What are the factors that affect the high efficiency of three-phase asynchronous motors?

Update:10 Oct 2020
Summary:

A key factor affecting the high efficiency of three-pha […]

A key factor affecting the high efficiency of three-phase asynchronous motors.

1. Large copper loss of motor stator

Large stator winding resistance:

(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) Incorrect wiring or weak welding;

(3) The actual number of turns is more than the design value.

Large stator current:

(1) Other losses are large;

(2) The three-phase is unbalanced due to the asymmetry of the stator winding;

(3) The air gap of the stator and rotor is seriously uneven;

(4) Because the number of turns is less than the normal value, the resistance will be less than the normal value at this time;

(5) The winding wiring is incorrect.

2. Large copper loss of motor rotor

The resistance of the rotor winding (or bar) is large:

(1) The resistivity of aluminum (copper) is relatively large;

(2) There are air holes or impurities in the cast aluminum rotor guide bar or end ring, or local thinness problems caused by casting defects;

(3) The stator slots are not neat (shown as notch serrations), there are wrong pieces and reverse pieces, resulting in insufficient effective area of the rotor slots;

(4) Due to improper selection of cast aluminum parameters, the structure of aluminum is loosened, which directly leads to an increase in resistivity;

(5) The material does not meet the requirements, for example, the ordinary aluminum rotor uses alloy aluminum;

(6) Use the wrong rotor, etc.

3. Large mechanical loss of the motor

If the quality of the bearing or the bearing assembly is not good, the bearing will become severely heated or rotate inflexibly.

The external fan is used incorrectly (for example, a 4-pole fan is used in a 2-pole motor) or the angle of the fan blade is wrong; according to the conventional design, the 2P motor fan is relatively small, and the method of reducing loss by adjusting the fan is very effective, but the premise is to ensure The temperature rise performance of the motor.

The small diameter of the bearing chamber causes the outer ring of the bearing to be compressed and deformed, resulting in increased bearing friction loss; this situation may also cause the bearing to overheat and fail.

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