SIEMENS
2/17
Siemens MD 50.8 · 2017
Configuring guide
Configuring a motor for inverter operation
2
■
Operation of geared motors on a frequency inverter
It is possible in principle to operate geared motors on a
frequency inverter.
Please note the following supplementary conditions:
•
Maximum speed of the geared motor
in the field-weakening range
•
Maximum speed of the brake, see
page 6/32
•
Speed limits of the backstop
■
Motor characteristic
During the acceleration process, frequency inverters shift the
speed-torque characteristic of the three-phase asynchronous
motor over the traversing range to enable jerk-free acceleration.
This enables the motor to be operated at different speeds
(e.g. rapid traverse/creep speed), but also protects the
mechanical components of the plant and gearbox.
Two main motor operating ranges are applicable for inverter
operation:
Constant flux (constant torque)
For frequency inverters with an unregulated DC link
(e.g. SINAMICS G110M), the output voltage can be as high as
the line-side input voltage minus any voltage drops in the
inverter (for example, for SINAMICS G110M:
U
Output
= 0.87 x U
Input
).
If the maximum output voltage has not yet been achieved, the in-
verter output voltage can be increased as the motor speed in-
creases until
V/f = constant
applies. As a consequence, the
magnetic flux, the motor current and therefore the transferred
continuous torque are constant
(provided that the motor is ad-
equately cooled –> in the case of self-cooling, the torque must
be reduced in accordance with the motor characteristic at low
speeds due to the reduced cooling). Alternatively, if a separately
driven fan is used, the full motor torque can be utilized.
Field-weakening range
If the speed increases further when the maximum output voltage
has been reached, V/f
remains constant. The magnetic flux
reduces with increasing motor speed, the motor current and
therefore the transferred continuous torque reduces with respect
to 1/n, and the breakdown torque reduces according to 1/n
2
(see motor characteristic). The motor can be operated in the
field-weakening range at constant power as far as the limit of
stability (see under "Mechanical stress, grease service life").
Fig. 2/11
Example for a 4-pole, three-phase asynchronous motor
Fig. 2/12
Torque-speed characteristic for asynchronous motor
(based on the example of LA63ME4)
■
Utilization in accordance with temperature class F
For rated power and line operation, the motor is utilized in
accordance with temperature class B (130 °C maximum permis-
sible constant temperature referred to a maximum cooling air
temperature of 40 °C).
Siemens motors are designed as standard to temperature
class F (155 °C maximum permissible constant temperature
referred to a maximum cooling air temperature of 40 °C).
For inverter operation at reduced output voltage, the power
reserve of the motor can be used to achieve the rated power.
In this case, the rated torque is applied to the motor and the
frequency inverter outputs a frequency at which the motor
achieves rated speed.
At this operating point the slip and current input are higher than
under line operation, so that the constant motor temperature
increases accordingly. Prerequisite for utilization of the motor in
accordance with temperature class F is that the frequency in-
verter is capable of outputting a sufficiently high level of current:
I
FUoutRated
I
Motor Rated Inc
Fig. 2/13
Drive characteristic for various inverter frequencies
T
rated
T
3
2
1
1.5
2.5
0.5
n
2
1
~
T
bk
n
rpm
n
rated
f
=
f
s rated
f
= 75 Hz
Constant flux
Field-weakening range
G_D087_EN_00263
f
= 50 Hz
f
= 30 Hz
0
2500
2000
1500
1000
500
n
rpm
G_D087_EN_00264
V
/
f
= const. -> I
= const. (Y circuit)
V
/
f
= const. -> I
= const. (D circuit)
Field-weakening range
(Y circuit)
Field-weakening range
(D circuit)
T
Nm
1.80
1.60
1.40
1.20
1.00
0.80
0.60
0.40
0.20
0.00
Limit of stability 50 Hz
S1 torque external cooling 50 Hz
Breakdown torque 50 Hz
S1 torque self-cooling 50 Hz
Limit of stability 87 Hz
S1 torque external cooling 87 Hz
Breakdown torque 87 Hz
S1 torque self-cooling 87 Hz
4500
4000
3500
3000
2500
2000
1500
1000
500
0
Const. flow range
Field-weakening range
Use acc. to
temperature class F
Use acc. to
temperature class B
With separately
driven fan
T/T
rated
G_M015_EN_00216
100
90
80
70
60
0
0
10
50
70
Hz
f
%
20
30
40
60
80
100
© Siemens AG 2017