Analysis of Iron Core in Transformer
Release time:
2023-11-17
The core is the basic absence of power transformers, consisting of core laminations, insulating parts and core structural parts. The core body is composed of magnetic steel strips with high magnetic permeability. In order to enable different windings to induce voltages proportional to the number of turns, the magnetic fluxes of the two windings are required to be equal. This requires a core made of materials with high magnetic permeability in the windings, so that all magnetic fluxes are linked in the core and the two windings as much as possible, and the magnetic fluxes linked with only one winding are as few 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 coil, which is extremely important for the electromagnetic performance, mechanical strength and transformer noise of the transformer.
The core laminations are formed by stacking or winding electrical magnetic steel strips, and the core structural parts are mainly composed of clamps, pads, bracing plates, pulling belts, pulling screws and pressing nails. The structural members ensure sufficient clamping of the laminations to form a complete and strong core structure. Laminations and clamps, footings, braces, straps and plates are insulated. The grounding lead of the iron core lamination is connected to the clamp or to the external reliable grounding through the mailbox, and the iron core is not allowed to have multi-point grounding. The lower clamping part of the large transformer core is positioned by the positioning nail of the mailbox, and the positioning part on the support plate on the upper part of the core is matched with the mailbox.
In order to reduce the no-load loss and no-load current of the transformer, the iron core is made of high-permeability grain-oriented cold-rolled electrical magnetic steel strip, and a series of corresponding measures are taken in the structure, such as oblique joint non-porous binding iron core, so as to adapt to the directionality of cold-rolled oriented magnetic steel sheet and the core structure with symmetrical magnetic circuit.
The part of the core covered by the winding becomes the core column, and the other part that is not surrounded by the winding to form the closed path of the magnetic flux becomes the iron yoke. The space determined by the core column 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 windings.
Transformer iron core is generally divided into two categories, namely shell type iron core and core type iron core. Each type of iron core is divided into two types: stacked iron core and rolled iron core. Among them, the sheet-like electrical steel strip is stacked one by one to become a laminated core; the coil core is continuously wound with a strip material on a winding machine with an appropriate shape mold. In addition, there are double-frame iron cores, I .e. large and small frame structures. However, due to the high-quality cold-rolled electrical magnetic steel strips, the width of the steel strips can meet the requirements of the width of the core column and iron yoke, so double-frame (large and small frame) iron cores are 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 according to the number of transformer phase points, the core of single-phase transformer is collectively referred to as single-phase core, three-phase transformer core is collectively referred to as three-phase core; can also be classified according to the number of transformer core columns, frame number, etc.