Permissible Motor-Converter Combinations - Siemens SINAMICS G130 Engineering Manual

Drive Dimensioning
Engineering Information
In the field-weakening range, the motor current I
asynchronous motors for any field-weakening point according to the following formula:
Key to formula:
·
f
·
f
rated
·
I
μ
·
M
·
M
rated
·
I
Act-rated
Stall torque M
k
M V P
Torque limit curve
for forced-cooled motors
Torque limit curve
M
for self-cooled motors
rated
V
rated
P
rated
M = f(n)
V = f(n)
or
P = f(n)
Constant flux range
0
0
Typical characteristic of thermally permissible torques in continuous operation of Siemens asynchronous
motors as a function of speed when motor is utilized according to temperature class 155 (F)
10.4

Permissible motor-converter combinations

Rated motor current higher than the rated current of the converter or Motor Module
If the motor used has a higher rated current than the rated current of the converter or Motor Module, the following
must be noted.
The motor cannot be operated according to its ratings, but only under partial load. The higher the rated current of the
motor as compared to the rated current of the converter, the lower the possible partial load. Another factor to
consider is that the power factor cosφ of the motor becomes increasingly poor as the load on the motor decreases. In
a borderline situation, the motor can only be operated on its magnetizing current which means that it cannot be
loaded at all. This borderline situation is encountered with typical asynchronous motors in the power range of about
100 kW if the ratio between motor rated current and converter rated current reaches approximately 3:1.
SINAMICS Engineering Manual – November 2015
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Ó Siemens AG
2
æ
æ ö
f
ç ç
= ç ç ÷ ÷ × +
2
I rated I
m
Mot
f
è ø
è
Motor frequency at the field-weakening point under consideration
Rated frequency of motor
Magnetization current (no-load current) of motor. This is calculated from the rated current
I of the motor and the rated power factor cosφ
Mot-rated
.
= - j
I I 1 cos
m - -
Mot rated Mot rated
Motor torque at the field-weakening point under consideration
Rated motor torque
Rated active current of motor. This is calculated from the rated current I
motor and the magnetization current I
.
= 2 - 2
I I I
m
Act - rated Mot - rated
in line operation
Stall torque in converter-fed operation
M M =
rated
M = M
rated •
Nominal
Operating point
Field-weakening range
f n
or
rated
rated
can be calculated with acceptable accuracy for typical
Mot
2 2
ö æ ö
f M
÷ ÷ ç ç ÷ ÷
× ×
2
I
-
Act rated
f M
ø è ø
rated rated
of the motor as follows
μ
in the field-weakening range
( ) 2
f
rated
M = M
•
k-reduced k
f
V V =
rated
or
P P = Voltage V
rated
or
Power P
Difference ≥ 30%
f
rated
f
Operating point in the
field-weakening range
f n
or
.
of the motor as follows
Mot-rated
Mot-rated
of the