Magnetic Cores For Transformers And Transformers

Q1: The magnetic material used in transformers, transformers and inductors is called magnetic core or iron core. Are there specs?

Nowadays, many people call the ring made of silicon steel as iron core, because the main component of silicon steel is iron, so the ring made of silicon steel is called iron core. The rest of the magnetic material, such as ferrite, is called the core. This name is actually very unscientific, it is not a name from the appearance, silicon steel is indeed made of iron as the main component, but you should know that basically all core materials contain iron materials, from this point of view See, all core materials can be called iron cores.

However, the magnetic properties of soft magnetic materials used in transformers vary with electric fields, and b-h magnetic fields are generated. The magnetic field changes from an electric field to a magnetic field, and then from a magnetic field to an electric field. Because of how magnetic field conversion works, it is not necessary to refer to the magnetic material as a magnetic core in this regard.

Above I just want to explain that according to the current development of magnetic materials, there is no need to artificially distinguish the difference between magnetic core and iron core. In the future, if the transformer still relies on electromagnetic conversion and the magnetic material does not contain iron, it will be called a magnetic core. If it does not rely on electromagnetic conversion, but still contains ferrous material, it is called an iron core. But so far, there is no uniform standard.

Question 2: How are magnetic materials classified?

According to the magnetic properties, magnetic materials can be divided into hard magnetic materials (permanent magnetism) and soft magnetic materials. Hard magnetic materials are those that remain magnetic after the magnetic field is removed. Hard magnetic materials are commonly used in the manufacture of various permanent magnets, electromagnetic steel for speakers, and storage elements in electronic circuits. A soft magnetic material is a material that has a high magnetic induction in the presence of a magnetic field, but loses its magnetic properties when the magnetizing field is removed. Due to this characteristic, soft magnetic materials are used in the manufacture of magnetic core components for transformers, transformers, inductors and other products that require electromagnetic conversion.

Figure 1: The hysteresis loop of the soft magnetic material is slender and the coercive force HC and the residual magnetic flux Br are small, while the hysteresis loop of the hard magnetic material is large, the coercive force HC and the residual magnetic flux Br are large.

Question 3: What is a soft magnetic material? What are its characteristics?

Soft magnetic materials usually have three ferromagnetic elements, iron, cobalt and nickel, which are the basic components of magnetic materials. Soft magnetic materials are generally classified as:

1. Powder core: iron powder core, iron, silicon and aluminum powder core, high magnetic flux powder core and permalloy powder core (MPP). Dusted iron cores are characterized by good frequency characteristics and low losses at high frequencies, and are often used in high frequency inductors.

2. Types of ferrite cores: mainly divided into nickel-zinc and manganese-zinc. For high frequency inductors, manganese and zinc are used as low frequency filter inductors. Transformers for switching power supplies usually use ferrite as the core, but use different ferrite materials depending on the frequency.

3. Silicon steel sheet iron core: Silicon steel sheet is an alloy. The iron-silicon alloy formed by adding a small amount of silicon (usually less than 4.5%) to pure iron is called silicon steel. The saturation magnetic induction of this core is 2T. They have the advantages of good magnetoelectric properties, easy mass production, low cost, and little influence of mechanical stress, so they are widely used in the power electronics industry, especially in the field of low frequency and high power. Such as transformers, transformers, inductance and reactance.

4. Permalloy: Permalloy usually refers to an iron-nickel alloy with a nickel content in the range of 30~90%. It is a widely used soft magnetic alloy. The magnetic properties can be controlled by appropriate processes. The saturation magnetic induction intensity is slightly lower than that of silicon steel, but the magnetic permeability is dozens of times higher than that of silicon steel, and the iron loss is 2-3 times lower than that of silicon steel. Due to its high initial permeability, it is usually suitable for zero-sequence current mutual inductance

5. Nanocrystal: Nanocrystal k107(1) is developed on the basis of amorphous state (1 k101), with high magnetic permeability and high magnetic induction intensity (1.2 T), it can be said that the comprehensive ability of magnetic nanocrystal is good. The magnetic materials can also be applied to various electromagnetic conversion products, including transformers, transformers, inductors, and reactances are the right choice. The disadvantage is that the physical properties are poor, resulting in fewer varieties.

Q4. What are the characteristics of the magnetic core used in the transformer? That is, how to choose the magnetic core of the transformer?

To know how to choose a transformer core, it will be someone who understands the performance parameters of the transformer. The performance of the transformer is mainly based on high precision and strong load capacity. Therefore, to achieve high precision, the core material of the transformer will choose a relatively high magnetic permeability. High magnetic materials, such as amd crystals (also known as nanocrystals), to have higher load capacity, and choose magnetic materials with higher magnetic induction, such as silicon steel (also known as an). Of course, transformers usually use one type of magnetic core, so core selection is a comprehensive process.

Below is a list of common magnetic materials used in transformers (see Table 1).

Therefore, the comprehensive condition should be that nanocrystals are the materials for making transformers. They allow transformers with a high level of precision and a certain load. However, considering the price, the price of nanocrystalline is much higher than that of silicon steel, and it is difficult to process transformers from silicon steel. So conventional primary transformers (output 5/1A) now use silicon steel cores. A high level of precision is required, using nanocrystals. For secondary transformers (outputting milliamps of current), nanocrystals are often used due to their precision grade requirements. For transformers with accurate ratings and low load requirements, mn-zn ferrite cores can also be used considering cost.

Therefore, the core of the transformer should be selected according to the actual situation.

Question 5: What are the characteristics of the magnetic core used in the transformer? That is, how to choose the magnetic core of the transformer?

Transformers are generally divided into power frequency transformers, intermediate frequency transformers and high frequency transformers, so the magnetic core is mainly selected according to the frequency. If the wrong core is used, the loss of the transformer will increase in the light case, and in the heavy case, the transformer will burn out from saturation of the magnetic core.

Generally, silicon steel sheets are suitable for transformers below 400HZ. (Of course, the thinner the silicon steel is now, the higher the frequency it can be used, but the cost is high). Nanocrystals are materials for medium and high frequency transformers due to their good frequency characteristics and high magnetic induction. However, various types of lower cost ferrites are commonly used in high frequency transformers due to the high cost and difficulty of designing many forms of the material.

(Please indicate the source of the reprint, Jiangyin Xinghuo Electronic Technology Co., Ltd.)