Zhejiang Shuyi Electric Co. Ltd

The so-called soft start is that the voltage gradually increases from zero to the rated voltage, and the current also changes from small to large. During the whole process of starting the motor, there will be no shock torque, but a smooth start-up operation. There are generally the following startup methods:Ramp boost soft start, ramp constant current soft start, step start, pulse impact start, voltage double ramp start, current limit start, etc.

1. Ramp boost soft start

This kind of starting method is the simplest, it does not have current closed-loop control, and only adjusts the conduction angle of the thyristor to increase it as a function of time. The disadvantage is that, due to no current limit, in the process of starting the motor, a large inrush current is sometimes generated to damage the thyristor, which has a great impact on the power grid, and is rarely used in practice.

2. Ramp constant current soft start

This kind of starting method is that the starting current gradually increases in the initial stage of motor starting, and when the current reaches the preset value, it remains constant until the start is completed. This starting method is the most widely used starting method, especially suitable for the starting of fans and pumps.

3. Step start

Start the machine, that is, make the starting current reach the set value quickly in the shortest time, which is the step start. By adjusting the setting value of starting current, the effect of fast starting can be achieved.

4. Pulse impact start

At the beginning of the start, let the thyristor conduct a large current for a period of time in a very short time, then fall back, and then rise linearly according to the original set value, and connect it to a constant current start. This starting method is rarely used in general loads, and is suitable for starting occasions with heavy loads and large static friction needs to be overcome.

5, voltage double ramp starting

In the process of starting, the output torque of the motor increases with the voltage, and an initial starting voltage Us is provided when starting. Us is adjustable according to the load, and the Us is adjusted to be greater than the load static friction torque. When the output voltage reaches the speed voltage Ur, the motor also basically reaches the rated speed. The soft starter automatically detects the speed voltage during the starting process, and when the motor reaches the rated speed, the output voltage reaches the rated voltage.

6. Current limiting starting

Current limiting starting is the soft starting mode that limits the starting current of the motor to a certain set value. The output voltage increases rapidly from zero until the output current reaches the pre-set current limit Im, and then keeps the output current. The advantage of this starting mode is that the starting current is small and can be adjusted as required.

1. Current limiting start

Current-limiting startup is to limit the startup current of the motor. It is mainly used in light-load startup equipment. It can visually see the startup current. At the same time, it is difficult to obtain the startup voltage drop during startup. The lowering space loses the starting torque, which is not good for the motor.

2. Ramp voltage start

Ramp voltage start means that the voltage rises linearly from small to large. It is mainly used in heavy-duty starting equipment. It realizes the transformation of the traditional step-down starting from step-less to stepless, and the parabolic rise of starting torque characteristics is opposite to dragging. The system is advantageous, the startup is smooth, and the flexibility is good to make it an advantage. It has better protection for the drag system and prolongs the service life of the drag system. But the larger starting current is its disadvantage.

3. Torque plus sudden jump control start

Torque plus kick control startup is to add a voltage kick on the basis of voltage ramp control startup. It is mainly used in equipment with large static inertia, such as fan load and other equipment that is difficult to start with voltage ramp. It uses the kick torque to overcome the static resistance torque of the motor at the moment of starting, and then increases the torque parabolically to shorten the starting time. However, its disadvantage is that a sudden power outage will send a surge current of 100 milliseconds to the grid and then bring a large current shock to the grid.


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