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Motor series resistor speed control principle Motor series resistor speed regulation principle

The rated torque Tn is the torque generated by the motor under the conditions of rated voltage and rated current. The speed at this moment is called the rated speed Nn. Start torque Tst, is the torque when the motor starts, then n = 0, s = 1, for the winding induction motor, the motor circuit in series resistance can improve the motor starting torque curve 1 For the natural characteristics, string into the resistor R1 = 0, the curve characteristics of 2,3,4 for the man-made characteristics, the series resistance value R2, R3, R4. When the load torque is constant, the speed of the motor is related to the resistance of the circuit in the rotor circuit. As can be seen from the figure, after the resistor is connected in series, the maximum torque Tm and the synchronous speed N0 of the motor are the same, but the critical slip The rate of increase Sm increases with the increase of the rotor resistance R. The larger the resistance, the softer the mechanical properties and the lower the motor speed. String into the resistance is too small, the starting torque is not enough. Therefore, changing the size of the external resistor can speed within a certain range.

Motor speed

KM1 is closed, the rotor loop does not have string resistance, and the motor runs in characteristic curve 4, then the motor drives the constant torque load TL to run at point H and the motor speed is nH. When the need to reduce the speed of the drag system, KM1 off, KM2 closed, the resistor R1 string into the rotor circuit, the motor running in the curve characteristics 3, the motor becomes r2 + R1 mechanical properties, operation from the H point to the left translation, H1 The current I2 / decreases and the electromagnetic torque Tem decreases, so that Tem <TL, the motor decelerates and the slip s increases, resulting in a corresponding increase of the rotor emf sE2, which leads to the increase of the electron current I2 / and Tem to make the system reach a new stable point P , Back to Tem = TL again, but the rotational speed drops from nH to nP. Under the constant torque load, changing the closed state of KM1, KM2 and KM3, three mechanical characteristics can be obtained. The larger the series resistance is, the lower the rotational speed is.

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