Why is the stator core made of laminated silicon steel sheets?

Commonly used transformer cores are generally made of silicon steel sheets. Silicon steel is a kind of steel that contains silicon (also called silicon), and its silicon content is between 0.8% and 4.8%. Silicon steel is used as the core of the transformer because silicon steel itself is a magnetic material with strong magnetic conductivity. In the energized coil, it can produce a large magnetic induction intensity, which can reduce the size of the transformer.

We know that the actual transformer always works under AC state, and the power loss is not only in the resistance of the coil, but also in the iron core under the magnetization of the alternating current. The power loss in the iron core is usually called "iron loss", and the iron loss is caused by two reasons, one is "hysteresis loss" and the other is "eddy current loss".

Hysteresis loss is the iron loss caused by the hysteresis phenomenon during the magnetization process of the iron core. The size of this loss is proportional to the area surrounded by the hysteresis loop of the material. The hysteresis loop of silicon steel is narrow, and the hysteresis loss of the iron core of the transformer is small, which can greatly reduce its heating degree.

Since silicon steel has the above advantages, why not use a whole piece of silicon steel as the core, but process it into sheets?

This is because the sheet core can reduce another kind of iron loss - "eddy current loss". When the transformer is working, there is an alternating current in the coil, and the magnetic flux it generates is of course alternating. This changing magnetic flux generates an induced current in the core. The induced current generated in the core circulates in a plane perpendicular to the direction of the magnetic flux, so it is called eddy current. Eddy current loss also causes the core to heat up. In order to reduce eddy current loss, the core of the transformer is stacked with silicon steel sheets that are insulated from each other, so that the eddy current passes through a smaller cross-section in a narrow loop to increase the resistance on the eddy current path; at the same time, the silicon in the silicon steel increases the resistivity of the material, which also plays a role in reducing eddy current.

For the core of the transformer, a 0.35mm thick cold-rolled silicon steel sheet is generally selected. It is cut into long sheets according to the required core size, and then overlapped into a "日" shape or a "口" shape. In theory, if you want to reduce eddy current, the thinner the silicon steel sheet is and the narrower the spliced strips are, the better the effect. This not only reduces eddy current loss and temperature rise, but also saves silicon steel sheet materials. But in fact, when making silicon steel sheet cores, it is not just based on the above-mentioned favorable factors, because making the core in that way will greatly increase the working hours and reduce the effective cross-section of the core. Therefore, when using silicon steel sheets to make transformer cores, it is necessary to weigh the pros and cons based on the specific situation and choose the best size.

The transformer is made according to the principle of electromagnetic induction. There are two windings on the closed iron core column, a primary winding and a secondary winding. When the primary winding is energized by an AC power supply voltage, an alternating current flows through the primary winding and a magnetic potential is established. Under the action of the magnetic potential, an alternating main magnetic flux is generated in the iron core. The main magnetic flux passes through the iron core at the same time, {interlinking] the secondary winding and is closed. Due to the electromagnetic induction effect, the secondary winding generates an induced electromotive force. As for why it can boost and reduce voltage, it needs to be explained by Lenz's law. The magnetic flux generated by the induced current always hinders the change of the circular magnetic flux. When the primary magnetic flux increases, the magnetic flux generated by the induced current is opposite to the primary magnetic flux. That is to say, the induced magnetic flux generated by the secondary winding is opposite to the main magnetic flux generated by the primary winding, so a low-level alternating voltage appears in the secondary winding,,,

So...The iron core is the magnetic circuit part of the transformer. Silicon steel sheet is commonly known as silicon steel sheet or silicon steel sheet. As the name implies, it is electrical silicon steel with a silicon content of 0.8%-4.8%, which is made by hot and cold rolling. The thickness is generally less than 1mm, so it is called a thin plate. Silicon steel sheets generally belong to the category of plates, but due to its special use, it has become an independent branch. Electrical silicon steel sheets have excellent electromagnetic properties and are an indispensable and important magnetic material in the power, telecommunications and instrumentation industries. (1) Classification of silicon steel sheets A. Silicon steel sheets can be divided into low silicon and high silicon according to their silicon content. Low silicon sheets contain less than 2.8% silicon, and have a certain mechanical strength. They are mainly used to manufacture motors, commonly known as motor silicon steel sheets; high silicon sheets contain 2.8%-4.8% silicon, and have good magnetic properties, but are relatively brittle. They are mainly used to manufacture transformer cores, commonly known as transformer silicon steel sheets. There is no strict boundary between the two in actual use, and high silicon sheets are often used to manufacture large motors. B. According to the production and processing technology, they can be divided into hot rolling and cold rolling. Cold rolling can be divided into two types: grain-free and grain-oriented. Cold-rolled sheets have uniform thickness, good surface quality and high magnetic properties. Therefore, with the development of industry, hot-rolled sheets tend to be replaced by cold-rolled sheets (my country has clearly required the cessation of the use of hot-rolled silicon steel sheets, which is what we called "cold instead of hot" in the early stage).

(2) Performance indicators of silicon steel sheets

A. Low iron loss. The most important indicator of quality. All countries in the world classify grades according to iron loss values. The lower the iron loss, the higher the grade and the higher the quality.

B. High magnetic induction intensity. Silicon steel sheets that can obtain higher magnetic induction under the same magnetic field have smaller volume and weight for motor or transformer cores made of them, which can save silicon steel sheets, copper wires and insulation materials. C. High stacking coefficient. The surface of silicon steel sheets is smooth, flat and uniform in thickness, which improves the stacking coefficient of the core.

D. Good punching performance. This is more important for the manufacture of small and micro motor cores.

E. Good adhesion and weldability to the insulating film on the surface.

F. Magnetic aging

G. Silicon steel sheets must be delivered after annealing and pickling.

(I) Hot-rolled silicon steel sheet for electrical use (GB5212-85)

Hot-rolled silicon steel sheet for electrical use is made of ferrosilicon soft magnetic alloy with low carbon loss, and is hot-rolled into a sheet with a thickness of less than 1mm. Hot-rolled silicon steel sheet for electrical use is also called hot-rolled silicon steel sheet.

Hot-rolled silicon steel sheets can be divided into two types of steel sheets: low silicon (Si≤2.8%) and high silicon (Si≤4.8%) according to their silicon content.

(II) Cold-rolled silicon steel sheet for electrical use (GB2521-88)

It is made of electrical silicon steel with a silicon content of 0.8%-4.8%, and is cold-rolled.

Cold-rolled silicon steel sheets are divided into two types of steel strips: grain-free and grain-oriented. Cold-rolled electrical steel strips have the characteristics of smooth surface, uniform thickness, high stacking coefficient, good punching performance, etc., and have higher magnetic induction and lower iron loss than hot-rolled electrical steel strips. Using cold strip instead of hot rolled strip to manufacture motors or transformers can reduce their weight and volume by 0%-25%. If cold rolled oriented strip is used, the performance is better. Using it instead of hot rolled strip or low-grade cold rolled strip can reduce the transformer's power consumption by 45%-50%, and the transformer's working performance is more reliable.

Used to manufacture motors and transformers. Usually, grain non-oriented cold rolled strip is used as the state of motors or welding transformers, etc.; grain oriented cold rolled strip is used as the core of Power Transformers, pulse transformers and magnetic amplifiers, etc.

Steel plate specifications: thickness of 0.35, 0.50, 0.65mm, width of 800-1000mm, length of ≤2.0m.

(III) Hot rolled silicon steel sheet for household appliances (GBH46002-90)

The brand of hot rolled silicon steel sheet for household appliances is represented by J (home) D (electricity) R (hot rolled), that is, JDR. The number after JDR is the iron loss value*100, and the number after the horizontal line is the steel plate thickness (mm)*100. The electromagnetic performance requirements for hot-rolled silicon steel sheets for household appliances can be slightly lower, and the minimum iron loss value (P15/50) is 5.40W/kg. Generally, it is delivered without washing.

Used for differential motors of various household appliances such as electric fans, washing machines, vacuum cleaners, and range hoods.