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What should I do if the external soft starter cannot switch the bypass?

Jan 04, 2021

What should I do if the external soft starter cannot switch the bypass?

Some of our customers have encountered the situation that the external soft starter cannot switch the bypass when purchasing other soft starters. Why did you encounter this situation? How to solve it after encountering it?



When we solve the problem, we should first understand how the soft starter and bypass control are switched.


After the soft starter is started, it will trigger the bypass contactor to close by an internal signal, allowing the main circuit current to be bypassed from the thyristor to the bypass contactor circuit, and the bypass contact will change from normally open to normally closed. At this time, the bypass contactor will be closed, and the main circuit will switch to power frequency.



If the external soft starter does not switch the bypass, the reason may be: there is a voltage drop when the motor starts, causing the voltage to be too low, and the bypass contactor is not voltage enough when switching, causing poor contact and affecting normal startup.


Solution:


1. Extend the starting time, such as changing 16 seconds to 30 seconds.


2. Change the starting mode. Use current limiting starting to limit the current within 300% or 400% of the rated current. At this time, the start process of the soft starter is: after pressing the start button, the current slowly rises from 0 and stops when it reaches the limit. As the motor speed gets faster and faster, after reaching the rated speed, the current drops below the rated current. At this time, the bypass contactor is switched on and switched to complete the start.