cases even up to 1 : 5. Synchronous motors can be operated with a
significantly reduced field weakening factor (max. 1 : 1.5). This can be seen from the motor charac-
teristic.
In DSD a slider is used to adapt the field weakening factor in the motor table. Winders with asyn-
chronous motors have a Lenze setting of k
f
= 2. If the field weakening factor is changed, the torque-
speed requirements (blue characteristic) and the utilisation values are automatically recalculated
and displayed in the table. The optimal motor has been found if the characteristic curve (red char-
acteristic) is not exceeded. Dimensioning strategies ( 208)
• Always select a field weakening factor k
f
which is smaller than the winding ratio q:

Note!
The thermal model for operation at the frequency inverter is derived from the same
model as the one for operation at the servo inverter.
• With regard to the system, therefore there may be deviations depending on the con-
trol type (SC, SLVC, VFCPLUS) that is used.