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Advantages and disadvantages of soft starter, online and bypass

After the soft starter with bypass is completed (measured Ia, Ib, Ic<110%In), it will give a bypass switching signal to the bypass contactor KM3 by R2A/R2C, and switch to the power frequency. At this time, the internal circuit of the soft starter will still provide various detection and protection functions, which is not what the title means (it is inferred that the bypass type does not have loop detection capability after switching to the bypass), so the bypass contactor is not A thermal relay is required to achieve overload, short circuit, phase loss, etc. protection. The soft starter with bypass will no longer have a large current of the main circuit to pass through after the start is completed (the current and voltage are read through the internal transformer). Therefore, only electronic components are self-heating, the heat dissipation pressure is reduced, and the lifespan is significantly increased. Therefore, if there is no special requirement for space, the connection method with bypass is basically adopted in various fields.


To sum up, the advantages of the online type (without bypass type) have two points: 1. Save the external contactor and reduce the economic cost of the entire cabinet. 2. No additional contactor is required, which greatly reduces the space requirement, which is very suitable for occasions with large space requirements. Of course, the shortcomings are also obvious. The entire operation process is completed within the soft start, the heat generation is significant, and the product life is affected. Bypass type (with bypass contactor) also has 2 advantages: 1. Switch to bypass after startup, only the detection circuit is inside the soft start, heat dissipation is easy, and the service life is significantly increased. I have seen ATS48 that has been used for 12 years. Soft starter, the external bypass used is still running normally. 2. After the startup is completed, it still has various protections to prevent failures caused by various problems after switching to the bypass, which can not be detected and damage the components, and the external bypass will be more convenient for inspection and maintenance. The disadvantage is that contactors, especially high-current contactors, are often large in size, resulting in an increase in the volume of the entire power distribution cabinet. The added cost of the contactor is often not a small sum, and there is no economic advantage.