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Magnetic properties and vibration characteristics of amorphous alloy strip and its combination

2019; Institution of Engineering and Technology; Volume: 13; Issue: 10 Linguagem: Inglês

10.1049/iet-epa.2019.0137

1751-8679

Daosheng Liu, Jiachen Li, Romaric Kammeugue Noubissi, Shihui Wang, Xiangdong Xu, Qianming Liu,

Surface Roughness and Optical Measurements

IET Electric Power ApplicationsVolume 13, Issue 10 p. 1589-1597 Research ArticleFree Access Magnetic properties and vibration characteristics of amorphous alloy strip and its combination Daosheng Liu, Corresponding Author Daosheng Liu daoshengliu@aliyun.com orcid.org/0000-0002-6306-6993 School of Electrical Engineering and Automation, Jiangxi University of Science and Technology, Ganzhou, 341000 People's Republic of China Electric Power Engineering, Chalmers University of Technology, Goteborg, S-412 96 SwedenSearch for more papers by this authorJiachen Li, Jiachen Li School of Electrical Engineering and Automation, Jiangxi University of Science and Technology, Ganzhou, 341000 People's Republic of ChinaSearch for more papers by this authorRomaric Kammeugue Noubissi, Romaric Kammeugue Noubissi School of Electrical Engineering and Automation, Jiangxi University of Science and Technology, Ganzhou, 341000 People's Republic of ChinaSearch for more papers by this authorShihui Wang, Shihui Wang School of Electrical Engineering and Automation, Jiangxi University of Science and Technology, Ganzhou, 341000 People's Republic of ChinaSearch for more papers by this authorXiangdong Xu, Xiangdong Xu Electric Power Engineering, Chalmers University of Technology, Goteborg, S-412 96 SwedenSearch for more papers by this authorQianming Liu, Qianming Liu School of Electrical Engineering and Automation, Jiangxi University of Science and Technology, Ganzhou, 341000 People's Republic of ChinaSearch for more papers by this author Daosheng Liu, Corresponding Author Daosheng Liu daoshengliu@aliyun.com orcid.org/0000-0002-6306-6993 School of Electrical Engineering and Automation, Jiangxi University of Science and Technology, Ganzhou, 341000 People's Republic of China Electric Power Engineering, Chalmers University of Technology, Goteborg, S-412 96 SwedenSearch for more papers by this authorJiachen Li, Jiachen Li School of Electrical Engineering and Automation, Jiangxi University of Science and Technology, Ganzhou, 341000 People's Republic of ChinaSearch for more papers by this authorRomaric Kammeugue Noubissi, Romaric Kammeugue Noubissi School of Electrical Engineering and Automation, Jiangxi University of Science and Technology, Ganzhou, 341000 People's Republic of ChinaSearch for more papers by this authorShihui Wang, Shihui Wang School of Electrical Engineering and Automation, Jiangxi University of Science and Technology, Ganzhou, 341000 People's Republic of ChinaSearch for more papers by this authorXiangdong Xu, Xiangdong Xu Electric Power Engineering, Chalmers University of Technology, Goteborg, S-412 96 SwedenSearch for more papers by this authorQianming Liu, Qianming Liu School of Electrical Engineering and Automation, Jiangxi University of Science and Technology, Ganzhou, 341000 People's Republic of ChinaSearch for more papers by this author First published: 15 July 2019 https://doi.org/10.1049/iet-epa.2019.0137Citations: 10AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Abstract Although the cores made with amorphous metal alloy have lowered no-load losses compared with the orientation silicon steel cores, a high cost and noise level are inevitable because the magnetostriction for amorphous metal alloy strip is larger than the ordinary one. This study mainly focused on the experimental systems and methods for magnetic properties measurement, vibration characteristics and noise level of amorphous alloy strip and combinations. The vibration characteristics and noise level of amorphous alloy composite strip were also studied. The influence of the annealing process on magnetic energy, vibration characteristics and noise level of amorphous alloy core were analysed in detail as well. All the testing results and analysis above are helpful for the transformer manufacturers, and they can replace the expensive amorphous alloy metal strip with the combinations to reduce the noise and cost of the cores. 1 Introduction Amorphous alloy metal core distribution transformer (AMDT) has been operating in the power grid for many years [1, 2]. For the purpose of building an energy-saving and environment-friendly society, most attention is focused on the no-load loss and noise of AMDT. AMDT has some unique advantages over a conventional silicon steel distribution transformer. AMDT has been adopted by the EU as a strategic guideline for improving energy efficiency, tackling global warming, and environmental protection, due to the potential in energy saving [3]. On the other hand, with the further improvement of industrialisation and urbanisation of the society, the urban population density is increasing, which makes the power distribution system closer to residential areas. Therefore, the audible noise of the power equipment, especially the one from a transformer, is of great concern. The studies have shown that the magnetostriction is the main cause of transformer vibration and noise [4]. By improving the manufacturing technology and optimising design, the low-loss characteristic of AMDT can be ensured. Reducing the noise of the AMDT core is the key to maintain a high-quality living environment. In order to improve the comprehensive performance of AMDT, the annealing processes of different types of amorphous alloy strips were investigated. According to the experiences from engineering practice, the magnetic materials selected as the core of the transformer should be with high saturation flux density, high magnetic conductivity, and low coercivity, thus the low loss, excitation power, and noise for a transformer could be obtained [5]. In addition, it is of great importance to master the magnetic characteristics of composite amorphous alloy strips during the design process. The practice has proved that the annealing process has a great influence on magnetostriction and corresponding magnetic characteristics. When the flux is distributed uniformly, the core loss of the transformer could be smaller. The authors of [6-12] literatures indicated that the magnetostriction is the main factor causing core vibration and audible noise. The variation of materials' magnetisation due to the applied magnetic field changes the magnetostrictive strain until reaching its saturation value. From the microscopic point of view, the magnetostriction of materials mainly comes from the coupling of the crystal field, spin orbit, and magnetic dipole interaction. From the macroscopic point of view, magnetostriction means that the magnetic domain inside the material will deflect under the external excitation condition, and the magnetic domain will generate small deformation along the magnetic field direction. The direction of the magnetic domain is also affected by external stress. When the magnetic material is subjected to stress, the direction of magnetic domain reversal will be deflected, which is opposite to the stress polarity overcoming the anisotropy of magnetic crystal. The differences in the distribution ratio, production process, existing impurities, storage, and impurities of amorphous alloy strip used in the power grid can lead to great differences in magnetic properties. Currently, in China, the mass production and application of the transformers with amorphous alloy strips are realised in several manufacturers such as Hitachi metals, Antai technology, and Qingdao Yunlu. In this study, the experimental subjects of amorphous alloy strips and their combination were produced by those manufacturers, and the magnetic energy, vibration, and noise characteristics were studied. Through the analysis and comparison of magnetic performance, vibration characteristics and noise level of ring core models made of different composite strips before and after annealing, several kinds of amorphous alloy strip combinations with better performance were obtained, which provided a new method for the AMDT noise reduction. 2 Principle theory 2.1 Magnetic loss The vibration caused by the magnetic field and mechanical coupling is very complex. For magnetic materials, external stress and lattice anisotropy of magnetic materials will influence the magnetostrictive coefficient. The magnetic domain reversal of the material will mainly be along with the direction of the vertical axis that is easy to be magnetised. The relationship between magnetostrictive strain λ and magnetisation intensity M can be described as [13] (1) where λs is the saturation magnetostriction and Ms is the saturation magnetisation intensity. In addition, the electromagnetic field energy method is used for the measurement of rotating core loss. According to Poynting's theory, the total loss Pc of samples can be calculated by using the following equation [14]: (2) where T is the magnetostrictive period of magnetic materials; ρm is the mass density of sample; H is the magnetic field strength; and B is the magnetic flux density. 2.2 Magnetostrictive vibration and noise levels In order to measure the vibration and noise level of the transformer core, the vibration acceleration of the core is proportional to magnetostriction λs [15]. By summarising and analysing a large amount of experimental and product test data, the theoretical calculation value of the AMDT sound pressure level is obtained as (3) where C1 is 45; Wt is the weight of the amorphous alloy core; C is the thickness of the amorphous alloy core (mm); D is the width of the amorphous alloy core (mm); N is the number of amorphous alloy core layers (row number); K1 is the correction coefficient of the magnetic flux density of the amorphous alloy core, 35–39; K2 is the saturation magnetic flux density; Bm is the magnetic flux density (T); K3 is 0.9–1.2 (when the frequency is 60 Hz). 3 Experimental equipment and programme 3.1 Magnetic measurement and procedure In this study, the static magnetic parameters of amorphous alloy materials were measured using the MATS-2010SD produced by Hunan Linkjoin Technology Co. Ltd. The main magnetic properties parameters are saturated magnetic flux density Bs, residual magnetic induction intensity Br, initial magnetic permeability μi, and coercivity Hc. In addition, the hysteresis loop of the amorphous alloy core was measured. The dynamic magnetic properties parameters of the amorphous alloy material, such as AC loss per unit mass Ps, excitation power Ss, the real part value of permeability μi, were measured by using an Iwatsu Sy8232 B-H analyser, which was produced in Iyazaki, Japan. The static magnetic characteristics of ring samples were determined by the impact method, while the dynamic characteristics of ring samples were determined by the voltammetry. The schematic diagrams of the DC static magnetic measurement and AC dynamic magnetic measurement are shown in Figs. 1a and b, respectively. Both DC and AC magnetic energy measurements were based on the induction principle. Fig. 1Open in figure viewerPowerPoint Magnetic properties measurement of the ring core (a) DC, (b) AC In Fig. 1, E is the DC power supply; R1 and R2 are adjustable resistors; N1 is the excitation coil; N2 is the test coil; G is the impact galvanometer; K is the control switch; M is the test sample; and RS is the sampling inductance. 3.2 Vibration properties measuring devices and procedure The multi-channel vibration and noise level measurement system is shown in Fig. 2. The stable voltage required for the experiment is provided by the voltage regulator. This vibration measuring system consists of two parts: the data acquisition unit and the data processing unit. The former is composed of an integrated circuit piezoelectric (ICP) vibration sensor, the latter is composed of an analogue-to-digital (A/D) sampling card and computer. Fig. 2Open in figure viewerPowerPoint Vibration characteristics and noise measurement of the ring core 3.2.1 Selection of vibration sensors The types of vibration signals for the transformer core and related parts are electromechanical with the vibration frequency from 10 to 2000 Hz and the amplitude from 0.5 to 500 μm. Currently, the vibration sensors are divided into three types: displacement sensors, speed sensors, and acceleration sensors. The displacement sensors cannot work with strong electromagnetic interference. The object of this study is the amorphous alloy transformer, which is designed according to the electromagnetic induction principle and will be interfered by a strong electromagnetic field under working or experimental conditions. In addition, the displacement sensors cannot be mounted on the surface of the object when measuring the vibration signals. Therefore, the displacement sensor is not suitable for the vibration measurement system. Though the speed sensor has the advantages of high sensitivity and voltage output, the amplifiers are easier to design as well, its frequency width is smaller and mainly <1000 Hz, which cannot meet the measurement requirement of the vibration signal of the transformer core. The acceleration sensors are classified into piezoelectric, strain and servo. Although the servo acceleration sensor is fast in low-frequency response, its frequency width is <500 Hz, which is not suitable for this experiment. Compared with the strain sensor, the weight of the piezoelectric sensor is smaller, mostly from 2 to 500 g. In addition, it has a higher resonant frequency and a wider frequency, which can be used according to the measurement requirements. In conclusion, the acceleration sensor is suitable for the transformer vibration measurement system. In order to convert the high-impedance signal measured by the sensor into a low-impedance signal, an amplifier needs to be preinstalled due to the high impedance of the pressure-sensitive element. The amplifiers could be divided into charge and voltage amplifiers. For the voltage amplifier, the vibration of this research object will affect the distributed capacitance of the cable connected with the sensors, and the distributed capacitance will affect the sensitivity of the amplifier. In addition, the length of the connecting cable between the amplifier and sensor is longer, which will also decrease the sensitivity of the amplifier. To overcome these disadvantages of piezoelectric sensors, ICP sensors were used in this study. The power supply of the sensor shares a cable with the signal transmission, and the output impedance is low. Usually, the ICP sensor consists of a sensor, ordinary double wire cable, and uninterruptible power supply. The ICP test system is shown in Fig. 3. Fig. 3Open in figure viewerPowerPoint Typical ICP testing system There are three kinds of effects for the piezoelectric acceleration sensors: longitudinal effect, transverse effect, and shear effect. Longitudinal effect type is the most commonly used, and the structure is shown in Fig. 4. Fig. 4Open in figure viewerPowerPoint Cross section of the longitudinal effect-type acceleration sensor If the mass of the inertial block is much less than the tested object, the inertial mass block will feel the same vibration as the sensor base during its working. The inertial mass is subjected to the inertial force opposite to the acceleration direction and at the same time the inertial force acting on the piezoelectric plate produces a direct proportion to the acceleration of the electric charge (4) where d33 is the coefficient of the piezoelectric sheet; m is the inertial mass of the block, kg; and a is the accelerated velocity, m/s2. Equation (4) indicates that the magnitude of the acceleration is reflected by the number of charges. The piezoelectric coefficient and the mass block can be used to determine the sensitivity of the sensors. The piezoelectric acceleration sensor can be simulated by a second-order system consisting of mass m; spring k; and damping c; as shown in Fig. 5. Fig. 5Open in figure viewerPowerPoint Second-order simulation system According to the second-order simulation system, the transfer function of frequency including amplitude frequency and phase frequency characteristic is shown in (5) and (6), respectively (5) (6) where is the relative damping coefficient; is the natural frequency of the sensor; ω is the angular frequency; , x0 is the displacement of the testing object; xm is the displacement of the sensor mass block; and is the deformation of the piezoelectric element. The sensitivity of the piezoelectric acceleration sensor is expressed as follows: (7) where ky is the elastic coefficient of the piezoelectric element. By putting (4) into (7), we obtain (8) By putting (8) into the equation of amplitude-frequency characteristic, the relation between the sensitivity of the piezoelectric acceleration sensor and the measured vibration frequency is (9) According to (9), the frequency response characteristics of a piezoelectric acceleration sensor can be obtained as shown in Fig. 6. When the vibration frequency of the measured object is far less than the natural frequency of the sensor, the relative sensitivity of the sensor is approximately constant (10) Fig. 6Open in figure viewerPowerPoint Frequency response characteristics of the acceleration sensor In the real measurement process, only 1/3–1/5 of the natural frequency of the sensor is generally taken as the upper limit of the vibration frequency, i.e. the flat section of the frequency response characteristic when it works. In this range, the sensitivity of the sensor is almost constant, and it will not change with frequency. The piezoelectric acceleration sensor is small in size, light in weight, large in stiffness, and its natural frequency usually reaches 30 kHz. While the useful signal frequency range of the transformer core vibration signal is up to 2000 Hz. Obviously, it can meet the needs of the measurement. In this study, the selected vibration sensor is ICP AD1000 with 0.2–8000 Hz measurement range and 1000 mV/g sensitivity. 3.2.2 Selection of other devices The noise meter used to measure sound pressure was commercial Fluk 945. Its measurement range is 30–130 dB and the resolution rate is 0.1 dB. According to IEC60076-10 Power Transformers Part 10, the noise sound pressure level is measured with Fluk945 0.3 m away from the contour of the testing object. An A/D data acquisition card with a universal serial bus interface was selected to collect and record the vibration signal of the testing object. The resolution of the acquisition card is 24 bits, and the maximum sampling frequency is 128 kHz. When the voltage is applied to the excitation coil, the sensors and noise meter start to collect the vibration signal and noise level, respectively. During the experiment, the PC records the vibration characteristics and the noise meter records the sound pressure level. In order to ensure the waveform is smooth and the frequency components will not omit after fast Fourier transform spectrum analysis, the selected sampling frequency is 32 kHz. 3.3 Testing cores and their combination samples In this study, three kinds of amorphous alloy strips and their combination, which are commonly used by most transformer manufacturers, were adopted as the transformer cores. All kinds of strips were represented by deferent alphabetic codes, and the combined strips were described with their respective alphabetic codes. More details are shown in Table 1. All samples were made into cylinder (or ring) shapes, as is shown in Fig. 7. The number of each strip in the mixed core is equal to half of the total. The main dimensions of core samples and composite cores are shown in Table 2. The core sample and combined core are annealed in the transverse magnetic field. The relationship between the added magnetic field direction and the sample is shown in Fig. 8, and the annealing process is shown in Fig. 9. Table 1. Amorphous strip and its composite material code Material Name Width, mm Number Unannealed Annealed 2065 SA1 142.24 A1 A2 1K101 142.24 C1 C2 AYFA 142.24 D1 D2 2065 SA1 + 1K101 142.24 A1 + C1 A2 + C2 2066 SA1 + AYFA 142.24 A1 + D1 A2 + D2 1K101 + AYFA 142.24 C1 + D1 C2 + D2 Table 2. Dimensions of core samples and composite cores Code H, mm A, mm B, mm Le, mm Se, mm2 M, g N1 N2 A1 142.24 64.32 62.3 199.84 67.185 96.4 51 51 C1 142.24 65.15 63.9 202.71 52.354 76.2 49 50 D1 142.24 63.52 64.2 200.65 60.805 87.6 53 49 A1 + C1 142.24 51.28 50 159.1 34.26 46.6 15 2 A1 + D1 142.24 53.4 48.5 160.1 49.99 68.4 16 2 C1 + D1 142.24 59.13 58 184 26.70 42 16 2 Fig. 7Open in figure viewerPowerPoint Ring (cylindrical) core diagram Fig. 8Open in figure viewerPowerPoint DC magnetic field and direction Fig. 9Open in figure viewerPowerPoint Annealing curve of amorphous alloy strip In Table 2, H is the height of the sample (mm); A is the outer diameter of the sample (mm); B is the inner diameter of the sample (mm); Le is the average circumference of the sample (mm); Se is the cross-sectional area (mm2); M is the sample mass (kg); N1 is the number of exciting coil turns; and N2 is the number of turns of the output coil. After being annealed, the stress in amorphous alloys caused by the rapid quench casting process is most likely to inhabit optimum magnetic properties in finished cores. In order to prevent the amorphous alloy strip from oxidation, the nitrogen and other protective gases should be filled during the annealing process. As shown in Fig. 9, line AB shows that the temperature in the furnace rises at a constant rate and the speed from ambient temperature to 300°C within 90 min. As shown in the line BC part, the temperature is stable at 300°C for the first heat preservation, and the time is 20 min to eliminate the temperature difference between the internal and the external of the amorphous strip. When the temperature in the furnace reaches 200°C, the 1400 A/m optimal transverse magnetic field is added. As shown in the line CD section, it takes 40 min to reach the best annealing temperature of 380°C after the first heat preservation. The line DE part shows that when the temperature is stable at 380°C, the second heat preservation will be made for 30 min. The line EF part shows that the temperature decreases after the second heat preservation. The transverse magnetic field will stop when the temperature of the iron base amorphous strip drops to 100°C. 4 Experimental results 4.1 Effect of annealing on static magnetic properties of amorphous alloy strip Under ambient temperature, the DC static magnetic characteristics parameters' testing and AC dynamic magnetic characteristics parameters' testing were conducted on unannealed amorphous alloy strips (A1, C1, D1), unannealed amorphous alloy composite strips (A1 + C1, A1 + D1, C1 + D1), annealed amorphous alloy strips (A2, C2, D2) and annealed amorphous alloy composite strips (A2 + C2, A2 + D2, C2 + D2), respectively. In Fig. 10a, the hysteresis loop of the amorphous alloy strip before annealing is approximately rectangular. In Fig. 10b, after annealing with the transverse magnetic field, the magnetic properties of the amorphous alloy strip converted into permanent magnetic permeability, and the shape of the hysteresis loop became longer. The main reason for the change of the hysteresis loop is that during annealing, some crystal grains are bound together due to the ferromagnetic coupling, which hinders the formation of single crystal grain magnetic anisotropy, and finally forms effective anisotropy, also known as domain anisotropy. In an ideal situation, many crystal grains combine to form a domain anisotropy due to the magnetic annealing. The transversely induced magnetic hysteresis is perpendicular to the direction of the vertical axis, so the hysteresis loop becomes narrower. Fig. 10Open in figure viewerPowerPoint Hysteresis loop of amorphous alloy cores (a) Before annealing, (b) After annealing From the comparison between Tables 3 and 4, it can be inferred that before annealing, the maximum magnetic permeability of the amorphous strip is small, the coercivity is high, and the soft magnetic properties are poor. After annealing, the structure of amorphous alloys tends to be metastable, the internal stress of amorphous alloys was largely released, and the soft magnetic properties were greatly improved. The annealing temperature of the soft magnetic amorphous alloy is between the Curie temperature and the temperature that the glass state starting to form. The annealing process can effectively reduce the internal stress, magnetic anisotropy and coercivity of the amorphous alloy. Hence, the soft magnetic properties of the amorphous alloy core were improved. Table 3. Magnetic properties parameters of core sample before annealing Core number Parameters μi, k μm, k Bs, T Br, T Hc, A/m Hs, A/m A1 0.9018 67.01 1.455 0.7009 5.127 80.6 C1 0.8939 31.74 1.542 0.473 6.152 80.2 D1 1.079 45.52 1.553 0.5497 4.693 80.3 Table 4. Magnetic properties parameters of core sample after annealing Core number Parameters μi, k μm, k Bs, T Br, T Hc, A/m Hs, A/m A2 5.08 39.88 1.46 0.3329 3.593 80.05 C2 4.99 48 1.371 0.3429 3.316 80.01 D2 3.961 41.49 1.329 0.3753 4.268 80.02 Fig. 11a shows that the magnetic hysteresis loop of the amorphous alloy composite strip is rectangular before annealing. Fig. 11b shows that the curve's shape becomes longer and narrower after annealing with a transverse magnetic field. The main reason for this change is that during the magnetic annealing process, the internal stress of the amorphous alloy was largely released and the soft magnetic properties were greatly improved, which were the same as the magnetic properties change of the amorphous alloy core sample in Fig. 10. Compared Fig. 10b with Fig. 11b, the maximum magnetic permeability and coercivity of the composite core were further reduced, and this is because two different materials are combined, the magnetic domain formed by the crystal grains bonded together are more isotropic under the condition of magnetic annealing. The transversely induced magnetic field is perpendicular to the longitudinal axis, which causes a longer and narrower magnetic hysteresis loop. Fig. 11Open in figure viewerPowerPoint Hysteresis loop of amorphous alloy composite cores (a) Before annealing, (b) After annealing From the comparison between Tables 5 and 6, it can be inferred that before annealing, the maximum magnetic permeability of amorphous composite strip is small, the coercivity is high, and the soft magnetic properties are poor. After annealing, the structure of amorphous alloys tends to be metastable, the internal stress of amorphous alloys was largely released, and the soft magnetic properties were greatly improved. Compared with Tables 3 and Table 4, the static magnetic characteristic of the composite strip after annealing will be improved further. Table 5. Magnetic properties parameters of composite strip before annealing Core number Parameters μi, k μm, k Bs, T Br, T Hc, A/m Hs, A/m A1 + C1 0.8831 45.83 1.429 0.6047 5.767 80.3 A1 + D1 0.8188 48.63 1.394 0.6218 6.045 80.6 C1 + D1 0.9193 35.49 1.419 0.5178 6.371 80.5 Table 6. Magnetic properties parameters of composite strip after annealing Core number Parameters μi, k μm, k Bs, T Br, T Hc, A/m Hs, A/m A2 + C2 1.614 77.95 1.156 0.6733 3.312 80.1 A2 + D2 2.476 70.76 1.205 0.6737 4.002 80.05 C2 + D2 1.727 58.333 1.18 0.6448 4.514 80.05 4.2 Effect of annealing on dynamic magnetic properties of amorphous alloy strip It can be seen from Fig. 12a that the dynamic hysteresis loop of the amorphous alloy strip is rectangular before annealing. As is shown in Fig. 12b, the curve shape becomes longer and narrower after annealing with a transverse magnetic field. Its change law is consistent with that of static characteristics. Fig. 12Open in figure viewerPowerPoint Dynamic hysteresis loop of amorphous alloy strip at 50 Hz (a) Before annealing, (b) After annealing It is shown in Tables 7 and 8 that the excitation power Ss (VA/kg) of A1, C1 and D1 of amorphous alloy strip samples after annealing decreased by 1.25, 0.162 and 0.337 VA/kg, respectively, compared with that before annealing. The no load loss Ps (W/kg) decreased by 0.035, 0.005 and 0.009 W/kg, respectively. The coercivity Hc (A/m) decreased by 1.644, 0.324 and 0.78 A/m, respectively. The remanence Br (T) decreased by 0.333, 0.053 and 0.022 T, respectively. The area of the hysteresis loop shows that the soft magnetic properties of the annealed amorphous alloy strip are optimised. In addition, the saturation magnetic flux density Bs also increased. Table 7. Dynamic magnetic properties parameters of amorphous alloy strip at 50 Hz before annealing Core number Parameters Hz Ss, VA/kg Ps, W/kg Br, T Bm, T Hc, A/m Hm, A/m A1 50 2.719 0.2514 0.6924 0.8049 11.17 79.77 C1 50 1.832 0.165 0.4686 0.7049 9.924 79.06 D1 50 1.854 0.1939 0.5363 0.73 10.28 80.38 Table 8. Dynamic magnetic properties parameters of amorphous alloy Strip at 50 Hz after annealing Core number Parameters Hz Ss, VA/kg Ps, w/kg Br, T Bm, T Hc, A/m Hm, A/m A2 50 1.46 0.2619 0.