Analysis of the additional loss of asynchronous motor load
Additional losses in asynchronous motor loads are usually not calculated in detail. In many countries, the standard specifies that the additional loss at load accounts for 0.5% of the motor output (generator) or input (motor) power. Of course this value is very rough. In a small asynchronous motor using a pressure cast aluminum process, the additional loss during load generally accounts for 2 to 3% of the output power, and even up to 4 to 5% or more. This not only seriously affects the operating economy and starting performance of the motor, but also may cause excessive line temperature rise. Therefore, over the years, how to accurately calculate and reduce the additional loss when the cage rotor asynchronous motor load has been paid attention to has been paid attention to.
Cage rotor asynchronous motor load additional loss
The additional losses when the cage rotor asynchronous motor is loaded mainly have the following parts:
• Additional losses in the stator winding's leakage magnetic field in the winding and in the metal parts near the winding ends.
• Additional losses due to induced currents in the squirrel-cage rotor windings due to the magnetic field generated by the stator magnetomotive harmonics.
● The surface loss caused by the magnetic field generated by the stator magnetic potential harmonics on the surface of the rotor core. Due to the demagnetization effect of the induced current in the squirrel-cage rotor winding, only a small amount of harmonic magnetic field can penetrate deep into the rotor tooth, so the pulse vibration loss generated by these harmonics in the tooth can be ignored. The additional losses generated by the rotor magnetomotive harmonics in the stator core are relatively small and are usually negligible.
● Loss due to leakage current in cast aluminum rotors without slot insulation.
In the above, the leakage magnetic field of the stator winding is generated by the fundamental frequency current in the winding and the metal component near the winding end, so it is also called the fundamental frequency addition (stray) loss. The rest are generated by high-frequency current, so it is also called high-frequency additional (stray) loss.
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