The iron core is the main magnetic circuit part of a transformer. It is usually made of hot-rolled or cold-rolled silicon steel sheets with high silicon content and coated with insulating varnish. The iron core and the coils wound on it form a complete electromagnetic induction system. The power transmitted by a transformer depends on the material and cross-sectional area of the iron core.

Classification Introduction

1. High frequency: Ferrite core

Ferrite core is used in high-frequency transformers. It is a ceramic magnet with a spinel crystal structure. This spinel is a compound of iron oxide and other divalent metals. For example, kFe2O4 (k stands for other metals), which often used at present are manganese (Mn), zinc (Zn), nickel (Ni), magnesium (Ng), and copper (Cu).

Its commonly used combinations are manganese-zinc (MnZn) series, nickel-zinc (NiZn) series and magnesium-zinc (MgZn) series. This material has high permeability and resistive properties, and its use frequency ranges from 1kHz to more than 200kHz.

2. Low frequency category: silicon steel sheet (Lamination)

Silicon steel are used in low-frequency transformers, and there are many types. According to their different production processes, they can be divided into A: annealed(black sheet) and N: non-annealed (white sheet). According to their different shapes, they can be divided into: EI core , UI core, C core, mouth core.

Mouth-shaped silicon steel cores are often used in transformers with higher power. They have good insulation properties, are easy to dissipate heat, and have a short magnetic circuit. They are mainly used in high-power transformers with power greater than 500~1000W. A set of silicon steel cores composed of two C-type cores is called CD core. The power transformer made of CD cores has the same cross-sectional area, and the bigger window size the biiger power of the transformer. 

The coils can be installed on both sides of the iron core, so the number of turns of the transformer can be allocated to the two coils, so that the average turn length of each coil is shorter and the copper loss of the coil is reduced. In addition, if two coils that require symmetry are wound on two coils respectively, 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 transformer is shorter than the CD transformer. Larger, in addition, because the coil is installed in the middle of the silicon steel sheet, there is an external magnetic circuit, so the magnetic leakage is small, and the overall interference is small. However, all the coils are wound on a wire package, which is thicker, so the average turn length is longer , The copper consumption is relatively large.

The transformer produced by the excellent performance of the C-type iron core is small in size, light in weight and high in efficiency. From the perspective of assembly, the C-type silicon steel sheet has few parts and is highly versatile, so the production efficiency is high. However, the C-type silicon steel sheet has a relatively high processing process. It is more complicated and requires special equipment to manufacture, so the current cost is still relatively high.

E-type silicon steel sheet is also called shell-type or Japanese-type silicon steel sheet. Its main advantage is that the primary and secondary coils share the same wire frame and have a higher window space factor (occupancy factor Km: net cross-sectional area of copper wire and window Area ratio); the silicon steel sheet forms a protective shell on the windings, so that the windings are not easily damaged by mechanical damage; at the same time, the silicon steel sheet has a larger heat dissipation area and less magnetic field divergence of the transformer. But its primary and secondary leakage inductance is larger, and the external magnetic field interference is also larger In addition, due to the long average circumference of the winding, under the same number of turns and core cross-sectional area, the transformer with the EI core uses more copper wires.