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1. High frequency: Ferrite core

Ferrite core is used in high-frequency transformers. It is a ceramic magnet with a crystalline structure of spinel, which is iron oxide and other bivalent metallic compounds. Such as kFe2O4(k represents other metals), currently commonly used metals are manganese (Mn), zinc (Zn), nickel (Ni), magnesium (Ng), copper (Cu). Its common combinations such as manganese zinc (Mn Zn) series, nickel zinc (Ni Zn) series and magnesium zinc (Mg Zn) series. This material has high permeability and impedance physical properties, its use frequency range from 1kHz to more than 200kHz.

2. Low frequency: LAMINATION

Silicon steel sheet is used for low frequency transformer, there are many kinds, according to its different production process can be divided into A: forging (black), N: no forging (white) two kinds. According to its shape can be divided into: EI type, UI type, C type, mouth type.

Mouth type silicon steel sheet is often used in transformers with large power. It has good insulation performance, easy heat dissipation and short magnetic circuit. It is mainly used in transformers with power greater than 500~1000W and high power. A set of silicon steel sheets composed of two C-type silicon steel sheets is called CD type silicon steel sheet. The power transformer made of CD type silicon steel sheets has the same cross-sectional area. The higher the window is, the greater the transformer power will be. The coil can be installed separately on both sides of the core, so the number of turns of the transformer coil can be distributed on the two wire packets, so that the average turn length of each wire packet is shorter, and the copper consumption of the coil is reduced. In addition, if the two coils required to be symmetrical are wound separately on the two wire packages, the effect of complete symmetry can be achieved.

A set of four C-type silicon steel sheets is called ED type silicon steel sheets. The transformer made of ED type silicon steel sheet has a flat and wide shape. Under the condition of the same power, ED type transformer is shorter and wider than CD type transformer. 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 interference to the whole is small. However, all the coils are wound on a wire package, which is thicker, so the average turn length is longer and the copper consumption is larger.

The transformer made of C-type iron core with excellent performance is small in volume, light in weight and high in efficiency. From the point of view of assembly, C-type silicon steel sheet has few parts and strong in universality, so the production efficiency is high. However, C-type silicon steel sheet has many processing procedures, which is more complex and requires special equipment to manufacture, so the cost is still high at present.

E type silicon steel sheet is also known as shell type or solar type silicon steel sheet. Its main advantages are that the primary and secondary coils share a wire frame and have a higher window duty coefficient (duty coefficient Km: copper wire net cross-sectional area and window area ratio); The silicon steel sheet forms a protective shell on the winding, so that the winding is not easy to be damaged by mechanical damage; At the same time, the heat dissipation area of the silicon steel sheet is larger and the magnetic field of the transformer is less divergent. However, its leakage induction of primary stage is larger, and the interference of external magnetic field is also larger. In addition, due to the longer average perimeter of winding, the transformer of EI type iron core uses more copper wires under the condition of the same number of turns and core cross-sectional area.

The thickness of silicon steel sheet is commonly used in 0.35mm and 0.5mm.

There are two ways of assembling silicon steel sheet: overlapping method and overlapping method. The overlapping method is to distribute the openings of the silicon steel sheet one to one alternately on both sides. This overlapping method is more troublesome, but the gap of the silicon steel sheet is small, and the reluctance is small, which is conducive to increasing the flux. Therefore, the power transformer adopts this method. The stacking method is often used in the situations where DC current passes through. In order to avoid saturation caused by DC current, there needs to be a gap between the silicon steel sheet. Therefore, the stacking method puts the E sheet and the I sheet aside, and the gap between the two can be adjusted by paper.

3.COIL: There are three types.

A.oid ring core: made of O-type laminated, or wound by silicon steel sheet. This kind of iron core is very difficult to wind.

B. OD CORE Rod shaped iron core.

C.DRUM CORE C. d rum core

The role of transformer core

The actual transformer core works in AC state, and the power loss is not only in the resistance of the coil, but also in the core under alternating current magnetization. The power loss in the iron core is usually called "iron loss". The iron loss is caused by two reasons, one is "hysteresis loss" and the other is "eddy current loss". Hysteresis loss is the iron loss caused by the existence of hysteresis phenomenon in the process of magnetization of the iron core. The size of this loss is proportional to the size of the area surrounded by the hysteresis loop of the material. The hysteresis loop of silicon steel is narrow, and the hysteresis loss of transformer core is small, which can greatly reduce its heating degree. Since silicon steel has the above advantages, why not use a whole piece of silicon steel as the core, but also process it into sheets? This is because the sheet core reduces another type of iron loss, called eddy current loss. When a transformer works, there is alternating current in the coil, and the flux it produces is of course alternating. This changing flux creates an induced current in the core. The induced current generated in the core circulates in a plane perpendicular to the direction of the magnetic flux, so it is called a vortex. Eddy current loss also heats the core. In order to reduce the eddy current loss, the transformer core is stacked with silicon steel sheets insulated from each other, so that the eddy current passes through a small section in the narrow and long circuit to increase the resistance on the eddy current path. At the same time, the silicon in the silicon steel increases the resistivity of the material, but also plays a role in reducing the equal eddy current.