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Soft Start Method Classification

Sep 10, 2020

Soft start method classification


Soft start is a new technology that has emerged in recent years with the development of electronic technology. When starting, the air circuit breaker uses a soft starter (a thyristor voltage regulator) to gradually increase the voltage from a lower value to the rated position. Then use the bypass contactor KM (a kind of electromagnetic switch).


The main composition of the soft start is the three-phase reverse parallel thyristor and its electronic control circuit connected between the electric pump and the controlled motor. Use different methods to control the conduction angle of the three-phase parallel thyristor so that the input voltage of the controlled motor changes according to different requirements, and different functions can be realized. Soft starters and inverters are two completely different products. The frequency converter is used where speed regulation is required. Its output not only changes the voltage but also changes the frequency at the same time; the soft starter is actually a voltage regulator. Used when the motor is started. The output only changes the voltage without changing the frequency. The frequency converter has all the soft starter functions, but its price is much more expensive than the soft starter, and the structure is much more complicated.

Soft start mode

    (1) Slope boost soft start. This kind of starting method is the simplest. It does not have a current closed-loop control, and only adjusts the conduction angle of the thyristor to increase it in a certain A relationship with time. The disadvantage is that due to the unlimited current, in the motor starting process, sometimes a large inrush current is generated to damage the thyristor, which has a greater impact on the power grid. It is rarely used in practice.

    (2) The ramp value flow soft start. This kind of starting method is that the starting current gradually increases in the initial stage of the motor starting, and when the current reaches the preset value, it remains constant (stage 11 to a). Until the start is completed. During the starting process, the rate of current rise and change can be adjusted and set according to the motor load. If the current rise rate is large, the starting torque is large and the starting time is short. This startup method is the most widely used startup method, especially suitable for the startup of fans and pumps.

    (3) Step start. Startup means that the starting current quickly reaches the set value in the shortest time, which is a step start. By adjusting the starting current setting value, a quick start effect can be achieved.

    (4) Pulse impact start. At the beginning of the start-up phase, let the QT in a short period of time. With a relatively large current for a period of time, then fall back, and then increase linearly according to the original set value. Start with constant current. This starting method is rarely used in general loads, and is suitable for starting occasions with heavy loads and large static friction that needs to be overcome.