We know that the synchronous speed is the number of magnetic polesPThe principle of motor speed selection is to make it as close as possible to the speed of the production machinery to simplify the transmission. Three-phase asynchronous motor speed is close to synchronous speed, if you want to adjust its speed, you can use to change the power frequencyf, change slip rateSAnd change the number of magnetic polesPAnd so on three methods.

       Change the power frequency: The premise of this method is to use AC power. Generally, the thyristor frequency conversion speed regulation system is used, and the alternating current is first converted to the direct current with adjustable voltage, and then converted to the alternating current with adjustable frequency. The reason why this method is not widely used is that the equipment is too complex and the price is very expensive.

        Change slip rate: This method can only be applied to wound rotor asynchronous motors. Because the resistance is usually in series in the rotor loop, the slip rate is changed by changing the resistance of the rotor loop to speed regulation. Generally, only winding rotors can connect the speed control resistance outside the machine through the slip ring and brush. This method is rarely used to adjust the speed of the machine tool motor, because its power consumption is relatively large, but the efficiency is not high.

        Change the number of magnetic poles: Because the number of magnetic poles can only be changed in pairs, it can only be adjusted in stages, and generally can be adjusted in two, three or four speeds. It is commonly used on the machine tool to change the triangle connection to the double star connectionThree-phase asynchronous motorTwo-speed speed from four to two.

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