The most familiar electric equipment for electrical operators should be the motor. There are many ways to start the motor, including direct start, self coupling decompression start and y- Δ Step down start, soft starter start, frequency converter start, etc. So what's the difference between them?

1. Full pressure direct start

Under the condition that full voltage direct start is allowed in both power grid capacity and load, full voltage direct start can be considered.

The utility model has the advantages of convenient operation and control, simple maintenance and economy. It is mainly used for starting small power motors. From the perspective of saving electric energy, this method should not be used for motors greater than 11kw.

2. Self coupling decompression start

Using multi tap decompression of autotransformer can not only meet the needs of different load starting, but also obtain greater starting torque. It is a decompression starting mode often used to start large capacity motors.

Its biggest advantage is that the starting torque is large. When the winding tap is 80%, the starting torque can reach 64% of that of direct starting. And the starting torque can be adjusted through tap. It is still widely used.

3、Y- Δ start-up

For the squirrel cage asynchronous motor with triangular stator winding in normal operation, if the stator winding is connected into a star at start-up and then connected into a triangle after start-up, the starting current can be reduced and its impact on the power grid can be reduced. This startup mode is called star delta decompression startup, or star delta startup (y)- Δ Start).

When star delta starting is adopted, the starting current is only 1 / 3 of that when it is started directly according to the triangular connection method. If the starting current during direct start is calculated as 6 ~ 7ie, the starting current is only 2 ~ 2.3 times during star delta start. That is to say, when star delta starting is adopted, the starting torque is also reduced to 1 / 3 of the original direct starting according to the triangular connection method.

It is suitable for no-load or light load start-up. And compared with any other decompression starter, its structure is the simplest and the price is the cheapest. In addition, star delta starting mode has another advantage, that is, when the load is light, the motor can run under star connection. At this time, the rated torque can be matched with the load, which can improve the efficiency of the motor and save power consumption.

4. Soft starter

This uses the phase-shifting voltage regulation principle of thyristor to realize the voltage regulation start of motor. It is mainly used for the start control of motor. The start effect is good, but the cost is high. Due to the use of thyristor, the harmonic interference of thyristor is large, which has a certain impact on the power grid.

In addition, the fluctuation of power grid will also affect the conduction of thyristor elements, especially when there are multiple thyristor devices in the same power grid. Therefore, the failure rate of thyristor components is high, because it involves power electronics technology, so the requirements for maintenance technicians are also high.

5. Frequency converter

Frequency converter is the motor control device with the highest technical content, the most complete control function and the best control effect in the field of modern motor control. It adjusts the speed and torque of the motor by changing the frequency of the power grid. Because it involves power electronic technology and microcomputer technology, the cost is high and the requirements for maintenance technicians are high. Therefore, it is mainly used in the fields requiring speed regulation and high requirements for speed control.

Comparison of advantages and disadvantages of reduced pressure start, soft start and variable frequency start

Decompression start, the common star delta start, has the disadvantage of small starting torque and is only suitable for no-load or light load start. The advantage is that the price is cheap.

Soft start: the starting time and initial starting torque can be set to realize soft start and soft stop of the equipment, limit the starting current, and the price is moderate.

Variable frequency startup can start smoothly according to the set time, and make the equipment run at the set frequency, with high price.