High-efficiency motors are directly linked to energy conservation and emission reduction policies. Motors for bidding in many national key projects and municipal projects must meet the IE3 energy efficiency assessment requirements, especially for motors exported to European countries, where these requirements are almost the minimum threshold.
However, for motor manufacturers, improving efficiency is extremely difficult, with many bottleneck technologies needing to be overcome, such as loss measurement, determination of key factors affecting motor efficiency, and quantitative analysis of the causes of loss. Below , MS will begin by discussing the causes of increased loss, breaking them down and analyzing them one by one.
Large stator copper loss
● High stator winding resistance: (1) High conductor resistivity or small wire diameter, uneven wire diameter or few parallel windings; (2) Incorrect wiring or poor welding; (3) The actual number of turns is more than the design value.
●Large stator current: (1) Other losses are large; (2) The three phases are unbalanced due to the asymmetry of the stator winding; (3) The air gap between the stator and rotor is seriously uneven; (4) The resistance will be less than the normal value because the number of turns is less than the normal value; (5) The winding connection is incorrect.
High rotor copper loss
● High resistance of rotor winding (or conductor): (1) The resistivity of aluminum (copper) is relatively high; (2) There is air, pores or impurities in the conductor or end ring of the cast aluminum rotor, or there is a problem of thin strips in some areas due to casting defects; (3) The stator slots are not neat (manifested as serrated slot openings), with misaligned or reversed pieces, resulting in insufficient effective area of rotor slots; (4) The aluminum structure is loose due to improper selection of casting aluminum parameters, which directly leads to an increase in resistivity; (5) The material does not meet the requirements, such as using alloy aluminum in ordinary aluminum rotors; (6) The wrong rotor is used, etc.
● The rotor current is large; (1) the wrong rotor is used; (2) the wrong aluminum is used when casting aluminum, such as using ordinary aluminum in an alloy aluminum rotor; (3) the rotor core is not properly stacked, resulting in a large area of aluminum entering between the laminations, which leads to excessive lateral current in the rotor.
Large stray loss
●Inappropriate selection of stator winding type or pitch;
● Improper selection of stator and rotor slot matching;
● The air gap is too small or severely uneven;
●The rotor bars are severely short-circuited to the core;
● The stator winding ends are too long, etc.
Large iron loss
●Poor quality silicon steel sheets or incorrect material usage, such as using 800 grade instead of 600 grade steel; motor manufacturers that purchase iron cores from external suppliers should pay special attention to this issue.
● Poor insulation between stator core laminations: (1) No insulation treatment or poor treatment effect; (2) Excessive pressure during core stacking, which damages the insulation between laminations; (3) Short circuit between core laminations when machining the stator inner bore or filing the core (this problem exists in most core manufacturing plants).
● Insufficient number of core sheets and insufficient iron weight: (1) Insufficient number of sheets (missing sheets); (2) Low stacking pressure and insufficient compaction, resulting in insufficient iron weight; (3) Large burrs on the stamped sheets, and the iron weight cannot be guaranteed when the iron length is in line; (4) Excessive paint coating, which is a direct quality problem of silicon steel sheets.
● When the magnetic circuit is oversaturated, the curve of the relationship between the no-load current and the voltage becomes severely distorted.
●The no-load stray loss is relatively large because it is included in the iron loss during the test, making the iron loss appear larger.
● Removing the windings by burning or heating with electricity can cause the core to overheat, leading to a decrease in magnetic conductivity and damage to the inter-laminar insulation. This problem mainly occurs when the windings are removed by burning after a fault; some motor manufacturers have found a way to remove the windings by soaking them in an alkaline solution.
High mechanical wear
● Poor bearing quality or bearing assembly will cause the bearing to overheat or rotate inflexibly.
● The external fan is used incorrectly (e.g., a 4-pole fan is used for a 2-pole motor) or the fan blade angle is incorrect; according to conventional design, the fan of a 2P motor is relatively small. Adjusting the fan is a very effective way to reduce losses, but the premise is to ensure the motor's temperature rise performance.
●The base and the bearing housings at both ends are not coaxial;
● A small bearing housing diameter causes the outer ring of the bearing to deform under pressure, resulting in increased bearing friction loss; this situation may also lead to bearing overheating and failure.
● Excessive grease or poor-quality grease in the bearing housing. This problem is particularly noticeable in high-voltage motors. Ms. Can once conducted an experiment where the highest temperature point of the bearing cover was 10K higher than the lowest point. Upon inspection, it was found that there was indeed a significant accumulation of grease in that location.
● Stator-rotor rubbing, also known as rotor rubbing, does not directly cause the motor to stop turning, but it significantly increases motor losses.
● Incorrect rotor axial dimensions cause the two ends to jam, making rotation inflexible.
● Improper installation or deformation of components such as oil seals or water-slinging rings can generate significant frictional resistance.
● The fan motor rubs against the connecting parts, causing it to rotate poorly.
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