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Motor Repair Knowledge - Cooling Problems at Low Speed
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- Time of issue:2014-08-06 14:21
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[Summary information]Ordinary asynchronous motor inverter power supply, will make the electromagnetic, mechanical
Motor Repair Knowledge - Cooling Problems at Low Speed
(Summary description)Ordinary asynchronous motor inverter power supply, will make the electromagnetic, mechanical
- Categories:Industry News
- Author:
- Origin:
- Time of issue:2014-08-06 14:21
- Views:
Information
At present small and medium-sized frequency converter, many adopt PWM control mode. Its carrier frequency is about a few thousand to a dozen kilohertz, which makes the motor stator windings to withstand high voltage rise rate, equivalent to the imposition of a steep motor surge voltage, the motor turns to withstand more insulation Harsh test. In addition, the PWM chopper generated by the rectangular chopper impulse voltage superimposed on the motor operating voltage, the motor will pose a threat to the insulation, insulation to high voltage repeated impact will accelerate the aging.
Ordinary asynchronous motor inverter power supply, will make the electromagnetic, mechanical, ventilation and other factors caused by the vibration and noise become more complex. Various time harmonics contained in the variable frequency power supply interfere with the inherent space harmonics of the electromagnetic part of the motor to form various electromagnetic exciting forces. When the frequency of the electromagnetic force wave and the natural frequency of the motor body is the same or close to the resonance phenomenon will occur, thus increasing the noise. Due to the wide range of motor operating frequency, speed range, a variety of electromagnetic force wave frequency is difficult to avoid the inherent vibration frequency of the motor components.
Motor repair reveals cooling problems at low speeds. First of all, asynchronous motor impedance is not ideal, when the power supply frequency is low, the power caused by higher harmonics loss. Second, the normal asynchronous motor revolving speed decreases, the cooling air flow rate and the third power of the proportional decrease, causing the motor low-speed cooling conditions deteriorate, the temperature rise dramatically increased, it is difficult to achieve constant torque output.
High-order harmonics can cause stator copper loss, rotor copper loss, iron loss, and additional losses. The most significant motor is copper loss on the rotor. Because the asynchronous motor rotates at a synchronous speed corresponding to the frequency of the fundamental wave, a large rotor loss is generated when the harmonic voltage is cut at a large slip to the rotor bar.
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