Effect of the Annealing Temperature on Magnetic property for Transformer with Amorphous Core

Transcription

1 Effect of the Annealing Temperature on Magnetic property for Transformer with Amorphous Core a Chang-Hung Hsu a, b, Yeong-Hwa Chang Electrical Engineering, Chang Gung University, Tao-Yuan, Taiwan b Electric Machine, Fortune Electric Ltd, Co., Tao-Yuan, Taiwan chshiu@fortune.com.tw a Abstract: - This paper presents the results of experimental investigations of annealing elevated, magnetic properties and their application with amorphous SA1 Cores. The phenomenon of two exothermic peaks correlated with the crystallization behavior was examined by means of differential scanning calorimetry (DSC). The magnetic phase transition process was investigated by thermogravimetric analysis (TGA). The magnetic properties were measured for samples annealed at different temperatures ranging from 330 to 470. For the amorphous alloy SA1 core, the annealing temperature is set at 360 for two hour in an air atmosphere, the lowest core loss were obtained. During the annealing process, a DC current driven magnetic field is applied to further improve the magnetic properties. Finally, at the same specifications and rated power, experimental results of the magnetic loss are presented for the amorphous alloy SA1 core transformer and traditional silicon steel core transformer. It can be seen that the amorphous core transformer can provide better performance in the aspect of core loss and exciting power. Key-Words: - Amorphous materials; Annealing; Curies temperature; Core loss; Exciting power; Transformer 1 Introduction Application of the Fe-based amorphous alloy is consider material of the low loss, the lights of reduction of gas discharge and preservation of the environment in industry. Due to the progress of physical and magnetic techniques, the soft ferromagnetic materials have many excellent properties of high saturation magnetic flux density, high permeability and low losses. In [4-6], for amorphous alloy core, being capable of the magnetization saturation induction, hyteresis loss and noise, is suitable for transformer application in industry. Between 320 and 350 of annealing temperature, the different annealing procedure relate with noise variation for amorphous alloy is discussion in [7]. In additional, the transformers were fabricated by amorphous SA1 cores combined with superconductivity winding in [8, 9]. Application aspect of the transformer survey in industry, it is certainly that not only the winding of the superconductivity stability, but also focused on core loss performance for amorphous core was also concerned. Therefore, there are many unavoidable disadvantages for amorphous materials can be understood. It is obvious that the alloy have exist difficultly the manufacturing procedure, such as low saturation induction, high brittleness, high hardness, low core lamination staking factor for amorphous alloy. Both of physical characteristic variations and annealing elevated temperature control directly effect on magnetic property of the amorphous alloy were acquired. In [11, 12], a 1kVA transformer of Fe-based amorphous alloy Fe 78 Si 9 B 13, to achieve knowing the material magnetic property, the crystallization temperature, Curies temperature and material structure changed was detected by DSC TGA and XRD. The annealing temperature is set to be 380 with an applied DC magnetic flux density 800A/m, so that the best core crystallization point can be obtained. Finally, following above measured results of magnetic property, it can be improving that amorphous alloy suitable manufacturing transformer core. However, until now, for Fe-based amorphous alloy SA1 material, the aspect of the different annealing temperature effect on material structure change, magnetic loss and saturation induction variation were not discussed recently. Therefore, this paper presents the transformer core of the annealing elevated temperature factor, such as material magnetic property and their application. The aim of this paper is organized as follows. In section 2, the material magnetic property of Fe-based amorphous SA1 alloys are discussed in detail. In section 3, to introduced magnetization relate with different annealing temperature with amorphous core are analyzed. Section 4, Application of the transformer core was manufactured by amorphous material SA1, compared conventional silicon steel ISSN: ISBN:

2 core and discussing in detail. The conclusion is given in section 5. 2 Materials Properties Analysis In order to found out the crystallization processes occurring in the sample of amorphous alloy, differential scanning calorimetry (DSC) was performed in Fig. 1. The DSC scans is recorded at 5 /min, DSC results show two exothermic peaks at 457 and 477 which clearly represent two crystallization temperatures corresponding to activation energies of 26.84J/g and 72.51J/g, respectively Fig.2 The measured results of the ribbon Curie temperature. Fig.1 The measured results of the ribbon crystallization and exothermic peaks. Differential scanning calorimetry (DSC) is considered to be a convenient and relatively accurate method for measuring the thermal phase transition of materials. In particular, it gives effective observations of the crystallization of amorphous alloys. However, sometimes it can also be used to measure the Curie transition temperature Tc. The magnetic Curie transition involves a small change in enthalpy, and this heat flow results in a detectable peak. When magnetic material under heat treatment procedure, it is clear that physical phenomenon of the annealing temperature achieving Curies temperature (Tc) can be observer, which the material of magnetic property will be change form ferromagnetic to paramagnetism. At this time, the magnetization intensity will be slowly disappearing. The Curie temperature (Tc) of the SA1 materials was measured by TGA. Therefore, according to measured results in Fig. 2, the Curies temperature of the amorphous SA1 material was occurred at Magnetization Relate with Different Annealing Temperature Due to amorphous ribbon has complicated process be a core, because it was fabricated necessary procedure, such as ribbon cutting, rolling up and formed a toroidal core. Therefore, both of the stress of ribbon and atomic arrange with different direction effect on magnetic property of the ribbon were obtained. Before execution of annealing process, there is obviously that measured results of the lower saturation induction and lower core loss compared with annealed core were obtained. Therefore, the core manufacturing with annealing is necessary process. The ribbon existing high stress was fabricated by rapidly solidification phenomena. The final object is release the core stress effecting with magnetic response. In order to acquire the soft magnetic property for amorphous alloy, the core loss, exciting power and magnetic anisotropic condition was reduced by annealing process. It was hopefully that lowest core loss for core was desired. The measured results of the hysteresis loop for amorphous alloy of the magnetic material and silicon steel was shown in Fig. 3. Owing to a few advantages for amorphous alloy compared with silicon steel material, such as higher permeability, lower core loss and lower saturation induction property has been presented. This paper presents experimentation condition for amorphous ribbon, it was considerate to observer magnetic properties variation of Fe-based amorphous core annealing temperature under 330, 360, 390, 430 and 450, 470 in argon atmosphere. The measured results of the hysteresis loop for amorphous alloy with different annealing temperature was shown in Fig. 4. Therefore, ISSN: ISBN:

3 measured the core of the saturation induction was only achieved 1.0 (T). The measured results of the core compared with core annealed at 360, the magnetic loss was higher than five times, and saturation induction was only 0.8 (T). If core of amorphous alloy is perform under suitable annealing process. It will be release the residual stress caused by rapidly solidification procedure. At this time, the core of saturation induction will be rapidly promoted, 1.56 (T). The measured results of the core of hysteresis loops relative with different annealing temperature was shown in Fig. 6. The hysteresis loop variation respects with different annealing temperature were obtained. Setting annealing temperature higher than 390, the material of structure were occurred gradually strong crystallization phenomenon. It was obviously effect material of the magnetic loss. To observer both of saturation induction and permeability was also obviously dropped. However, measured magnetic characteristic results between 430, 450 and 470, both of core loss and exciting power will increasing higher than 3 to 5times. Observing the low induction and low permeability, it is easily that material of the crystallization and Curies reactive by weakness properties of the paramagnetic materials were observed. To increase the annealing temperature at 430, the measured results of saturation induction decreased to 1.2 (T) and coercivities increased to 8A/m were also obtained. Beside, the amorphous ribbon has increased the annealing temperature up to 450; the crystallization formation structure was completely appearing. In this time, the magnetic property was almost disappeared, this measured results was corresponding with crystallization point reaction in Fig. 1. Consequently, in order to keeping the high magnetic flux density and high permeability properties for core of the transformer, it should be avoid high annealing processing induced weakness magnetization phenomenon. So, the reference guideline for improving the core loss can be desired by extension of annealing sock times than normal process. In Fig. 5, the measured results of the core loss depend on induction, when induction higher than 1.2(T), it can be observer that the core loss will be higher than 0.7(W/kg). Further more, the exciting power depend on induction was shown in Fig. 6, it was easily observer higher exciting power, 0.4(VA/kg). Fig.3. The measured results of hysteresis loop, the Fe-based amorphous core before annealing, after annealing and silicon steel core. Fig.4. Temperature dependence of magnetization for amorphous cores annealed at different temperatures and time durations. Fig.5. The measured core losses of SA1 core respect with different annealing temperatures ISSN: ISBN:

4 Fig.6. The measured exciting power of SA1 core respect with different annealing temperatures Fig.7. The three-phase five-legged 1850 kva amorphous core transformer. 4 Transformer manufacturing and testing The annealing temperature control is crucial for the manufacturing of amorphous materials. If the annealing temperature is too high, it will cause localized partial crystallization, and the resulting magnetic crystalline anisotropy will tend to increase the core loss. Otherwise, if the anneal temperature is too low; the residual stress is not adequately relieved. From experimentation results, for the amorphous alloy SA1 ribbon, the annealing temperature is set at 360 for two hour in an air atmosphere. During the annealing process, a DC current driven magnetic field is applied to further improve the magnetic properties. In this paper, the magnetic field density 800 A/m is utilized to reduce the core loss. According to experimentation results, it can be found that to obtain the lowest core loss the annealing temperature is of 360±10 for the amorphous alloy SA1 core. The amorphous alloy core of the transformer was fabricated in Fig. 7. The measured core loss and exciting power related to magnetic induction are shown in Fig. 8 and Fig. 9, it can be seen that the core loss of SA1 core transformer is less than the value of silicon steel transformer with each designated magnetic flux density Bm. In Fig. 3, the saturated flux density of SA1 transformer is about 1.56 (T), while the saturated flux density of silicon steel transformer is about 2.0 (T). It is notice that the exciting power of SA1 transformer is less than that of silicon steel transformer with magnetic flux density Bm less than 1.4 (T). To achieve better efficiency by using the fabricated SA1 amorphous alloy core transformer, it is suggested to follow the observation that the magnetic flux density is less than 1.4 (T). Fig.8. The measured core losses of SA1 core transformer and silicon steel transformer. Fig.9. The measured exciting power responses of SA1 core transformer and silicon steel transformer. 5 Conclusion This paper presents the results of experimental investigations of annealing elevated, magnetic properties and their application with amorphous SA1 materials. The phenomenon of two exothermic peaks correlated with the crystallization behavior was ISSN: ISBN:

5 examined by means of differential scanning calorimetry (DSC). The magnetic phase transition process was investigated by thermogravimetric analysis (TGA). For the amorphous alloy SA1 core, the annealing temperature is set at 360 for two hour in an air atmosphere, the lowest core loss were obtained. To investigate the performance of magnetic properties, a 3-phase wound amorphous-cored transformer with capacity 1850kVA is constructed. Experimental results illustrate that the proposed core can provide better performance of lower core loss, exciting power and noise than the conventional counterpart. References: [1] R. Hasegawa, Applications of amorphous magnetic alloys, Materials Science and Engineering A, Vol , No.1-3, 2004, pp [2] R. Hasegawa, Applications of amorphous magnetic alloys in electronic devices, Journal of Non-Crystalline Solids, Vol.287, No.1-3, 2001, pp [3] R. Hasegawa, Present status of amorphous soft magnetic alloys, Journal of Magnetism and Magnetic Materials, Vol , No.2, 2000, pp [4] R. Hasegawa, D. Azuma, Impacts of amorphous metal-based transformers on energy efficiency and environment, Journal of Magnetism and Magnetic Materials, Vol.320,No.20, 2008, pp [5] R. Hasegawa, Advances in amorphous and nanocrystalline magnetic materials, Journal of Magnetism and Magnetic Materials, Vol.304, No. 2, 2006, pp [6] Y. Ogawa, M. Naoe, Y. Yoshizawa, R. Hasegawa, Magnetic properties of high Bs Fe-based amorphous material, Journal of Magnetism and Magnetic Materials, Vol.304,No.2, 2006, pp. e675-e677. [7] D. Azuma, R. Hasegawa, Audible noise from amorphous metal and silicon steel-based transformer core, IEEE Transaction on Magnetic, Vol.44, No.11, 2008, pp [8] C. Chen, Y. J. Yu, L.Y. Xiao, Q.L. Wang, C. Wooho, K. Keeman, B. Sungkeun, The magnetic properties of the ferromagnetic materials used for HTS transformers at 77 K, IEEE Transaction Applied Superconductivity, Vol.13, No.2, 2003, pp [9] Y. Wang, X. Zhao, J. Han, H. Li, Y. Guan, Q. Bao, L. Xiao, L. Lin, X. Xu, N. Song, F. Zhang, Development of a 630 kva three-phase HTS transformer with amorphous alloy cores, IEEE Transaction Applied Superconductivity, Vol.17, No., 2007, pp [10]H.W. Ng, R. Hasegawa, A.C. Lee, L.A. Lowdermilk, Amorphous alloy core distribution transformers, IEEE Proceedings, Vol.79, No.11, 1991, pp [11]B.A. Luciano, C.S. Kiminami, An amorphous core transformer: design and experimental performance, Materials Science and Engineering A, Vol , No.15, 1997, pp [12]B.A. Luciano, M.E. de Morais, C.S. Kiminami, Single phase 1-kVA amorphous core transformer: design, experimental tests, and performance after annealing, IEEE Transaction on Magnetic, Vol.35, No.4, 1999, pp [13]X.F. Li, K.F. Zhang, G.F. Wang, W.B. Han, Plastic deformation behavior of amorphous Fe 78 Si 9 B 13 alloy at elevated temperature, Journal of Non-Crystalline Solids, Vol.354, No.10-11, 2008, pp [14]Y.C. Niu, X.F. Bian, W.M. Wang, G.H. Li, S.F. Jin, Q. Jia, On the distinct tensile flow of amorphous Fe 78 Si 9 B 13 alloy at 430 C during continuous annealing, Journal of Alloys and Compounds, Vol.462, No.1-2, 2008, pp ISSN: ISBN: