Apr. 10, 2020
The iron core is the basic component of the power transformer, which is composed of the iron core lamination, insulating parts, and iron core structural parts. The core body is composed of a magnetic steel strip with very high permeability. In order for different windings to induce a voltage proportional to the number of turns, the magnetic flux of the two windings is required to be equal, which requires a very high permeability in the winding For the core made of high material, try to make all the magnetic flux linked with two windings in the core, and make the magnetic flux linked with only one winding as little as possible.
In order to reduce the excitation current, the iron core is made into a closed magnetic circuit, and the iron core is the skeleton of the installed coil, which is an extremely important component for the electromagnetic performance, mechanical strength and transformer noise of the transformer.
The core laminations are formed by stacking or winding electrical magnetic steel belts. The core structural parts are mainly composed of clips, feet, braces, draw straps, pull screws and press nails. The structural parts ensure that the laminations are fully clamped to form a complete and firm core structure. There are insulating parts between the laminations and the clips, the feet, the supporting plates, the pull straps, and the pull plates. The core lamination leads the ground lead to the clamp or to the outside through the fuel tank to reliably ground, the core does not allow the existence of multi-point grounding. The lower clamp of the large transformer core is positioned by the positioning nails of the mailbox, and the positioning parts on the upper part of the core are coordinated with the fuel tank for positioning.
In order to reduce the no-load loss and no-load current of the transformer, besides the core is made of cold-rolled electrical magnetic steel strip with high permeability grain orientation, a series of measures are taken correspondingly in the structure, and the core is bound by oblique joints without holes In order to adapt to the directionality of cold-rolled oriented magnetic steel sheet and the use of symmetrical magnetic core structure.
The part of the core that is covered by the winding becomes the core post, and the other part that is not surrounded by the winding and forms the closed path of the magnetic flux becomes the iron yoke. The space defined by the core post and the iron yoke is the core window, and the size of the core window is related to the number and cross-sectional area of the winding.
Transformer cores are generally divided into two categories, namely shell cores, and core cores. Each type of iron core is divided into two types: stacked iron core and rolled iron core. Among them, the sheet-shaped electrical steel strips are stacked one by one to become a stacked core; the wound core is continuously wound with a ribbon-shaped material in a suitable shape mold on a winding machine. In addition, there is a double-frame iron core, that is, a large and small frame structure, but now because of the use of high-quality cold-rolled electrical magnetic steel strips, the width of the steel strip can already meet the requirements of the width of the core and the iron yoke, so the double frame (small and large frame) is rarely used. In addition, there are new double-frame and multi-frame structures, such as single-phase double-frame and three-phase four-frame structures.
If divided according to the number of phases of the transformer, the cores of single-phase transformers are collectively called single-phase cores, and the cores of three-phase power transformers are collectively called three-phase cores; they can also be classified according to the number of columns and frames of the transformer core.
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