When the voltage is reduced, the motor, as the core device of an electric drive, undergoes a series of significant changes. The following is a detailed analysis of these changes, designed to help better understand the impact of voltage reduction on motor performance and operating conditions.
一、Current Changes
Explanation of the principle: According to Ohm’s law, the relationship between current I, voltage U and resistance R is I=U/R. In electric motors, the resistance R (mainly stator resistance and rotor resistance) usually does not change much, so the reduction of voltage U will directly lead to an increase in current I. For different types of electric motors, the current change will be the same as that of stator resistance. For different types of motors, the specific manifestations of current changes may vary.
Specific performance:
DC motors: brushless DC motors (BLDC) and brushed DC motors experience a significant increase in current when the voltage is reduced if the load remains constant. This is because the motor requires more current to maintain the original torque output.
AC motors: For asynchronous motors, although the motor automatically reduces its speed to match the load when the voltage is reduced, the current may still rise in the case of a heavier or more rapidly changing load. As for synchronous motor, if the load remains unchanged when the voltage is lowered, the current will not change much theoretically, but if the load increases, the current will increase as well.
二、torque and speed change
Change of torque: Voltage reduction usually leads to the reduction of motor torque. This is because torque is proportional to the product of current and flux, and when the voltage is lowered, although the current increases, the flux may decrease due to the lack of voltage, resulting in a decrease in overall torque. However, in some cases, such as in DC motors, if the current is increased sufficiently, it may compensate for the decrease in flux to some extent, keeping the torque relatively stable.
Speed change: For AC motors, especially asynchronous and synchronous motors, a reduction in voltage will directly result in a reduction in speed. This is because the speed of the motor is related to the frequency of the power supply and the number of motor pole pairs, and the reduction of voltage will affect the strength of the motor’s electromagnetic field, which in turn reduces the speed. For DC motors, the speed is proportional to the voltage, so the speed will decrease accordingly when the voltage decreases.
三、efficiency and heat
Lower efficiency: lower voltage will lead to lower motor efficiency. Because the motor in the lower voltage operation, need more current to maintain the output power, and the increase in current will increase the motor’s copper loss and iron loss, thus reducing the overall efficiency.
Increased heat generation: Due to increased current and decreased efficiency, motors generate more heat during operation. This not only accelerates the aging and wear of the motor, but also may trigger the activation of the overheating protection device, resulting in motor shutdown.
四、 the impact on the life of the motor
Long-term operation under unstable voltage or low voltage environment will seriously shorten the service life of the motor. Because the voltage reduction caused by the increase in current, torque fluctuations, speed drop and efficiency reduction and other issues will cause damage to the internal structure and electrical performance of the motor. In addition, the increase in heat generation will also accelerate the aging process of the motor insulation material.
五、Countermeasures
In order to reduce the impact of voltage reduction on the motor, the following measures can be taken:
Optimize the power supply system: ensure that the voltage of the power supply grid is stable, to avoid the impact of voltage fluctuations on the motor.
Selection of suitable motors: in the design and selection of voltage fluctuations take into full account the factors of selection of motors with a wide range of voltage adaptation.
Install voltage stabilizer: install voltage stabilizer or voltage regulator at the input of motor to maintain the stability of voltage.
Strengthen the maintenance: regular inspection and maintenance of the motor to detect and deal with potential problems in a timely manner in order to extend the service life of the motor.
In summary, the impact of voltage reduction on the motor is multi-faceted, including current changes, torque and speed changes, efficiency and heat problems and the impact of motor life. Therefore, in practical applications need to take effective measures to reduce these effects to ensure the safe and stable operation of the motor.
Post time: Aug-08-2024