Bypass With Synchronization Without Overlap - Siemens SINAMICS S120 Function Manual

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Bypass with synchronization without overlap

Function description

If the function "Bypass with synchronization without overlap (p1260 = 2)" is activated, contactor

K2 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. For the function to run correctly, the moment of inertia of the drive and the

load must be sufficiently high.

A sufficiently high moment of inertia is characterized by a change in the motor speed when

contactors K1 and K2 are opened, which 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).

Synchronization setpoint p3809 is used to correct a phase rotation in the signal sensing of the

voltage actual values (p3809 = -180° to 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

Drive functions

Function Manual, 06/2019, 6SL3097-5AB00-0BP2

Circuit example: Bypass with synchronization without overlap

Vector control