ABB 软起动器系列；PST
3.软启动器工作原理
Working principle of 3. soft starter
软启动器采用三相反并联晶闸管作为调压器，将其接入电源和电动机定子之间。这种电路如三相全控桥式整流电路。
The soft starter uses a three phase anti parallel thyristor as a voltage regulator to connect it to the power of the motor and the stator of the motor. This kind of circuit is a three-phase fully controlled bridge rectifier circuit.
当使用软启动器启动电动机时，晶闸管的输出电压逐渐增加，电动机逐渐加速，直到晶闸管全导通，电动机工作在额定电压的机械特性上，实现平滑启动，降低启动电流，避免启动过流跳闸。
When the motor is started using the soft starter, the thyristor output voltage increases, the motor accelerates gradually until the thyristor wholeconduction motor working in the mechanical properties of rated voltage, to achieve a smooth start, reduce the starting current, avoid starting over-current trip.
待电机达到额定转数时，启动过程结束，软启动器自动用旁路接触器取代已完成任务的晶闸管，为电动机正常运转提供额定电压，以降低晶闸管的热损耗，延长软启动器的使用寿命，提高其工作效率，又使电网避免了谐波污染。软启动器同时还提供软停车功能，软停车与软启动过程相反，电压逐渐降低，转数逐渐下降到零，避免自由停车引起的转矩冲击。
When the motor reaches the rated speed, the startup process end, soft starter thyristor automatic bypass contactor with substituted completion pipe, provide the rated voltage of the normal operation of the motor, to reduce the heat loss of the thyristor soft starter, prolong the service life, improve the work efficiency, but also to avoid network harmonic pollution. The soft starter also provides soft parking function. The soft parking process is opposite to the soft start process. The voltage gradually decreases, and the revolution gradually decreases to zero, avoiding the torque impact caused by free parking.
