PROSPECTS FOR THE USE OF AMORPHOUS MAGNETIC MATERIALS TO OPTIMIZE MAGNETIC LOSSES IN ASYNCHRONOUS MACHINES

ABSTRACT

The article analyzes the magnetic losses in the stator and rotor part of an asynchronous electric machine. As a result of these analyzes, the prospects for the use of amorphous magnetic materials for optimization of losses are shown. The article also discusses the power loss in induction motors when using amorphous magnetic materials.

АННОТАЦИЯ

В статье анализируются магнитные потери в статорной и роторной части асинхронной электрической машины. В результате проведенного анализа показаны перспективы использования аморфных магнитных материалов для оптимизации потерь. В статье также обсуждаются потери мощности в асинхронных двигателях при использовании аморфных магнитных материалов.

Keywords: amorphous alloy, amorphous magnetic material, magnetic losses.

Ключевые слова: аморфный сплав, аморфный магнитный материал, магнитные потери.

Electric machines are an important component of the electric drive of production mechanisms and generation systems, consuming up to 40% of the world's electricity. Therefore, the task of increasing the energy efficiency of production processes cannot be solved without the use of appropriate electrical machines of a high energy efficiency class (energy efficient electrical machines).[1] In electrical machines, electromechanical energy conversion occurs with the obligatory conversion of part of electrical energy into heat. Since this part of the energy is lost in the conversion process, it is customary to call it losses, and the ratio of useful work to expended work is called the efficiency. Losses in its individual parts must also be known to determine the temperature in them, which affects the calculation of the dimensions and geometry of the main structural units electrical machines. Losses in electrical machines are divided into main and additional. The main losses include electrical losses (copper losses), magnetic (steel losses) and mechanical losses. Its depend on the steel grade, the thickness of the magnetic core sheets, the frequency of magnetization reversal and induction. In the rotors of synchronous machines, the current frequency in the nominal mode is small:

₂ =s_{n 1}                                                                         (1)

where s_n is the nominal slip;

₁  - stator current frequency, Hz.

Magnetic losses in most machines are independent of the load and are permanent losses. Usually this is an idle loss. Magnetic losses P_m in an induction motor are caused by hysteresis losses and eddy current losses occurring in the core during its magnetization reversal. The magnitude of the magnetic loss is proportional to the frequency of magnetization reversal

Р_м = f ^β                                                                              (2)

where β = 1.3 ÷ 1.5.

The following table shows the different power wastes in electric machines.[2]

Table 1.

 Distribution of losses in a four-pole asynchronous motor

As can be seen from the table above, 15-25% of the power losses in asynchronous machines account for magnetic losses. These magnetic losses in asynchronous machines depend on the type and parameters of the magnetic material used. Modern types of high-conductivity copper and aluminum coils can be used to reduce electrical losses in the stator and rotor. The magnetic materials currently used are not enough to reduce the magnetic losses in an electric car. Therefore, the use of magnetic materials made of amorphous alloys to minimize magnetic losses is one of the promising areas. Magnetic materials made of amorphous alloys began to be used in transformers instead of electrical steel.

Currently, high-frequency ferromagnetic modules are used in various fields, for example, in power supplies for technological equipment, such as induction installations, dielectric installations. heating, electrotechnical devices for mechanical material processing blanks for powering high-speed electric motors, etc. [3]  The use of modern magnetic materials - amorphous or nanocrystalline alloys will make it possible to get rid of the listed disadvantages, namely: to increase the efficiency of the applied installations, to reduce their weight and dimensions, which is associated with higher indicators of such materials, such as: saturation induction, specific magnetic losses at high frequencies. To confirm the effectiveness of the use of amorphous or nanocrystalline alloys, the authors performed calculations for a number of high-frequency ferromagnetic modules with magnetic cores made of various materials. Table 1 summarizes a number of the obtained parameters of the designed matching high-frequency transformer with a magnetic core made of nanocrystalline alloy GM 414 for a power supply for induction installations.[2]  Amorphous alloys have high strength and hardness (up to 1000 HV). At the same time, most strip samples of amorphous alloys can be bent and unbent without fear of their destruction; however, the degree of deformation during tensile testing is very small, because the sample undergoes highly localized shear deformation. Residual bending angle after bending of the sample by 180º is taken as a measure of plasticity of amorphous alloys. Tests indicate that amorphous alloys are quite ductile. It was believed that the structure of amorphous bodies is isotropic, since there is no crystallographic anisotropy. However, the study of the properties of amorphous alloys showed that they have magnetic anisotropy. The magnetic anisotropy of amorphous alloys is associated with the macroscopic anisotropy of the structure, which occurs during the preparation of amorphous alloys by all methods immediately before glass transition, when the viscosity increases sharply, causing shear stresses and deformations. In this case, pairs of atoms or their groups are arranged in accordance with the direction of deformation due to differences in the forces of chemical interaction and sizes. Anisotropy is also induced by internal stresses formed during glass transition. The magnitude of the magnetic anisotropy can be significantly reduced or changed by thermal (annealing), thermomagnetic or thermal treatment with the imposition of mechanical stresses. In general, amorphous alloys achieve very high characteristics for soft magnetic materials:

- high values of magnetic permeability;

- low coercive force;

- sufficient saturation magnetostriction, adjustable over a wide range of values;

- high resistivity;

- low coefficient of temperature dependence and low losses for hysteresis and eddy currents (3-5 times lower than the best crystalline alloys).

According to the data, amorphous alloys also have increased corrosion resistance, high resistance to adhesive wear. However, amorphous alloys have a number of significant disadvantages that complicate their use and make their use not entirely promising. The main disadvantages include:

- extreme fragility after heat treatment;

- high hardness, which makes cutting difficult;

- small thickness of the tape (up to 50 microns), which makes it almost impossible to mix;

- large unevenness of the tape thickness over the section, which significantly reduces the effective section of the elements of magnetic systems;

- high sensitivity to stresses, which is extremely undesirable in the case of using an amorphous alloy as a magnetically soft material.[3]

References:

1. Шумов Ю.Н., Сафонов А.С. Энергосберегающие электрические машины, «ЭЛЕКТРИЧЕСТВО» № 4/2015.
2. Валюшка А.О., Иода Д.Н.  Потери мощности и кпд асинхронных двигателей, Материалы 64-й научно-технической конференции студентов, магистрантов и аспирантов (апрель 2008 года).
3. Павленко Т.П.  Аморфные сплавы и возможность их применения в блоках полупроводниковых расцепителей автоматических  выключателей, журнал Електротехніка і Електромеханіка. 2007. №5.