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As we all know, the main function of soft starter is to reduce the starting voltage and current. The three-phase reverse parallel thyristor is used as voltage regulator, which has the advantages of small starting current, stable and reliable starting speed and small impact on the power grid. The starting curve can be adjusted according to the actual working conditions on site, so as to reduce the impact force on the equipment during starting, reduce the damage to the equipment and prolong the service life.

So, is the soft starter still energy-saving?

To answer this question, let's review the working principle of soft starter: when the soft starter starts the motor, the output voltage of the thyristor increases gradually, and the motor starts under pressure gradually until the thyristor is fully connected to realize the smooth start of the motor full voltage.

At the same time, soft starter also provides soft stop function, which is opposite to the soft start process. The voltage gradually decreases and the number of turns decreases to zero gradually, avoiding torque impact caused by free stop and reducing equipment loss.

Through the analysis of the working principle, it is found that the main function of soft starter is the start and stop of motor, and the start and stop of motor is no more than 60 seconds. From this point of view, the energy saving effect of soft starter is very small.

However, when reading other documents, the author found that the UK had made comparative tests on soft start products with different control principles, and the results were as follows:

1. The energy saving effect is obvious when the load rate is less than 30%, and the low power factor is less than 0.4;

2. When the medium load (40% - 50%) is medium power factor (0.5-0.6), the loss absorbed by soft starter is equivalent to the energy saving power, mainly because the iron loss saved is offset by the increase of copper loss, which makes it difficult to save energy;

3. When the load is higher than 70%, the energy saving effect is almost no when the high power factor is more than 80%;

4. Under the rated load, the power consumption is actually increased, mainly the voltage drop loss of the thyristor series into the main circuit.