u small slurry pump manual

how to choose the motor for centrifugal pump

How to choose the motor for centrifugal pump

When both the power grid and the load are allowed, the pump motor should be started directly because it is easy to control and economical.

Auto-decompression start is often used to start larger-capacity squirrel-cage asynchronous motors. Although auto-decompression start is an old-fashioned starting device, the multi-tap decompression using autotransformer can adapt to a variety of loads. It is required to start, and it can get a larger starting torque. In addition, it is widely used because it is equipped with a thermal relay and a low voltage release and has a perfect overload and voltage loss protection.

The star-delta starting method has good current characteristics, but poor torque characteristics, so it is only suitable for no-load or light-load starting occasions, but this method has the simplest structure and the cheapest price, which can save power consumption during light-load operation.

All of the above start methods are step-by-step decompression start, and have obvious disadvantages, that is, a secondary impulse current occurs during the start.

Comparison of advantages and disadvantages of decompression start, soft start, and frequency conversion start

The decompression start, the star-delta start is common, the disadvantage is that the start torque is small, and it is only suitable for no-load or light-load start. The advantage is that it is cheap.

Soft start, you can set the start time and start initial torque to achieve soft start and soft stop of the pump, and can limit the start current, and the price is moderate.

Frequency conversion start, can start smoothly according to the set time, and let the equipment run at the set frequency, the price is higher.

The difference between soft start and traditional decompression start is:

①No 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.

②It has a soft stop function, that is, it decelerates smoothly and stops gradually. 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.

③Starting parameters are adjustable, and can be selected according to load conditions and power grid protection characteristics, and can be adjusted to the best starting current freely and steplessly.

Note that soft starters and inverters 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.