The development of motors promotes social development and brings great convenience to people's lives. So how to improve the efficiency of motors and make motors better serve human beings? Below is the author of AIP to share with you.
High-efficiency motors are directly related to energy conservation and emission reduction policies. Many national key projects and municipal project bidding motors must meet the IE3 energy efficiency assessment requirements, especially those imported into European countries through export. These requirements are almost the minimum threshold.
However, for motor manufacturers, it is too difficult to improve efficiency, and there are many bottleneck technologies to be broken through, such as loss measurement, determination of key factors affecting motor efficiency, loss causes and quantitative analysis, etc. Let's start with the causes of increased loss, and then decompose and analyze them one by one.
Large stator copper loss
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. Wrong wiring or weak soldering
3. The actual number of turns is more than the design value.
Large stator current
(1) Other losses are larger;
(2) Three-phase unbalance due to stator winding asymmetry;
(3) The air gap between 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- Rotor copper loss is large
Rotor winding (or bar) resistance is large:
(1) The resistivity of aluminum (copper) is relatively large;
(2) There are air holes or impurities in the cast aluminum rotor bar or end ring, or there are local thin strip problems due to casting defects;
(3) The stator slots are not neat (shown as notch serrations), and there are staggered and reversed pieces, resulting in the insufficient effective area of the rotor slots;
(4) Due to improper selection of cast aluminum parameters, the organization of aluminum is loose, 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.
● Large rotor current;
(1) Use the wrong rotor;
(2) Wrong aluminum is used when casting aluminum, for example, ordinary aluminum is used for the alloy aluminum rotor;
(3) The lamination of the rotor core is not solid, resulting in a large area of aluminum entering between the sheets, resulting in excessive rotor transverse current.
3- Large stray loss
● Improper selection of stator winding type or pitch;
● Improper selection of stator and rotor slots;
● The air gap is too small or seriously uneven;
● The rotor bar and the iron core are seriously short-circuited;
● The end of the stator winding is too long, etc.
4-Large iron loss
The quality of the silicon steel sheet is poor or the material is used incorrectly. For example, the 600 material is mistakenly used for 800. This problem should be paid special attention to the motor factory that purchases the iron core.
● Poor insulation between stator core sheets:
(1) The insulation treatment is not carried out or the treatment effect is not good;
(2) When the iron core is stacked, the pressure is too large, so the insulation between the sheets is damaged;
(3) When the inner bore of the stator is turned or the iron core is repaired, the iron core piece and the piece are short-circuited (this problem exists in most iron core manufacturers).
● Insufficient number of iron core pieces and insufficient iron weight:
(1) Insufficient number of chips (missing chips);
(2) The stacking pressure is small and not compacted, and the direct result is insufficient iron weight;
(3) The punching burr is large, and the iron weight cannot be guaranteed when the iron length matches;
(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 curve of the relationship between no-load current and voltage is seriously curved.
● The no-load stray loss is large because it is included in the iron loss during the test, which makes the iron loss appear large.
● When the winding is dismantled by fire or electric heating, the iron core will be overheated, the magnetic permeability will be lowered, and the insulation between the chips will be damaged. This problem mainly occurs when the winding is removed by burning after the winding fails; some motor manufacturers have sought a way to remove the winding by lye soaking.
5- Large mechanical loss
● The quality of the bearing or bearing assembly is not good. At this time, the bearing will heat up seriously or rotate inflexibly.
● The external fan is wrongly used (for example, a 2-pole motor uses a 4-pole fan) or the angle of the fan blades is wrong; according to the conventional design, the 2P motor fan is relatively small, and the method of reducing the loss by adjusting the fan method is very effective, but the premise is Ensure the temperature rise performance of the motor.
● The machine base and the bearing chambers of the two end caps are not coaxial;
● The small diameter of the bearing chamber causes the outer ring of the bearing to be deformed under pressure, which increases the friction loss of the bearing; this situation may also cause the bearing to overheat and fail.
● Too much grease or poor quality grease is added to the bearing chamber. This problem is obvious in high-voltage motors. An experiment was done. The highest point of the bearing cap temperature is 10K higher than the lowest point. Open and check, and there is indeed a lot of grease in this position.
● The stator and rotor are rubbed, which is what we call sweeping. When t
● The axial dimension of the rotor is incorrect, causing the two ends to be stuck and making the rotation inflexible.
he stator and rotor are rubbed, it will not directly cause the motor not to rotate, but the motor loss will increase significantly.
● The oil seal or water-throwing ring and other components are installed incorrectly or deformed, resulting in greater frictional resistance.
● With a fan motor, the fan is rubbed against the related parts and the rotation is not smooth.
The efficiency of the motor is mainly determined during the design and selection. For example, the efficiency of the permanent magnet synchronous motor is higher than that of the AC asynchronous motor. It needs high-efficiency work. You need to choose a servo control system instead of a variable frequency speed regulation system. Of course, the cost is spent There is more money, so efficiency is closely related to cost.
To improve the efficiency of the motor, the essence is to reduce the loss of the motor. The loss of the motor is divided into mechanical loss and electromagnetic loss. For example, for an AC asynchronous motor, the current passes through the stator and rotor windings, which will produce copper loss and conductor loss, while the magnetic field in the iron It will cause eddy currents to bring about hysteresis loss, high harmonics of the air magnetic field will generate stray losses on the load, and there will be wear losses during the rotation of bearings and fans.
To reduce the loss of the rotor, you can reduce the resistance of the rotor winding, use a relatively thick wire with low resistivity, or increase the cross-sectional area of the rotor slot. Of course, the material is very important. Conditional production of copper rotors will reduce the loss by 15%. Left and right, the current asynchronous motors are basically aluminum rotors, so the efficiency is not so high.
Similarly, there is copper loss on the stator, which can increase the slot face of the stator, increase the full slot ratio of the stator slot, and shorten the end length of the stator winding. If a permanent magnet is used to replace the stator winding, there is no need to pass current. Of course, the efficiency can be obviously improved, which is the fundamental reason why the synchronous motor is more efficient than the asynchronous motor.
For the iron loss of the motor, high-quality silicon steel sheets can be used to reduce the loss on the hysteresis, or the length of the iron core can be lengthened, which can reduce the magnetic flux density, and can also increase the insulating coating. In addition, the heat treatment process is also critical.
The ventilation performance of the motor is more important. When the temperature is high, the loss will of course be large. The corresponding cooling structure or additional cooling method can be used to reduce friction loss.
High-order harmonics will produce stray losses in the winding and iron core, which can improve the stator winding and reduce the generation of high-order harmonics. Insulation treatment can also be performed on the surface of the rotor slot, and magnetic slot mud can be used to reduce the magnetic slot effect.
Extended reading: How to define a high-efficiency motor?
Ordinary motor: The motor is a device that converts electrical energy into mechanical energy. 70%-95% of the electrical energy absorbed by the motor is converted into mechanical energy. This is the efficiency value of the motor, which is an important technical indicator of the motor. The remaining 30%- The 5% part is consumed by the motor itself due to heat generation, mechanical loss, etc., so this part of the electric energy is wasted.
High-efficiency motor: A motor with a high power utilization rate is called a high-efficiency motor, or "high-efficiency motor" for short.
For ordinary motors, it is not easy to increase the efficiency by 1%, and the material will increase a lot, and when the motor efficiency reaches a certain value, no matter how much material is added, it cannot be improved. Most of the high-efficiency motors on the market are replacement products of three-phase asynchronous motors, which means that the basic working principle has not changed.
High-efficiency motors mainly improve the efficiency of motors through the following ways:
1. Increase the outer diameter of the iron core, increase the length of the iron core, increase the size of the stator slot, and increase the weight of the copper wire to achieve the purpose of improving efficiency. For example, the outer diameter of the Y2-8024 motor is increased from the current Φ120 to Φ130. The increase of Φ145, while increasing the length from 70 to 90. The amount of iron used for each motor increases by 3 kg. The copper wire increases by 0.9 kg.
2. Silicon steel sheets with good magnetic permeability are used. In the past, hot-rolled sheets with large iron loss were used, and high-quality cold-rolled sheets with low losses are now used, such as DW470. Even lower than the DW270.
3. Improve machining accuracy and reduce mechanical losses. Replace small fans to reduce fan losses. High-efficiency bearings are used.
4. Optimize the electrical performance parameters of the motor, and optimize the parameters by changing the slot shape.
5. Adopt cast copper rotor (complex process and high cost).
Therefore, to make a real high-efficiency motor, the design, raw materials, and processing costs are much higher, so that electricity can be converted into mechanical energy to the greatest extent.
Energy-saving measures for high-efficiency motors
Motor energy saving is a systematic project involving the entire life cycle of the motor. From the design and manufacture of the motor to the selection, operation, adjustment, maintenance, and scrapping of the motor, the effect of its energy-saving measures should be considered throughout the entire life cycle of the motor. In this aspect, the main consideration is to improve the efficiency from the following aspects.
The design of an energy-saving motor refers to the use of modern design methods such as optimization design technology, new material technology, control technology, integration technology, test and detection technology, etc., to reduce the power loss of the motor, improve the efficiency of the motor, and design an efficient motor.
When the motor converts electrical energy into mechanical energy, it also loses a part of the energy itself. Typical AC motor losses can generally be divided into three parts: fixed loss, variable loss, and stray loss. Variable losses are load-dependent and include stator resistance losses (copper losses), rotor resistance losses, and brush resistance losses; fixed losses are load-independent and include core losses and mechanical losses. The iron loss is composed of hysteresis loss and eddy current loss, which is proportional to the square of the voltage, and the hysteresis loss is also inversely proportional to the frequency; other stray losses are mechanical losses and other losses, including friction losses of bearings and fans, rotors and other windage losses due to rotation.
Features of high-efficiency motors
1. Save energy and reduce long-term operating costs. It is very suitable for textiles, fans, pumps, and compressors. The cost of motor purchase can be recovered by saving electricity for one year;
2. Direct start or speed regulation with a frequency converter can fully replace the asynchronous motor;
3. The rare earth permanent magnet high-efficiency energy-saving motor itself can save more than 15℅ of electric energy than ordinary motors;
4. The power factor of the motor is close to 1, which improves the quality factor of the power grid without adding a power factor compensator;
5. The motor current is small, which saves the transmission and distribution capacity and prolongs the overall operating life of the system;
6. Power saving budget: Take a 55Kw motor as an example, a high-efficiency motor saves 15% of electricity than a general motor, and the electricity fee is calculated at 0.5 yuan per kilowatt-hour. The cost of replacing the motor can be recovered by saving electricity within one year of using the energy-saving motor.
AIP focuses on global motor testing, takes user needs as the guide, puts quality first, strives for perfection, and continuously improves product quality. In the future, AIP will continue to develop new technologies for motor testing, develop new products, continuously improve the technical strength of its own products, and give back to our customers with better products and sincere services!
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