Bypass; Overview - Siemens SINAMICS S120 Function Manual

5.22

Bypass

5.22.1

Overview

The bypass function controls two contactors via digital outputs of the drive converter and
evaluates the feedback signals of the contactors via digital inputs (e.g. via TM31). This circuit
allows the motor to be operated using the converter or directly on the supply line. The
contactors are activated by the converter. The feedback signals for the contactor positions
have to be returned to the converter.
The bypass circuit can be implemented in two ways:
● Without synchronizing the motor to the line supply and
● Synchronizing the motor to the line supply.
The following applies to all bypass versions:
● The bypass switch is also shut down (the motor coasts down) when one of the "OFF2" or
"OFF3" control word signals is canceled. When "OFF1" is withdrawn, the motor remains
connected to the line supply.
● Exception:
When required, the bypass switch can be interlocked by a higher-level controller so that
the drive converter can be completely powered-down (i.e. including the control
electronics) while the motor is operated from the line supply. The contactor interlocking
should be implemented on the plant/system side.
● When the drive is started up again after POWER ON, the status of the bypass contactors
is evaluated. After powering up, the converter can thereby change straight into "Ready to
start and bypass" status. This is only possible if the bypass is activated via a control
signal, the control signal (p1266) is still present once the system has been ramped up,
and the automatic restart function (p1210 = 4) is active.
The bypass is automatically started again when restarting. To accelerate the motor to the
setpoint speed and/or to synchronize to the line supply, the pulses are enabled, possibly
with the motor already rotating. In this case, we recommend that the "Flying restart"
function (p1200 = 1) is activated in order to avoid high current peaks.
● Changing the converter into "Ready to start and bypass" status after powering up, is of a
higher priority than switching back on automatically.
● Monitoring of the motor temperatures using temperature sensors is active while the
converter is in one of two states "Ready to start and bypass" or "Ready for operation and
bypass".
● The two motor contactors must be designed for switching under load.
Note
The examples contained in the following descriptions are only basic circuits designed to
explain the basic function. The dimensions of specific circuit configurations (contactors,
protective equipment) must be calculated for specific systems.
Drive functions
Function Manual, 11/2017, 6SL3097-4AB00-0BP5
Vector control
5.22 Bypass
283