For factory motors, what power level requires the use of a soft starter, and for motors below what power level can they be started directly?

There is no mandatory requirement for this; the 1600KW unit I’ve used can start directly

It depends on the capacity of the transformer you have; if the transformer capacity is sufficient, it’s possible to start it directly with 160kW

Dear sea friend, Alai will give a brief explanation for your reference! Generally speaking, **the standards stipulate that when the motor starts frequently, the voltage drop on the busbar should not be lower than 10%** ； When starting infrequently, the bus voltage drop should not be less than 20% ； When the motor is not started frequently and shares a transformer with lighting or other loads sensitive to voltage fluctuations, the voltage drop during motor startup must not exceed 15%. Based on this principle, you can conduct a voltage drop calculation (taking into account the transformer’s capacity, the incoming circuit breaker, and the busbar dimensions); if the requirements are met, then it may not be necessary to use a soft starter ； However, due to various factors such as a large motor capacity or the critical nature of the driving equipment, soft starters can also be used. This not only helps to reduce the impact of high starting currents on the power distribution system and lowers the incidence of electrical failures, but it also reduces the stress on the equipment through soft starting. If the requirements are not met, it is necessary to use a soft starter ； Otherwise, it is necessary to increase the capacity of the distribution transformer, the size of the copper busbars, and the rated capacity of the incoming circuit breakers.

We stipulate that motors with 22 KW or less with two poles, those with 30 KW or less with four poles, and those with 55 KW or less with six poles can start directly, without the need for soft-start or autotransformer-based starting devices

Full-voltage starting of electric motors: not more than 30% of the transformer’s capacity. According to page 661, section middle of the third edition of the \"Manual for Industrial and Civil Power Distribution Design\", the condition for full-voltage starting of cage-type motors in low-voltage power distribution design can be simplified as follows: the voltage on the power distribution busbar at the time of motor startup must be no less than 85% of the system’s nominal voltage. Generally, as long as the rated power of the motor does not exceed 30% of the rated capacity of the power supply transformer, it can be started at full voltage. Detailed calculations are only required when the estimation results are in borderline cases. Requirement 5.7.6 of the DGJ08-100-2003 Regulations on Electrical Installations for Low-Voltage Users in Shanghai states: \"The capacity of motors that may be started directly shall be less than 8% of the capacity of the supply transformer, while the capacity of fire-fighting equipment that may be started directly shall be less than 15% of the capacity of the supply transformer.\"”

http://bbs.hcbbs.com/forum.php?mod=viewthread&tid=1593095&page=1#pid16722340 A Brief Discussion on the Selection of Motor Starting Methods, journal article