How is the soft starter and bypass control switched? -Solutions - Huaqiang Electronic Network

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After the soft starter is activated, it first cuts its own power and then engages the bypass. Or does the soft start operate by turning on the bypass, then shutting off the soft starter? Let me clarify: once the soft start process is complete, the internal signal triggers the bypass contactor to switch the main circuit current from the thyristor to the bypass contactor. This ensures a smooth transition to full voltage operation.

Bypass contactors can be either built-in or external, and their activation methods vary. Older models typically used external bypass contactors, such as the 3RW34 or 3RW22 series. These required an external signal to activate the contactor coil. Once the soft start was completed, the contactor would close, redirecting the current to the power frequency supply. However, modern soft starters like the 3RW30, 3RW40, or 3RW44 often come with built-in bypass contactors. In these cases, the soft starter itself sends the signal to close the contactor, eliminating the need for external control. For more complex setups, such as one-to-many configurations, external signals may still be necessary to trigger the bypass contactor.

The schematic of a soft starter usually consists of three main components, and understanding its working principle can help resolve many issues. Here's a brief overview of how it works:

Taking the first motor as an example, the soft start process works like this: when the start button S11 is pressed, and no alarm is triggered, the soft starter K8 gets energized. This closes the normally open contact of K8, allowing the starting contactor K10 (a delayed disconnecting contactor) to energize. Once K10 is active, its normally open contacts close, which in turn energizes the main contactor K1. As the soft starter begins to start the motor, the contactor K9 closes, and K12 becomes self-latched. After a set delay, K10 opens, followed by the disconnection of K1, which turns off the soft starter. At this point, the motor is powered directly through K12. This system allows each motor to be started one at a time without affecting the others. After starting, the bypass contactor closes, and the soft starter delays power delivery for a short period. If only one motor is being driven, as long as the soft starter has sufficient power capacity, there should be no issue with the bypass contactor.