Selection Of High-efficiency Motor Silicon Steel Sheets

GNEE Silicon Steel Sheet

Motor loss distribution

At present, high-efficiency motors have become the mainstream in the development and application of small and medium-sized motors. In particular, industrialized countries such as Europe and the United States attach great importance to energy conservation and environmental protection. Development and applications of electric motors. In order to expand the international market share of electric motors, it has become a top priority for Chinese electric motor manufacturers to adopt new technologies, new processes, and new materials to improve the efficiency of electric motors as much as possible.

Since the loss distribution of a motor varies with power and number of poles, measures should be taken for the associated losses at different powers and number of poles. Among them, the selection of magnetically permeable materials is particularly important, which has a greater impact on the stator's copper loss, iron loss and other properties, and the cost of the iron core material is the main part of the motor cost. Therefore, selecting silicon steel sheets suitable for high-efficiency motors is the key to the design and manufacturing of high-efficiency motors, and should be selected carefully.

Through comparative analysis of the electromagnetic properties of silicon steel sheets for motors, the selection and application of silicon steel sheets for high-efficiency motors were studied and discussed. Through experiments and data analysis, the selection principles for silicon steel sheets for high-efficiency motors were proposed. Core materials are provided for motor selection for reference.

Introduction to silicon steel sheets

Silicon steel sheets are also called electrical steel sheets. Adding a small amount of silicon to iron can increase the resistivity of the material, significantly improve magnetic aging, increase the brittleness of the material, and reduce the magnetic induction intensity. Therefore, the limit of silicon is 4.5%. Silicon steel sheets are mainly used for power frequency AC electromagnetic devices, such as transformers, motors, transformer switches and relay cores. In our country, silicon steel sheets are traditionally divided into hot-rolled silicon steel sheets and cold-rolled silicon steel sheets, but in today's world, silicon steel sheets are mostly divided into non-oriented silicon steel sheets and grain-oriented silicon steel sheets based on grain orientation.

Hot-rolled silicon steel sheet is a magnetic non-oriented silicon steel sheet, which is a ferrosilicon alloy. Compared with cold-rolled sheets, it has the characteristics of good material stability, much lower punching stress than cold-rolled sheets, small specific gravity, and large difference between the same sheets. Cold-rolled sheet is a low-silicon and low-carbon alloy with the characteristics of small iron loss, high magnetic induction, smooth surface, uniform thickness, and small difference between the same sheets. The use of silicon steel sheets in motor cores instead of carbon steel plates and pure iron is a huge progress in history. Low-loss silicon steel sheets improve motor performance and reduce motor size.

Nowadays, silicon-free steel sheets are used in small motor cores instead of silicon steel sheets, because the silicon-free steel sheets smelted by modern technology are different from the original low-carbon steel sheets. It not only has high magnetic induction intensity, but also has iron loss similar to silicon steel sheets. Whether it is cold-rolled silicon steel sheet or silicon-free steel sheet, its magnetic induction and loss are very sensitive to mechanical stress. Therefore, how to restore the original magnetic permeability and iron loss after punching is an issue that should be considered when selecting silicon steel sheets.

Selection of high-efficiency motor silicon steel sheets

The selection of high-efficiency motor silicon steel sheets must not only pursue high grade and low iron loss, but also must be comprehensively considered. Although the higher the grade, the lower the iron loss, but the magnetic permeability will be relatively poor, which is especially important for small motors. .In a 5kW motor, since reactive current accounts for a large proportion of the stator current, the no-load current (mainly magnetizing current) accounts for a considerable proportion of the full-load current, reaching about 70%. As the power increases, the proportion of no-load current to full-load current gradually decreases.

Therefore, for motors with smaller power, the stator copper loss accounts for a large proportion of the total loss. First, electrical steel sheets with good magnetic permeability should be used as the stator core. This can greatly reduce the excitation current and significantly improve the iron loss and stator. iron core. Copper consumption.

For high-power motors, since the proportion of no-load current to full-load current is very small, the iron loss already accounts for a considerable proportion of the total loss. The use of high magnetic permeability silicon steel sheets is not obvious for improving efficiency, so reducing the unit loss of the core material will help reduce iron losses.

Due to the design and manufacture of the motor, the iron loss in the motor test greatly exceeds the value calculated based on the unit iron loss value provided by the steel mill. However, after the material is punched, sheared and laminated, it will be subject to greater stress, which will worsen the magnetic permeability of the punched plate and increase iron loss. In addition, due to the existence of cogging, the harmonic magnetic field of the air gap teeth is on the core surface. The high-frequency loss caused by no-load will lead to a significant increase in iron loss after the motor is produced. Therefore, in addition to selecting magnetic materials with lower unit iron loss, it is also necessary to control the lamination pressure and take necessary process measures to reduce iron loss.

This grade of silicon steel sheet has high silicon carbon content, low density, light weight, good material stability, basically no expiration date, and the punching stress is much less than that of cold-rolled sheet. As can be seen from Table 1, its low-field magnetism is not very good, but it is enough for high-efficiency motors, because the stator flux density of high-efficiency motors is between 1.0T and 1.5T, and the rotor flux density is between 1.0T and 1.0T. to 1.0T. Between 1.6T.

If cold-rolled sheets are used, in order to give full play to their advantages, the mechanical stress after punching and shearing must be resolved. There are many theoretical methods to solve the punching shear stress of cold-rolled sheets, and the most effective method is to choose a reasonable annealing process. However, due to limitations of equipment and process parameters, this process has not yet been promoted in China. This process is only used for small motors.

Based on the theoretical introduction and test parameters of other motor manufacturers, combined with home appliance export products, we also conducted a simulation attempt of this process. Due to equipment limitations, we just put the punched silicon steel sheets into the heating furnace and kept them at 500°C for 2 hours. The results show that the magnetic permeability of the silicon steel sheet recovers better after annealing, and the iron loss is significantly improved.

Factors that determine the efficiency of high-efficiency motors

The degree of realization of high motor efficiency is closely related to the selection of raw materials, especially magnetic materials. High-efficiency motors mainly focus on how to reduce various losses. The degree of deviation between the design values and test values of iron losses, stator copper losses, rotor copper losses, and stray losses depends entirely on the selection of silicon steel sheets and iron cores. Build quality.