Transformer core content sharing
The iron core is the main magnetic circuit part of the transformer. It is usually made of stacked hot-rolled or cold-rolled silicon steel sheets with high silicon content and coated with insulating paint. The iron core and the coil wound on it form a complete electromagnetic induction system. The transmission power of the power transformer depends on the material and cross-sectional area of the iron core.
1. High frequency type: Iron powder core Ferritecore
Ferritecore is used in high-frequency transformers. It is a ceramic magnet with a spinel crystal structure. This spinel is iron oxide and other divalent metal compounds. Such as kFe2O4 (k represents other metals), which are often used at present. The most common metals are manganese (Mn), zinc (Zn), nickel (Ni), magnesium (Ng), copper (Cu).
Its commonly used combinations are manganese-zinc (MnZn) series, nickel-zinc (NiZn) series and magnesium-zinc (MgZn) series. This material has high magnetic permeability and resistive properties, and its use frequency ranges from 1kHz to over 200kHz.
2. Low frequency category: silicon steel sheet (LAMINATION)
Silicon steel sheets are used in low-frequency transformers. There are many types. According to their different manufacturing processes, they can be divided into two types: A: calcined (black sheet), N: non-calcined (white sheet). According to their shapes, they can be divided into: EI type , UI type, C type, mouth type.
Mouth-shaped silicon steel sheets are often used in high-power transformers. They have good insulation performance, are easy to dissipate heat, and have short magnetic circuits. They are mainly used in high-power transformers with power greater than 500~1000W. A set of silicon steel sheets composed of two C-type silicon steel sheets is called CD-type silicon steel sheets. Under the condition of the same cross-sectional area, the power transformer made of CD-type silicon steel sheets has a higher window.
The larger the power of the transformer, the coils can be installed on both sides of the iron core, so the coil turns of the transformer can be distributed on the two wire packages, so that the average turn length of each wire package is shorter and the copper loss of the coil is reduced. In addition, if the two coils that require symmetry are respectively wound on the two wire packages, a completely symmetrical effect can be achieved. A set of silicon steel sheets composed of four C-type silicon steel sheets is called ED-type silicon steel sheets. The shape of the transformer made of ED-type silicon steel sheets is flat and wide. Under the same power condition, the ED-type transformer is shorter than the CD-type transformer, and the width Larger, and because the coil is installed in the middle of the silicon steel sheet and has an external magnetic circuit, the magnetic flux leakage is small and the overall interference is small. But all its coils are wound on a wire package, and the wire package is thicker, so the average turn length is longer , Copper consumption is larger.
The transformer produced by C-shaped iron core has small volume, light weight and high efficiency. From the perspective of assembly, C-shaped silicon steel sheet has few parts and strong versatility, so the production efficiency is high. However, the processing process of C-shaped silicon steel sheet is relatively complex. Many, the operation is more complicated, and it needs to be manufactured with special equipment, so the current cost is still relatively high.
E-type silicon steel sheets are also called shell-type or Japanese-type silicon steel sheets. Its main advantage is that the primary and secondary coils share a wire frame and have a high window space factor (space factor Km: net cross-sectional area of copper wire and window Area ratio); the silicon steel sheet forms a protective shell for the winding, making the winding less susceptible to mechanical damage; at the same time, the silicon steel sheet has a larger heat dissipation area, and the transformer magnetic field diverges less. However, its primary and secondary leakage inductance is large, and external magnetic field interference is also large , In addition, due to the longer average circumference of the winding, under the same number of turns and cross-sectional area of the core, the transformer with the EI core uses more copper wire.
The thickness of silicon steel sheets is commonly used in two types: 0.35mm and 0.5mm.
There are two ways of assembling silicon steel sheets: overlapping method and stacking method. The overlapping method is to distribute the openings of silicon steel sheets on both sides alternately one by one. This stacking method is more troublesome, but the gap between silicon steel sheets is small and the magnetic resistance is small. , which is conducive to increasing the magnetic flux, so power transformers all adopt this method. The overlapping method is often used in the occasions with DC current. In order to avoid saturation caused by DC current, a gap needs to be left between the silicon steel sheets, so the overlapping method will Put the E piece and I piece on one side, and the gap between the two can be adjusted with a piece of paper.
3. COIL class: divided into three types.
A. TOROID annular iron core: It is made of O-shaped laminated sheets, or rolled from silicon steel sheets. This kind of iron core is very difficult for winding.
B. RODCORE rod core.
C.DRUMCORE: drum core.