Analysis of the causes of low motor efficiency
High-efficiency motors are directly related to energy-saving and emission-reduction policies. Many national key projects and municipal projects must meet the IE3 energy efficiency assessment requirements, especially for motors that are exported to European countries. These requirements are almost the lowest threshold.
However, for motor manufacturers, the efficiency improvement is too difficult. There are many bottleneck technologies to be broken, such as the determination of loss, the determination of key factors affecting motor efficiency, the cause of loss and quantitative analysis. The following MS. First from the cause of the increase in loss, decomposition and analysis one by one.
Large stator copper loss
●The stator winding resistance is large: (1) The wire has high resistivity or small wire diameter, the wire diameter is not uniform or the number of 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-phase unbalance due to the asymmetry of the stator windings; (3) the air gap of the stator is severely uneven; (4) because 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.
Large rotor copper loss
● Rotor winding (or bar) resistance is large: (1) aluminum (copper) has a high resistivity; (2) cast aluminum rotor bar or end ring has gas pores or impurities, or localized due to casting defects Thin strip problem; (3) the stator slot is not neat (expressed as slotted serration), there are wrong pieces and reverse pieces, resulting in insufficient effective area of the rotor slot; (4) due to improper selection of cast aluminum parameters, the microstructure of the aluminum is loose, directly Lead to increase in resistivity; (5) materials do not meet the requirements, such as ordinary aluminum rotor using alloy aluminum; (6) using the wrong rotor.
●The rotor current is large; (1) the wrong rotor is used; (2) the wrong aluminum is used for casting aluminum, for example, the aluminum alloy rotor uses ordinary aluminum; (3) the rotor core is not laminated, resulting in a large area of aluminum between the sheets. This causes the lateral current of the rotor to be too large.
Large stray loss
● improper selection of stator winding type or pitch;
● improper selection of rotor and groove grooves;
●The air gap is too small or severely uneven;
● The rotor bar and the core are severely short-circuited;
● The stator winding ends are too long.
Large iron loss
●The quality of silicon steel sheet is poor or the material is used incorrectly. For example, the 600 material misuse is used as the depreciation number of 800; the motor factory for the purchased iron core should pay special attention to this problem.
●Insulation between the stator core sheets is not good: (1) The insulation treatment is not performed or the treatment effect is not good; (2) The pressure is too large when the core is laminated, so that the insulation between the sheets is damaged; (3) The inner stator of the vehicle is repaired or repaired. When the iron core is used, it causes a short circuit between the core piece and the piece (this problem exists in most iron core manufacturing plants).
●The number of core pieces is insufficient, and the iron weight is not enough: (1) the number of chips is insufficient (missing pieces); (2) the pressure of lamination is small, not compacted, and the direct result is insufficient iron weight; (3) the burr is larger When the iron length is met, the iron weight cannot be guaranteed; (4) the paint is too thick, which is a direct quality problem of the silicon steel sheet.
● The magnetic circuit is too saturated, and the relationship between the no-load current and the voltage is bent more severely.
● The no-load stray loss is large, and it is included in the iron loss during the test, which makes the iron loss appear larger.
●When the winding is removed by fire or electric heating, the core is overheated, and the magnetic permeability is deteriorated and the insulation between the sheets is damaged. This problem mainly occurs when the winding is taken out by the method of fire after the winding failure; some motor manufacturers have sought a way to take out the winding by the immersion method.
High mechanical loss
● The bearing or bearing assembly quality is not good, at this time the bearing will be severely heated or the rotation is not flexible.
●The external fan is wrong (for example, the 2-pole motor uses a 4-pole fan) or the fan blade angle is incorrect. According to the conventional design, the 2P motor fan is relatively small. The method of reducing the loss by adjusting the fan method is very effective, but the premise is Guarantee the temperature rise performance of the motor.
● different axes of the bearing seat and the bearing housing at both ends;
● The bearing chamber has a small diameter, which causes the outer ring of the bearing to be deformed under pressure, resulting in increased bearing friction loss; this situation may also cause the bearing to overheat.
●The grease in the bearing chamber is too much or the quality of the grease is not good. This problem is obvious on high-voltage motors. Ms. has done a test. The highest point of the bearing cap temperature is 10K higher than the lowest point. When the inspection is turned on, the grease at this position does accumulate more.
● Fixed rotor rubbing, which is what we call the broom, when the rotor is wiped, it will not directly lead to the motor not turning, but the motor loss increases obviously.
● The axial dimension of the rotor is incorrect, causing the two ends to die, making the rotation inflexible.
● Components such as oil seals or water ring are not properly installed or deformed, resulting in large frictional resistance.
●With fan motor, the fan and the related parts are rubbed to cause poor rotation.
