Siemens SINAMICS G120 Operating Instructions Manual page 292

Advanced commissioning
6.7 Application-specific functions
Changeover operation between line and inverter operation
When switching over to direct online operation, contactor K1 is opened after the inverter
pulses have been inhibited. The system then waits for the de-energization time of the motor
and then contactor K2 is closed so that the motor is connected directly to the line.
When the motor is switched to the line supply, an equalizing current flows that must be taken
into account when the protective equipment is selected and dimensioned.
When changing over to inverter operation, initially contactor K2 must be opened and after
the de-excitation time, contactor K1 is closed. The inverter then captures the rotating motor
and the motor is operated on the inverter.
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Converter with CU230P-2 Control Units
Operating Instructions, 04/2015, FW V4.7 SP3, A5E34257946B AB