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What are The Methods to Reduce The Starting Current of The Motor?

What are The Methods to Reduce The Starting Current of The Motor?插图

1. Direct boot

Direct starting is to connect the stator winding of the motor directly to the power supply and start it under the rated voltage. It has the characteristics of large starting torque and short starting time, and it is also the simplest, most economical and most reliable starting method. The current is large during full-voltage starting, but the starting torque is not large, the operation is convenient, and the starting is fast. However, this starting method requires relatively large grid capacity and load, and is mainly suitable for starting motors below 1W.

2. Series resistance start

Motor series resistance start, which is a method of step-down start. During the starting process, a resistor is connected in series in the stator winding circuit. When the starting current passes, a voltage drop is generated on the resistance, which reduces the voltage applied to the stator winding, so that the purpose of reducing the starting current can be achieved.

3. Self-coupling transformer start

The use of multi-tap decompression of autotransformer can not only meet the needs of starting with different loads, but also obtain greater starting torque. It is a decompression starting method often used to start large-capacity motors. Its biggest advantage is that the starting torque is relatively large. When its winding tap is at 80%, the starting torque can reach 64% of that of direct starting, and the starting torque can be adjusted through the tap.

4. Star delta decompression start

For a squirrel-cage asynchronous motor with a delta-connected stator winding in normal operation, if the stator winding is connected into a star shape at start-up and then connected into a delta shape after starting, the starting current can be reduced and its impact on the power grid can be reduced. shock. Such a starting method is called a star-delta decompression start, or simply a star-delta start (y-& start). When using star-delta starting, the starting current is only 1/3 of the original direct starting according to the delta connection. When starting in star delta, the starting current is only 2-2.3 times. That is to say, when the star-delta connection is used, the starting torque is also reduced to 1/3 of the original direct start according to the delta connection. Suitable for no-load or light-load starting occasions. And compared with any other decompression 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 be operated in star connection. At this time, the rated torque can be matched with the load, which can improve the efficiency of the motor and thus save power consumption.

5. Inverter start (soft start)

Inverter 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 electronic technology and microcomputer technology, the cost is high and the requirements for maintenance technicians are also high, so it is mainly used in fields that require speed regulation and have high requirements for speed control.

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