Since the loss distribution of the motor varies with the power size and the number of poles, in order to reduce the loss, we should focus on taking measures for the main loss components of different powers and pole numbers. Some ways to reduce the loss are briefly described as follows:

1. Increase effective materials to reduce winding loss and iron loss

According to the similarity principle of motors, when the electromagnetic load remains unchanged and the mechanical loss is not considered, the loss of the motor is approximately proportional to the cube of the linear size of the motor , and the input power of the motor is approximately proportional to the fourth power of the linear size. From this, the relationship between efficiency and effective material usage can be approximated. In order to obtain a larger space under certain installation size conditions so that more effective materials can be placed to improve the efficiency of the motor, the outer diameter size of the stator punching becomes an important factor. Within the same machine base range, American motors have greater output than European motors. In order to facilitate heat dissipation and reduce temperature rise, American motors generally use stator punchings with larger outer diameters, while European motors generally use stator punchings with smaller outer diameters due to the need for structural derivatives such as explosion-proof motors and to reduce the amount of copper used at the winding end and production costs.

2. Use better magnetic materials and process measures to reduce iron loss

The magnetic properties (magnetic permeability and unit iron loss) of the core material have a great influence on the efficiency and other performance of the motor. At the same time, the cost of the core material is the main part of the cost of the motor. Therefore, the selection of suitable magnetic materials is the key to designing and manufacturing high-efficiency motors. In higher-power motors, iron loss accounts for a considerable proportion of the total loss. Therefore, reducing the unit loss value of the core material will help reduce the iron loss of the motor. Due to the design and manufacturing of the motor, the iron loss of the motor greatly exceeds the value calculated according to the unit iron loss value provided by the steel mill. Therefore, the unit iron loss value is generally increased by 1.5~2 times during design to take into account the increase in iron loss.

The main reason for the increase in iron loss is that the unit iron loss value of the steel mill is obtained by testing the strip material sample according to the Epstein square circle method. However, the material is subjected to great stress after punching, shearing and laminating, and the loss will increase. In addition, the existence of the tooth slot causes air gaps, which leads to no-load losses on the surface of the core caused by the tooth harmonic magnetic field. These will lead to a significant increase in the iron loss of the motor after it is manufactured. Therefore, in addition to selecting magnetic materials with lower unit iron loss, it is necessary to control the lamination pressure and take necessary process measures to reduce iron loss. In view of price and process factors, high-grade silicon steel sheets and silicon steel sheets thinner than 0.5mm are not used much in the production of high-efficiency motors. Low-carbon silicon-free electrical steel sheets or low-silicon cold-rolled silicon steel sheets are generally used. Some manufacturers of small European motors have used silicon-free electrical steel sheets with a unit iron loss value of 6.5w/kg. In recent years, steel mills have launched Polycor420 electrical steel sheets with an average unit loss of 4.0w/kg, even lower than some low-silicon steel sheets. The material also has a higher magnetic permeability.

In recent years, Japan has developed a low-silicon cold-rolled steel sheet with a grade of 50RMA350, which has a small amount of aluminum and rare earth metals added to its composition, thereby maintaining a high magnetic permeability while reducing losses, and its unit iron loss value is 3.12w/kg. These are likely to provide a good material basis for the production and promotion of high-efficiency motors.

3. Reduce the size of the fan to reduce ventilation losses

For larger power 2-pole and 4-pole motors, wind friction accounts for a considerable proportion. For example, the wind friction of a 90kW 2-pole motor can reach about 30% of the total loss. Wind friction is mainly composed of the power consumed by the fan. Since the heat loss of high-efficiency motors is generally low, the cooling air volume can be reduced, and thus the ventilation power can also be reduced. The ventilation power is approximately proportional to the 4th to 5th power of the fan diameter. Therefore, if the temperature rise permits, reducing the fan size can effectively reduce wind friction. In addition, the reasonable design of the ventilation structure is also important for improving ventilation efficiency and reducing wind friction. Tests have shown that the wind friction of the high-power 2-pole part of a high-efficiency motor can be reduced by about 30% compared with ordinary motors. Since the ventilation loss is reduced significantly and does not require much additional cost, changing the fan design is often one of the main measures taken for this part of high-efficiency motors.

4. Reduce stray losses through design and process measures

The stray loss of asynchronous motors is mainly caused by high-frequency losses in the stator and rotor cores and windings caused by high-order harmonics of the magnetic field. To reduce the load stray loss, the amplitude of each phase harmonic can be reduced by using Y-Δ series-connected sinusoidal windings or other low-harmonic windings, thereby reducing the stray loss. Tests have shown that the use of sinusoidal windings can reduce stray losses by more than 30% on average.

5. Improve die-casting process to reduce rotor loss

By controlling the pressure, temperature and gas discharge path during the rotor aluminum casting process, the gas in the rotor bars can be reduced, thereby improving the conductivity and reducing the aluminum consumption of the rotor. In recent years, the United States has successfully developed copper rotor die-casting equipment and corresponding processes, and is currently conducting small-scale trial production. Calculations show that if copper rotors replace aluminum rotors, rotor losses can be reduced by about 38%.

6. Apply computer optimization design to reduce losses and improve efficiency

In addition to increasing materials, improving material performance and improving processes, computer optimization design is used to reasonably determine various parameters under the constraints of cost, performance, etc., so as to obtain the maximum possible improvement in efficiency. The use of optimization design can significantly shorten the time of motor design and improve the quality of motor design.

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Post time: Aug-12-2024