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Magnetic core for mutual inductor and transformer

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Magnetic core for mutual inductor and transformer

2017/04/07 00:00
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Q1: the magnetic materials used in mutual inductors, transformers and inductors are called magnetic cores or iron cores. Are there any specifications?
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. And the rest of the magnetic materials, such as ferrite, nanocrystalline are called magnetic core. This name is actually very unscientific, not from the appearance to give it a name, silicon steel is indeed made of iron as the main component, but you should know that basically all core materials contain iron material, all from this point of view, all core materials can be called iron core.
However, the magnetic property of the soft magnetic material used in the transformer is changed with the electric field, and the b-h magnetic field is generated. The magnetic field is changed from the electric field to the magnetic field, and then from the magnetic field to the electric field. Because of the working principle of magnetic field conversion, it is not necessary to call the magnetic material a magnetic core in this respect.
Above I just want to explain that on the basis of the current development of magnetic materials, it is not necessary to distinguish the difference between magnetic core and iron core artificially. In the future, if the transformer still relies on electromagnetic conversion and the magnetic material does not contain iron, it is called magnetic core. If there is no need to rely on electromagnetic conversion, but still contains iron material, it is called iron core. But up to now, there is no standard for its unity.
Q2: how are magnetic materials classified?
According to the magnetic properties, magnetic materials can be divided into hard magnetic materials (permanent magnetic) and soft magnetic materials. Hard magnetic materials are materials that can still be magnetic after the magnetic field is removed. Hard magnetic materials are commonly used to make various permanent magnets, magnetic steel of speakers and memory elements in electronic circuits. Soft magnetic material is a kind of material that has high magnetic induction intensity when the magnetic field exists, and loses its magnetism when the magnetization field is removed. Due to this characteristic, soft magnetic material is used to make magnetic core components for mutual inductors, transformers, inductors and other products requiring electromagnetic conversion. (see figure 1)
Figure 1: hysteresis loop of soft magnetic material is slender, coercivity HC and residual flux Br are small, hysteresis loop of hard magnetic material is large, coercivity HC and residual flux Br are large.
Question 3: what are soft magnetic materials and what are their characteristics?
Soft magnetic materials usually have iron, cobalt, nickel three ferromagnetic elements 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 Flux powder core and permalloy powder core (MPP). Powder core magnetic core is characterized by good frequency characteristics and low loss at High frequency, commonly used in high-frequency inductance.
2, ferrite core category: mainly divided into nickel and zinc and manganese zinc, nickel and zinc permeability is low, but good frequency characteristics, manganese and zinc permeability permeability is relatively good, but the frequency characteristics is relatively poor, nickel and zinc is usually used in high frequency inductance, manganese and zinc used as low frequency filter inductance. Transformers for switching power supply usually use ferrite as the core, but different ferrite materials are used according to the frequency.
3, silicon steel sheet iron core: silicon steel sheet is an alloy, in the addition of a small amount of silicon in the pure iron (generally less than 4.5%) the formation of iron silicon alloy known as silicon steel. The maximum saturation magnetic induction intensity of this kind of core is 2T. They are widely used in power electronics industry, especially in low frequency and high power, because of their advantages such as good magnetoelectric performance, easy mass production, low price and little influence of mechanical stress. Such as transformers, mutual inductors, inductance and reactance.
4, permalloy: permalloy usually refers to the fe-ni alloy, nickel content in the range of 30~90%. It is a widely used soft magnetic alloy. The magnetic properties can be effectively controlled by proper process. 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, nanocrystalline: nanocrystalline k107 (1) is on the basis of amorphous (1 k101) developed, has high permeability, high magnetic induction intensity (1.2 T), can say is magnetic nanocrystals comprehensive ability best magnetic material, also can apply to various products of electromagnetic transformation, including transformer, transformer, inductance, reactance is right choice. Its disadvantage is poor physical properties, 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 select the transformer core, that'll be the first to understand the performance parameters of transformer, the performance of the transformer is the most main is precise level is high, the load capacity is strong, so to achieve high accuracy level, on the transformer core material will choose relatively high permeability of magnetic materials, such as amd crystal (also known as nanocrystalline) to load ability choose high magnetic induction intensity of magnetic materials, such as silicon steel (also called an). Of course, one kind of magnetic core is normally used in the transformer, so the selection of magnetic core is a process of comprehensive consideration.
The following is a list of common magnetic materials used in the transformer (see table 1).
Therefore, the comprehensive conditions should be that nanocrystals are the best materials for making transformers. They can make transformers with the highest accuracy level 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 the transformer with silicon steel. Therefore, the conventional primary transformer (output 5A/1A) now USES silicon steel core. High accuracy level is required, nanocrystalline is used. For the secondary transformer (output mA level current), due to its high accuracy level requirements, generally using nanocrystalline. For the transformer with accurate grade and low load requirement, the magnetic core of mn-zn ferrite can also be used considering the cost.
Therefore, how to choose the magnetic core of the transformer should be based on the actual situation.
Question 5: what are the characteristics of the magnetic cores used in transformers? Is how to choose the magnetic core of transformer namely?
Transformers are generally divided into power frequency, intermediate frequency and high frequency transformers, so the magnetic core is mainly selected according to the frequency. If the wrong magnetic core is used, the loss of the transformer will increase in the light case, and the transformer will burn down due to the saturation of the magnetic core in the heavy case.
Generally, silicon steel sheet is suitable for transformers below 400HZ. (of course, the thinner the silicon steel is now, the higher frequency can be used, but the cost is very high). Nanocrystals are excellent materials for medium-high frequency transformers because of their good frequency characteristics and high magnetic induction strength. However, due to the high cost and the difficulty in designing multiple forms of materials, the ferrite with various types and low cost are commonly used in high-frequency transformers.
(please indicate the source of reprint, jiangyin xinghuo electronic technology co., LTD.)