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System Manual – MOVIDRIVE® compact Drive Inverters
4
Motor selection for asynchronous AC motors (VFC)
Project Planning
4.4
Motor selection for asynchronous AC motors (VFC)
Basic recommen-
dations
•
Only use motors with at least thermal class F.
•
Use TF thermistors or TH winding thermostats. TH should be preferred for group
drives on one inverter. The series connection of the TH contacts (normally closed) is
not subject to limitation when both monitoring functions are used.
•
For group drives, we recommend that the motors should not differ from one another
by more than 3 motor types.
•
Use 4-pole motors if possible. This recommendation applies particularly to gearmo-
tors operated with a high oil filling level due to their vertical mounting position.
•
Generally speaking, the motor can be operated at its listed power without forced
cooling if the operating conditions differ from S1 operation, e.g. positioning drive with
1:20 speed range in S3 operation.
•
Do not select a motor that is too big, particularly for delta connection. Otherwise, the
inverter may trigger a short circuit fault.
•
A MOVIDRIVE
®
compact
MCV4_A or MCH4_A drive inverter is required for speed
control. In this case, the motor must be equipped with an incremental encoder, pref-
erably with 1024 increments/revolution or with a Hiperface encoder.
Voltage/fre-
quency charac-
teristic curve
The VFC operating mode runs the asynchronous motor on a load-dependent
voltage/frequency curve. The continuous calculation of the motor model enables the full
motor torque to be utilized right down to the lowest speeds. This characteristic curve is
set by entering the rated motor voltage and the rated motor frequency in the startup
function. The setting determines the speed-dependent torque and power characteristics
of the asynchronous motor.
The following figure shows an example of the voltage/frequency characteristic curve of
an asynchronous AC motor 230/400 V, 50 Hz.
1 Star connection; 400 V, 50 Hz
2 Delta connection: 230 V, 50 Hz
3 Delta connection: 400 V, 87 Hz
The inverter output voltage V
out
is limited by the connected supply voltage. The "rated
supply voltage" input value in the startup function limits the effective value of the maxi-
mum output voltage. This restriction is used whenever the connected motor has a lower
rated voltage than the power supply of the inverter. Enter the maximum permitted motor
voltage. Furthermore, make sure that the "rated supply voltage" input value is less than
or equal to the supply voltage of the inverter.
01650BEN
Figure 58: Voltage/frequency characteristics of the asynchronous motor
0
230
400
0
f [Hz]
50
87
1
3
2
V
outp
[V]
Summary of Contents for MOVIDRIVE compact MCH41A
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