The transformer core is divided into three types: high frequency, low frequency and COIL:
1, high frequency: iron powder core ferrite core
Ferrite cores are used in high frequency transformers. It is a ceramic magnet with a spinel crystal structure. Spinels are iron oxide and other divalent metal compounds. For example, kFe2O4 (k stands for other metals), commonly used metals are manganese (Mn), zinc (Zn), nickel (Ni), magnesium (Ng), copper (Cu).
Commonly used combinations are the manganese zinc (MnZn) series, the nickel zinc (NiZn) series and the magnesium zinc (MgZn) series. The material has high magnetic permeability and resistive physical properties and is used in frequencies ranging from 1 kHz to over 200 kHz.
2, low frequency class: silicon steel sheet (LAMINATION)
Silicon steel sheets are used for low frequency transformers. There are many types of silicon steel sheets, which can be divided into different manufacturing processes.
A: Calcination (black film)
N: no calcination (white film).
According to its shape, it can be divided into: EI type, UI type, C type and mouth type.
Oral silicon steel sheets are commonly used in transformers with high power. They have good insulation properties, easy to dissipate heat and magnetic short circuits. They are mainly used for power transformers with powers greater than 500~1000W and high power.
A group of silicon steel sheets composed of two C-type silicon steel sheets is referred to as a CD type silicon steel sheet. Power transformers made of CD-type silicon steel sheets have the same cross-sectional area, and the higher the window, the greater the power of the transformer. The coils can be mounted separately on both sides of the core so that the number of turns of the transformer can be distributed over the two harnesses, so that the average length of each coil is shortened and the copper loss of the coil is reduced. Reduced. In addition, if two coils that are symmetrical are required to be wound on two wire packages, a completely symmetrical effect can be achieved.
A group of silicon steel sheets composed of four C-type silicon steel sheets is called an ED type silicon steel sheet. A transformer made of ED silicon steel sheet has a flat and wide shape. At the same power, the ED transformer is shorter and wider than the CD type transformer. In addition, since the coil is mounted in the middle of the silicon steel sheet, there is an external magnetic circuit, so the leakage magnetism is small and the overall interference is small. However, all of its coils are wound around the wire package, and the wire package is thicker, so the average length is longer and the copper consumption is greater.
The C-type iron core has excellent performance, small volume, light weight and high efficiency. From the point of view of assembly, the C-type silicon steel sheet has few parts, strong versatility and high production efficiency, but the C-type silicon steel sheet has a better processing technology. Many of the more complex needs to be manufactured using special equipment, so the current cost is still high.
We mainly use EI type silicon steel plate. E-type silicon steel sheets are also called shell-type or Japanese-type silicon steel sheets. The main advantage is that the primary and secondary coils have a common wireframe and have a high window duty factor (duty factor Km: net cross-sectional area of the copper wire and window). Area ratio); the silicon steel sheet forms a protective outer casing for the winding, so that the winding is not easily damaged by mechanical damage; at the same time, the heat dissipation area of the silicon steel sheet is large, and the magnetic field dispersion of the transformer is small. However, its primary and secondary leakage inductances are large and the external magnetic field interference is also large. In addition, since the average circumference of the winding is long, the copper wire used in the transformer of the EI core is compared under the same number of turns and the cross-sectional area of the core. a lot of.