Optimizing Motor Starting - Siemens SINAMICS G120 Operating Instructions Manual

Advanced commissioning
6.5 Motor control
6.5.1.2

Optimizing motor starting

Setting the voltage boost for U/f control
After selection of the V/f characteristic, no further settings are required in most applications.
In the following circumstances, the motor cannot accelerate to its speed setpoint after it has
been switched on:
● Load moment of inertia too high
● Load torque too large
● Ramp-up time p1120 too short
To improve the starting behavior of the
motor, the V/f characteristic can be
raised at low speeds.
The inverter raises the voltage in ac-
cordance with the starting currents
p1310 ... p1312.
The adjacent diagram shows the result-
ing voltage boost using a linear charac-
teristic as an example.
Requirements
● Set the ramp-up time of the ramp-function generator to a value 1 s (< 1 kW) ... 10 s
(> 10 kW), depending on the power rating of the motor .
● Increase the starting current in steps of ≤ 5 %. Excessively high values in p1310 ... p1312
can cause the motor to overheat and switch off (trip) the inverter due to overcurrent.
If the message A07409 appears, you must not increase any of the parameters.
Procedure
Proceed as follows to set the voltage boost:
1. Switch off the motor with a setpoint of just a few revolutions per minute.
2. Check whether the motor rotates smoothly.
3. If the motor rotates eccentrically or even stops, increase the voltage boost p1310 until the
motor rotates smoothly.
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Converter with the CU240B-2 and CU240E-2 Control Units
Operating Instructions, 01/2016, FW V4.7 SP6, A5E34259001B AC