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Talking about the use of soft starter

Sep 07, 2020

Talking about the use of soft starter

 1. What is a soft starter?

      The soft starter is a new device used to control the squirrel cage asynchronous motor. It is a novel motor control device integrating motor soft start, soft stop, light load energy saving and multiple protection functions. It is called Soft Starter abroad. Its main composition is a three-phase parallel thyristor and its electronic control circuit connected in series between the power supply 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.

      2. What is the application range of the soft starter?

      In principle, squirrel-cage asynchronous motors can be applied to various applications that do not require speed regulation. The current application range is AC 380V (or 660V), and the motor power ranges from several kilowatts to 800kW. The soft starter is especially suitable for various pump loads or fan loads, where soft start and soft stop are required.

      3. What is the difference between soft start and traditional decompression start?

      The traditional decompression starting methods of squirrel cage motors include Y-△ starting, auto-coupling decompression starting, reactor starting and so on. These starting methods are all step-decompression starting, with obvious shortcomings, that is, a secondary surge current occurs during the starting process. Due to the backward technology of the traditional decompression starting method, the country has clearly ordered it to be eliminated.

The difference between soft start and traditional decompression start is:

(1) No inrush current. When the soft starter starts the motor, by gradually increasing the conduction angle of the thyristor, the motor starting current linearly rises from zero to the set value. There is no impact on the motor, which improves the reliability of power supply, starts smoothly, reduces the impact torque on the load machinery, and prolongs the service life of the machine.

    (2) There is a soft stop function, that is, smooth deceleration and gradual shutdown. It can overcome the shortcomings of instantaneous power failure, reduce the impact on heavy-duty machinery, avoid the water hammer effect of the elevation water supply system, and reduce equipment damage.

    (3) The starting parameters are adjustable, which can be selected according to the load conditions and the characteristics of the grid relay protection, and can be freely steplessly adjusted to the best starting current.

      4. What is the difference between it and the inverter?

      Soft starters and frequency converters are two completely different products. The frequency converter is used where speed regulation is required, and its output not only changes the voltage but also changes the frequency at the same time; the soft starter is actually a voltage regulator, when used for motor starting, 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.

      Most soft starters have bypass contactor contacts on both sides of the thyristor. The advantages are:

(1) The harmonics generated by the soft starter can be avoided when the motor is running

(2) The soft-start thyristor only works when starting and stopping, which can prevent the thyristor from heating during long-term operation and prolong its service life.

(3) Once the soft starter fails, the bypass contactor can be used as an emergency backup.