Siemens Sinamics S120 Function Manual page 212

Vector control
4.25 Bypass
When the motor is switched on in a non-synchronized manner, an equalizing current flows
that must be taken into account when the protective equipment is designed.
When the converter retrieves the motor from the line supply, initially contactor K2 is opened,
and after the excitation time has expired, contactor K1 is closed. The drive converter then
connects to the rotating motor and the motor is fed from the drive converter.
In this case, contactor K2 must be designed/selected to be able to switch inductive loads.
Contactors K1 and K2 must be interlocked so that they cannot simultaneously close.
The "flying restart" function must be activated (p1200).
Figure 4-33
Activation
The bypass without synchronization (p1260 = 3) can be triggered by the following signals
(p1267):
● Bypass by means of control signal (p1267.0 = 1):
● Bypass at speed threshold (p1267.1 = 1):
comparison value condition prevents the bypass from being reactivated straight away if
the actual speed is still above the bypass speed threshold (p1265) after switching back to
The bypass time, debypass time, bypass speed variables and the command source for
changing over are set using parameters.
210
Circuit example, bypass without synchronization
The bypass can be activated by means of a digital signal (p1266) (e.g. from a higher-level
control system). If the digital signal is withdrawn, a changeover to converter operation is
initiated once the bypass delay time (p1263) has expired.
Once a certain speed is reached, the system switches to bypass (i.e. the converter is
used as a start-up converter). The bypass cannot be connected until the speed setpoint is
greater than the bypass speed threshold (p1265).
The system reverts to converter mode when the setpoint (on the input of the ramp-
function generator, r1119) falls below the bypass speed threshold (p1265). The setpoint >
converter operations.
Function Manual, (FH1), 01/2012, 6SL3097-4AB00-0BP2
Drive functions