Once a power supply transformer is designed, most engineers will try to wind it to make sure particular design is reasonable, because most of transformer is still a structural problem and some issues need to be addressed. to when winding transformer First, this is definition of our skeleton. Which core skeleton is used is very different for transformer winding. For example, for same AP, cross-sectional area Ae of magnetic core is small, but winding space Aw is relatively large. You can choose one with a large Ae value and relatively small winding space.
Once you have determined magnetic core and skeleton, you can calculate number of turns of primary side and secondary side, and then calculate cross-sectional area of the winding wire to be used according to effective value of passed current. through coil. The winding wire diameter calculated here is only cross-sectional area of pure copper wire, our transformer winding wires include enamelled wire, stranded wire, triple insulated wire, coated wire, copper foil, etc. Need to pay attention attention to selection of wires when winding transformers:
1: Enamelled wire is a copper wire covered with a thin layer of paint, called an electrical insulating layer, which contains oil, resin, pigment, filler and solvent. In order to meet requirements of electrical insulation, film structure of electrical insulating paint is different from that of ordinary paint film, it has large resistivity, good thermal conductivity, good mechanical properties and good moisture resistance, and has a certain pressure and temperature. resistance. when I wind transformer, number of turns is close to each other.
2. Stranded wire consists of several enameled wires. As a rule, one wire has a diameter of 0.1 mm, and then several strands. For example, 50 strands of wire with a diameter of 0.1 mm are twisted together. Such wires are generally used to reduce skin effect. When diameter of a single wire exceeds 0.5mm, it is not recommended to use a single wire. As a rule, stranded wires are used. There is no difference between stranded wires. and enamelled wires.
3. Silk coated wire refers to an electromagnetic wire made of a layer of natural silk or silk fiber (nylon, polyester fiber, natural silk, self-adhesive silk, etc.) wound on outside of wire or enameled stranded wire as an insulating layer. Coated wire silk, has better insulation than stranded wire.
4. Triple Insulated Wire Triple insulated wire is a high performance insulated wire that has three layers of insulatingmaterial, middle layer is core, outer layer is transparent glass fiber, middle layer is a colored coating. innermost layer is a polyamide film only a few microns thick, called "gold film" in foreign markets, but it can withstand 3KV impulse high voltage. The total thickness of insulating material does not exceed 100 µm. Therefore, when we calculate a transformer, if we want to use triple insulated wire, we usually add 0.2 mm to outside diameter.
5. Copper foil is usually used when outputting large current. As a general rule, when choosing copper foil, you must select width and thickness of copper foil. The width of copper foil is selected according to skeleton of core, and then calculated according to required thickness of the cross-sectional area.
When I know material of wire, when I select wire, I will select appropriate wire diameter according to needs. According to requirements of safety regulations, whether to choose a retaining wall or choose a single-sided winding with three-layer insulation, cost of using three-layer insulated wire is High, but less man-hours around retaining wall, which shortens winding process, if source and secondary sides use enameled wire, a retaining wall must be added.
When adding a retaining wall, keep in mind that thickness of retaining wall must be same as thickness of winding. After winding winding, if necessary, add an interlayer insulating tape, and then add next winding. Generally, creepage distance between primary winding and secondary winding should be 6mm, that is, primary winding should have a retaining wall with a thickness of 3mm, and secondary winding should also add a retaining wall. wall thickness of 3 mm.
In process of winding, it is necessary to pay attention to winding. As a rule, it is tightly wound. If one layer cannot be wound, it must be evenly distributed. This facilitates winding of next winding. During winding process, there should be no overlap of turns and windings. Wind wire around retaining wall.
That's why you need to avoid winding deformation and not waste space for winding. If it goes around retaining wall, then safety regulations on original side are not enough.
Because tape is not necessarily flat during winding process, width of tape should be 0.5 mm larger than width of bony groove of framework. usually Teflon case, size should be enough to cover winding wire, which can reduce winding space, and you need to pay attention to location of case. Figure 2. During the winding process, two phenomena B and C in fig. 2 should not appear.
After AC winding is wound, magnetic core is assembled. Before assembling magnetic circuit, it is necessary to open an air gap to control inductance. Open air gap usually has two types of folded air gaps and grinding air gaps. General engineers The samples made by me are all air gaps, because there is no professional equipment. If it is a product, it is better to grind air gap as much as possible. From experience, EMI grinding air gap will be better, and air gap is almost same, but air gap efficiency of gap will be higher. wall tape. When air gap is adjusted, it is assembled. When assembling, magnetic core must be joined, and then, after pressing, fixed with adhesive tape. Fixation is also with yellow tape. In general, 2-3 layers are required, and then electrical parameters and safety regulations are measured. After testing, entire transformer is manufactured .
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