Jiangyou Inverter used to affect your three-phase asynchronous motor like this

Hello, Welcome to Ever Power!

Industry news

Jiangyou Inverter used to affect your three-phase asynchronous motor like this

author:xiaoE date:2020-01-05 12: 47

　　Ordinary three-phase asynchronous motorIt is impossible to be completely accustomed to the requirements of variable frequency speed regulation, because they are planned according to the constant frequency 50hz/60hz.The frequency converter once affected the three-phase asynchronous motor in this way, did you know?

　　Harmonic electromagnetic noise and sensation

　　The harmonics of each time contained in the variable frequency power supply interfere with the inherent spatial harmonics of the electromagnetic part of the motor to form various electromagnetic exciting forces.When an asynchronous motor is powered by a frequency converter, the sensation and noise caused by electromagnetic, mechanical, ventilation and other factors will become more and more messy.

　　Because the motor has a wide operating frequency and a large change in speed, it is difficult for the frequencies of various electromagnetic waves to avoid the inherent sensational frequencies of the various components of the motor.When the frequency of the electromagnetic force wave is consistent with or close to the natural oscillation frequency of the motor body, resonance will occur, and then the noise will be increased.

　　Motor power and temperature rise

　　Regardless of which method of frequency converter, different degrees of harmonic voltage and current are generated during operation, making the motor run under non-sinusoidal voltage and current.

　　Take the sine wave PWM type frequency converter that is now widely used as an example, its low-order harmonics are basically zero, and the remaining high-order harmonic components that are about twice as large as the carrier frequency are: 2u+1 (u is the modulation ratio) .High-order harmonics will cause the addition of stator copper loss, rotor copper (aluminum) loss, iron loss and additional loss, the most significant is the rotor copper (aluminum) loss.

　　Because the asynchronous motor rotates at a synchronous speed close to the fundamental frequency, after the high-order harmonic voltage cuts the rotor bar with a large slip, a large rotor loss will occur.

　　In addition, the additional copper loss due to the skin effect needs to be considered.These losses will cause the rated heating of the motor, the power drop, and the output power decrease.Ordinary three-phase asynchronous motorUnder the condition of non-sinusoidal power supply output by the inverter, the temperature rise is generally increased by 10%-20%.

　　Motor insulation strength

　　Nowadays, many small and medium-sized inverters adopt PWM control methods.The carrier frequency is about several thousand to ten kilohertz, which makes the motor stator winding to withstand a high rate of voltage rise, which is equivalent to imposing a steep impulse voltage on the motor, making the motor’s turn-to-turn insulation to withstand relatively strict Detection.

　　In addition, the rectangular chopping impulse voltage generated by the PWM inverter is superimposed on the motor operating voltage, which will pose a threat to the motor's ground insulation, and the ground insulation will accelerate its aging under the repeated impact of high voltage.

　　Cooling at low speed

　　The impedance of the asynchronous motor is not ideal. When the frequency of the power supply is lower, the loss caused by the higher harmonics in the power supply is larger.

　　Generally, when the rotation speed of an asynchronous motor decreases, the cooling air volume decreases in proportion to the third power of the rotation speed, which makes the low-speed cooling condition of the motor deteriorate, and the temperature rise sharply increases, making it difficult to achieve constant torque output.

　　The motor's habitual force for frequent starting and braking

　　After the frequency converter is used for power supply, the motor can be started at a very low frequency and voltage with no inrush current, and various braking methods provided by the frequency converter can be used for rapid braking, in order to achieve frequent starting and braking inventions Condition.Therefore, the mechanical system and electromagnetic system of the motor are under the action of cyclic alternating force, which brings fatigue and accelerated aging to the mechanical structure and the insulating structure.

　　