Five starting modes of motor
1. Full pressure direct start
Under the condition that full voltage direct start is allowed in both grid capacity and load, full voltage direct start can be considered. The advantages are convenient 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 should not be used for motors larger than 11kw.
2. Self coupling decompression start
Using the multi tap decompression of autotransformer can not only meet the needs of different load starting, but also get a larger starting torque. It is a decompression starting method often used to start large capacity motors. Its biggest advantage is that the starting torque is large. When the winding tap is at 80%, the starting torque can reach 64% of the direct starting torque. And the starting torque can be adjusted by tapping. It is still widely used.
3、Y- Δ start-up
For squirrel cage asynchronous motors with delta stator winding in normal operation, if the stator winding is connected into a star at start-up and then into a triangle after start-up, the starting current can be reduced and its impact on the power grid can be reduced. Such starting mode is called star delta decompression starting, or star delta starting (Y- Δ Start). When star delta starting is adopted, the starting current is only 1/3 of the original direct starting according to the triangle connection method. If the starting current during direct starting is calculated as 6 ~ 7ie, the starting current is only 2 ~ 2.3 times during star delta starting. 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 triangle connection method. It is suitable for no-load or light load starting. And compared with any other pressure reducing starter, its structure is the simplest and the price is the cheapest. In addition, the star delta starting method has another advantage, that is, when the load is light, the motor can run under the star connection method. At this time, the rated torque and load can be matched, which can improve the efficiency of the motor and save power consumption.
4. Soft starter
This is to use the phase-shifting voltage regulation principle of thyristor to realize the voltage regulation start of motor, which is mainly used for the start control of motor. The starting effect is good, but the cost is high. Due to the use of thyristor components, the harmonic interference of thyristor during operation 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 components, 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.