High speed setting range at constant power (field weakening operation or field control range)

For specialized drive jobs, like coiler drives, test rigs, winders and unwinders, etc., very large setting ranges at constant power
are stipulated. In these cases, conventional field weakening operation with an externally excited DC machine makes
implementation particularly cost-efficient. This means: the larger the speed range in which a motor can output its maximum
power (length of the horizontal section of the characteristic in Fig. 5, from nG
 to n
1
), the smaller the overdimensioning factor
can be kept Pmax(motor)
/ Pmax(load)
.
Values obtained from empirical feedback:
A typical value for the field weakening range of DC Motors
with a shaft height of 112 ... 225 mm in the rating category of
5 ... 360 kW (M ≤ 2900 Nm) is 1 : 3.
The maximum value for the field weakening range at compensated DC motors with a shaft height of ≥ 250 mm in the
rating category of 125 ... 1400 kW (M = 2400 ... 24500 Nm)
is 1 : 5.
Example: compensated DC Motor DMA + 280 K (see Fig. 5)
nG
n
1
nmax
Speed n (rpm) 0 500 1500 2500
Power P (kW) 0 130 130 80
Torque (Nm) 2483 2483 827 305
Values obtained from empirical feedback:
Due to the pull-out torque  Mk
 ≈  MN
  x  2,5, the  typical value
for the field weakening range is only 1 : 1.5 up to a maximum
of 1 : 2.5 for all standard AC Motors.
Example: AC Standard Motor ...450LL12 (see Fig. 5)
nG
nmax
Speed n (rpm) 0 500 1250
Power P (kW) 0 130 130
Torque (Nm) 2483 2483 933