High efficiency and energy saving of three-phase asynchronous motors have always been the continuous research and development guidelines of major high-efficiency motor manufacturers, and high-efficiency motors are directly related to national energy-saving and emission-reduction policies. Many national key projects and municipal projects bidding motors must be satisfied with IE3 energy efficiency The inspection requirements are particularly for motors imported into European countries through exports. These requirements are almost the lowest threshold.
However, for some motor manufacturers, it is too difficult to improve motor efficiency, and there are many bottlenecks to be broken, such as loss determination, key factors affecting motor efficiency, and the cause of loss and quantitative elucidation.
1. Large copper loss of motor stator
Stator winding resistance is large: (1) the wire resistivity is large or the wire diameter is small, the wire diameter is uneven or the number of parallel windings is small; (2) the wiring is wrong or the welding is not strong; (3) the actual number of turns is more than the design value.
The stator current is large: (1) Other losses are large; (2) The three phases are out of balance due to the difference in the stator windings; (3) The stator and rotor air gaps are seriously uneven; (4) The number of turns is less than the normal value. The resistance will be less than the normal value; (5) The winding wiring is incorrect.
2. Large copper loss of motor rotor
The resistance of the rotor winding (or bar) is large: (1) Aluminum (copper) has a large resistivity; (2) There are air holes or impurities in the cast aluminum rotor bar or end ring, or the forging defect causes local thinness Problems; (3) The stator slots are not neat (indicated as notch serrations), there are wrong pieces and reverse pieces, which cause the effective area of the rotor slot to be insufficient; (4) The aluminum structure is loose due to the improper selection of casting aluminum parameters, It directly leads to an increase in resistivity; (5) The material does not meet the requirements, such as the use of alloy aluminum for ordinary aluminum rotors; (6) The wrong rotor is used.
3. Large motor loss
The bearing or the bearing assembly quality is not good, at this time the bearing will have a serious fever or be unable to move. ● Wrong use of external fans (for example, 2-pole motors using 4-pole fans) or wrong blade angles; according to the general design, 2P motor fans are relatively small, and the method of reducing losses by adjusting the fan method is very effective, but the premise is The temperature rise function of the motor must be guaranteed.
The small diameter of the bearing chamber causes the outer ring of the bearing to be compressed and deformed, resulting in increased friction loss of the bearing; this environment may also cause the bearing to overheat and fail.