1. Direct start with full pressure
When both the grid capacity and the load allow full-voltage direct start, full-voltage direct start can be considered. The advantages are easy operation and control, simple maintenance, and relatively economical. It is mainly used for starting small power motors. From the perspective of saving electric energy, this method is not suitable for motors larger than 11kW.
2. Auto-decompression start
The multi-tap voltage reduction of the autotransformer can not only adapt to the starting needs of different loads, but also obtain greater starting torque. It is a pressure reduction starting method that is often used to start larger capacity motors. Its biggest advantage is its large starting torque. When its winding tap is at 80%, the starting torque can reach 64% of that at direct start. And the starting torque can be adjusted by tapping. It is still widely used today.
3.Y-Δ start
For a squirrel-cage asynchronous motor whose stator winding is connected in delta during normal operation, if the stator winding is connected in star shape when starting and then connected in delta after starting, the starting current can be reduced and the impact on the power grid can be reduced. impact. This starting method is called star-delta decompression start, or simply star-delta start (Y-Δ start). When using star-delta starting, the starting current is only 1/3 of the original direct starting based on delta connection. If the starting current during direct start is calculated as 6~7Ie, then the starting current during star-delta start is only 2~2.3 times. This means that when star-delta starting is used, the starting torque is also reduced to 1/3 of the original direct starting using delta connection. Suitable for no-load or light-load starting situations. Compared with any other pressure reducing starter, it has the simplest structure and the cheapest price. In addition, the star-delta starting method has another advantage, that is, when the load is light, the motor can be run in star connection. At this time, the rated torque can match 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 the thyristor to realize the voltage-regulated starting of the motor. It is mainly used for the starting control of the motor. The starting effect is good but the cost is high. Due to the use of thyristor components, harmonic interference is greater when the thyristor is working, which has a certain impact on the power grid.
In addition, fluctuations in the power grid will also affect the conduction of thyristor components, especially when there are multiple thyristor devices in the same power grid. Therefore, the failure rate of thyristor components is high, and because it involves power electronics technology, the requirements for maintenance technicians are also high.
5. Frequency converter
Frequency converter is a motor control device with the highest technical content, the most complete control functions 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 electronics technology and microcomputer technology, the cost is high and the requirements for maintenance technicians are also high. Therefore, it is mainly used in fields that require speed regulation and have high speed control requirements.
