Analysis of factors affecting basic iron loss We first need to know some basic theories, which will help us understand. First of all, we need to know two concepts. One is alternating magnetization, which is simply what happens in the iron core of the transformer and the stator or rotor teeth of the motor; the other is the nature of rotating magnetization, which is produced by the stator or rotor yoke of the motor. There are many articles that start from two points and calculate the iron loss of the motor according to different characteristics in the above-mentioned solution method. Experiments show that the following phenomena exist in silicon steel sheets under two types of magnetization:
When the magnetic flux density is below 1.7 Tesla, the hysteresis loss caused by rotating magnetization is greater than that caused by alternating magnetization; when it is higher than 1.7 Tesla, the opposite is true. The magnetic flux density of the motor yoke is generally 1.0 to 1.5 Tesla, and the corresponding rotating magnetization hysteresis loss is about 45 to 65% greater than the alternating magnetization hysteresis loss.
Of course, the above conclusions are also taken, and I have not actually verified them. In addition, when the magnetic field in the iron core changes, a current will be induced in it, which is called eddy current, and the loss caused by it is called eddy current loss. In order to reduce eddy current loss, the motor core is usually not made of a whole piece, but is made of insulated steel sheets stacked axially to hinder the flow of eddy current. The specific iron loss calculation formula will not be repeated here. If you search Baidu for the basic formula and meaning of iron loss calculation, you will understand it clearly. The following analyzes several key points that affect our iron loss, so that you can forward or reverse the problem in actual engineering applications.
After talking about the above, let's talk about why the manufacturing of punching sheets affects iron loss? The punching process characteristics are mainly determined according to the different shapes of punching machines, according to the requirements of different types of holes and slots, and the corresponding shear mode and stress level are determined to ensure the conditions of the shallow stress area outside the lamination. Because of the relationship between depth and shape, it is often affected by sharp angles, so that high stress levels will cause great iron loss in the shallow stress area, especially in the part with relatively long shear edges within the lamination range. Specifically, it mainly appears in the tooth groove area, so in the actual research process, it often becomes the focus of research. Low-loss silicon steel sheets are often determined by larger grain sizes. The impact will cause synthetic burrs and tear shear at the bottom of the punching sheet, and the angle of the impact will have a significant impact on the burr size and deformation area. If a high stress area extends along the edge deformation zone to the inside of the material, then the grain structure in these areas is bound to change accordingly, it will be distorted or broken, and an extremely elongated boundary will be produced along the tearing direction. At this time, the grain boundary density of the stress area in the shear direction is bound to increase, which will lead to a corresponding increase in the iron loss inside the area. Therefore, the material in the stress zone can be considered as a high-loss material that falls on the ordinary lamination along the impact edge. In this way, the actual constants of the edge material can be determined, and the iron loss model can be used to further determine the actual loss of the impact edge.
As the main magnetic material of the motor, the performance compliance of silicon steel sheets has a great impact on the performance of the motor. The main thing is to ensure that the grade of silicon steel sheets meets the design requirements. In addition, the material performance of silicon steel sheets of the same grade from different manufacturers is somewhat different. When selecting materials, we should try our best to select materials from good silicon steel manufacturers. Here are some key factors that actually affect iron loss that we have encountered before.
⏩ The silicon steel sheets have not been insulated or have not been properly insulated. This type of problem can be found in the inspection process of silicon steel sheets, but not all motor manufacturers have this inspection project, and this problem is often not well identified by motor manufacturers.
⏩ The insulation between sheets is damaged or there is a short circuit between sheets. This type of problem occurs during the manufacturing process of the core. If the pressure during the lamination of the core is too large, the insulation between sheets will be damaged; or the burrs are too large after the punching of the sheet, and the burrs are removed by grinding, resulting in serious damage to the insulation on the surface of the sheet; and the slots are not smooth after the core is stacked, and the filing method is used; or the inner bore of the stator is not smooth, the inner bore of the stator is not concentric with the stop of the base, and other factors are corrected by turning. The conventional usage of these motor production and processing processes actually has a great impact on the performance of the motor, especially the iron loss.
⏩ When the winding is removed by burning or heating with electricity, the core will overheat, causing the magnetic conductivity to decrease and the insulation between the sheets to be damaged. This problem mainly occurs during the repair of the windings and the repair of the motor during the production and processing process.
⏩ Processes such as stacking welding will also cause the insulation between the stacks to be damaged and increase eddy current losses.
⏩ The iron weight is insufficient and the sheets are not compacted. The final result is that the core weight is insufficient, which will most directly lead to excessive current and excessive iron loss.
⏩ The silicon steel sheet is painted too thickly, causing the magnetic circuit to be too saturated. At this time, the relationship curve between the no-load current and voltage is more severely bent. This is also a key factor in the production and processing of silicon steel sheets.
⏩ The production and processing of the iron core will cause the destruction of the grain orientation of the silicon steel sheet punching and shearing surface, resulting in an increase in iron loss under the same magnetic induction; for variable frequency motors, there is also the additional iron loss caused by harmonics; this is a factor that should be comprehensively considered in the design process.