Nov. 17, 2020
A power transformer is one of the most important equipment in the power system, and it is the basis to ensure the reliability of the power supply. With the rapid development of the entire national economy, the demand for transformers will continue to increase.
However, as the installed capacity of power transformers increases, the energy consumed by them is also increasing, which is inconsistent with my country's advocacy of building an energy-saving society.
It is necessary to take corresponding technical measures to reduce the loss of the transformer itself, so it becomes very necessary to study how to reduce the iron loss of the transformer.
The loss of power transformer mainly includes two parts: no-load loss and load loss.
The no-load loss of the transformer mainly includes the hysteresis loss, eddy current loss, and additional loss of the core material, and because the no-load loss of the transformer belongs to the excitation loss, it has nothing to do with the load.
1) Hysteresis loss is the loss caused by the hysteresis phenomenon in the process of repeated magnetization of ferromagnetic materials. The size of the hysteresis loss is proportional to the area of the hysteresis loop.
2) Eddy current loss. Since the iron core itself is a metal conductor, the electromotive force generated by the electromagnetic induction phenomenon will generate a circulating current in the iron core, which is an eddy current. Because there is eddy current flowing in the iron core, and the iron core itself has resistance, it causes eddy current loss.
3) Additional iron loss. The additional iron loss is not entirely determined by the transformer material itself but is mainly related to the structure and production process of the transformer.
The main reasons that usually cause additional iron loss are:
There are high-order harmonic components in the magnetic flux waveform, which will cause additional eddy current loss; due to the deterioration of the magnetic properties caused by mechanical processing, the loss will increase; in the core joints and the T-shaped area of the core column and the yoke The increase of local loss that occurs.
Since the no-load loss is an important parameter of the transformer, it only accounts for 20% to 30% of the total loss of the transformer. To reduce the no-load loss, the total core, unit loss, and process coefficient must be reduced. The main methods to reduce no-load loss are as follows:
(1) Adopt a high-permeability silicon steel sheet and amorphous alloy sheet. The thickness of an ordinary silicon steel sheet is 0.3～0.35 mm, the loss is low, and it can be 0.15～0.27 mm. At the same time, if the stepped stack is adopted, the iron loss can be reduced by about 8%.
Laser irradiation, mechanical indentation, and plasma treatment can make the loss of high magnetic silicon steel sheet lower. Amorphous alloy sheets and silicon steel sheets with a silicon content of 6.5% made according to the principle of rapid cooling have smaller eddy current losses than general high-magnetic silicon steel sheets.
(2) Reduce the process factor. The process loss coefficient is related to many factors such as silicon steel sheet material, whether the punching and shearing equipment is annealed, and the degree of clamping. The accuracy of cutting tools, reasonable installation, and adjustment of the punching and shearing equipment is also very important.
(3) Improve the core structure. The iron core is not punched, and glass adhesive tape is not bound. The end surface is coated with curing paint, and the alternate iron yoke is bound with high-strength steel tape. Non-magnetic steel plates are used for pull plates connecting upper and lower clamps on both sides of the stem.
The large-capacity iron core piece is not painted to improve the filling factor and cooling performance. The two yokes of the iron core are made into a solid, flat, and high-precision whole with strong pressure tooling and glue. Reducing the lap width of the core can reduce the loss. For every 1% reduction in the lap area, the no-load loss will be reduced by 0.3%.
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