Bypass With Synchronization Without Overlap - Siemens SINAMICS S120 Function Manual
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5.22 Bypass
5.22.3
Bypass with synchronization without overlap
Description
When "bypass with synchronization without overlap (p1260 = 2)" is activated, contactor K2 to
be closed is only closed when contactor K1 has opened (anticipatory type synchronization).
During this time, the motor is not connected to the line supply so that its speed is determined
by the load and the friction. This type of bypass is therefore suitable for drives with high
inertia (see the note below).
Synchronization setpoint p3809 is used to correct a phase rotation in the signal sensing of
the voltage actual values (p3809 = -180°...179,90°). Further, using this parameter, the
setpoint angle of the motor voltage can be advanced in a range up to a maximum of 20°el (=
maximum value, p3813), in order to compensate for a friction/load-dependent speed
decrease during the bypass switchover.
The phase position of the motor voltage before synchronization can be set using p3809 to
enable an "advance start" before the line supply to which synchronization should be carried
out. As a result of the motor braking in the short time in which both contactors are open,
when closing contactor K2, now a phase and frequency difference of approximately zero
must be obtained. If, when switching over, the angular difference would be > 20°el, then
current surges be expected that cannot be neglected. This is the reason that synchronism is
only reached if the angular difference is ≤ p3813 (maximum of 20°el).
Compensating a speed decrease using p3809 only makes sense if the motor is evenly
loaded during the switchover period. For instance, for conveyor belts, depending on the
process environment, the load can change during the bypass sequence.
If, during the switchover process, the angular difference is more than 20°el - or if the load for
each bypass operation differs, then the "Bypass with synchronization with overlap
(Page 284)" mode must be used.
A voltage sensing module VSM10 is required for this type of bypass which measures the line
supply voltage required for the drive to be synchronized.
For the function to run correctly, the moment of inertia of the drive and the load must be
sufficient.
Note
A sufficiently high moment of inertia is characterized by a change in the motor speed during
opening of the contactors K1 and K2 that is approximately equal to the rated slip.
Further, it must be ensured that at the switchover instant, the motor is not significantly
braked as a result of external effects (e.g. friction).
288
Function Manual, 11/2017, 6SL3097-4AB00-0BP5
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