Magnetic Materials for Current Transformers

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Proceedings of IBIC2013, Oxford, UK MOPF24

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Beam Charge Monitors and General Diagnostics 263 Copyright MOPF24 Proceedings of IBIC2013, Oxford, UK

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%DU NKDXVHQ(IIHFW %DU NKDXVHQ1RLVH The Barkhausen Effect is a physical phenomenon Barkhausen Noise tests were performed following the which is manifested as a series of jumps in magnetization setup described in [5] for all the materials, but using a of ferromagnetic material when exposed to a varying triangular current for the driving solenoid. magnetic field. Surrounding the sample by a secondary coil, the induced voltage can be transformed into acoustic Figure 1 shows a comparison of the BN for cobalt- noise, from which the term Barkhausen Noise (BN) based amorphous materials. What can be seen is the derives [5]. voltage induced in the secondary coil surrounding the magnetic sample while it is subjected to the triangular This effect is often used as a non-destructive test to current. Time zero indicates when the pulse¶V YDOXH LV check changes in microstructure (grain boundaries, zero volts. As can be seen, most of the BN occurs around -3.0) dislocations, inhomogeneities, etc.) and stress this region, and drops to zero when the sample is configurations of materials. It is because of this, that this saturated. It has been observed that there is not a significant difference between them.

(CC-BY technique offers a good overview of changes in magnetic domains. 3.0 It is clear that the BN influences the transformer ution performance and its resolution [6], therefore it is an interesting characteristic to study to see the effect of the

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Commons e v 6XP PDU\RI0DWHULDOV8VHG For this study, the materials used were iron-based eati amorphous and nanocrystalline alloys and cobalt-based Cr amorphous alloys. The iron-based alloys were purchased cc from Qinhuangdao Yanqin Nano Science & Technology

— Figure 1: Barkhausen Noise response for amorphous Co., Ltd (http://www.yanqin.com), and the Cobalt-based cobalt-based materials (Nanoamor in green, Metglas in oW were purchased in Nanostructured & Amorphous red and VAC in blue).

AC Materials (Nanoamor), Inc. (http://www.nanoamor.com), J Vacuumschmelze GmbH & Co. KG However, Figure 2 shows the difference between the by (http://www.vacuumschmelze.de) as VC 6025 G40 and iron-based amorphous and nanocrystalline and the Hitachi Metals Europe GmbH (http://www.metglas.com) Vacuumschmelze materials. As can be seen, the iron- 2013 as 2705M.

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ISBN 978-3-95450-127-4

VAC material, which can be observed from the existence IXUWKHUDQQHDOLQJWHVWVVKRXOGQRWEHSHUIRUPHGRQWKHVH of BN throughout the measurement. This means that the PDWHULDOV WR IXOO\ H[SORUH WKH SRWHQWLDO PDJQHWLF samples with more and higher BN signal will have an SURSHUWLHVWKDWFRXOGEHDFKLHYHG XQGHVLUDEOH HIIHFW RQ WKH WUDQVIRUPHU¶V SHUIRUPDQFH DQG should be a factor to take into account when choosing the FRUH¶VPDWHULDO

Figure 3: B-H curve for iron-based nanocrystalline in red and iron-based amorphous alloys in blue.

Figure 2: Barkhausen Noise response for iron-based amorphous alloy in green, iron-based nanocrystalline $QQHDOLQJ7HVWVDQG0HDVXUHPHQWV alloy in red and VAC 6025 in blue. First annealing tests were performed under vacuum at 250 degrees Celsius during one hour. A Sol-Gel solution was poured over the cores in order to create an insulating 0 DJQHWLF3URSHUWLHV layer of magnesium oxide (MgO) as described in [4]. In order to measure the magnetic properties of the Before and after the treatment, magnetization curves were materials, an impedance analysis and a study of the B-H measured at 200 Hz from wound toroids. This curve was performed. The impedanec of the sample were measurement also enables the calculation of the measured and permeability was calculated from the maximum permeability and has been used to cross-check inductance of the measurement. For this purpose, cores of the one calculated by impedance analysis. external diameter of 45 mm and section of 10 mm x 10 -3.0) mm were wound for testing. Table 2 shows the maximum permeability measured for each material. (CC-BY 3.0 7DEOH3HUPHDELOLW\6XPPDU\

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9$&* e v 0HWJODV0 Figure 4: B-H curve before (in blue) and after annealing eati (in red) for VAC 6025. Cr

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[1] P. Odier, DCCT Technology Review, Workshop on DC Current Transformers and Beam-Lifetime Evaluations, Lyon, p. 3, December 2004, http://inspirehep.net/record/672655 [2] G. Bertotti, Hysteresis In Magnetism. (San Diego: Academic Press 2008) [3] K.Unser, Beam Current Transformer with DC to 200 MHz Range, Particle Accelerator Conference, Washington D.C., (1969) [4] S.H. Lim et al., Effects of Surface Coating by Sol-Gel Process on the Magnetic Properties of a Co-Based Amorphous Alloy. IEEE Transactions on Magnetics 13, N. Figure 5: B-H curve before (in blue) and after annealing 6, (1995) [5] D. Spasojevic, S. Bukvic, S. Milosevic and H.E. Stanley, (in red) for Nanoamor. Barkhausen noise: Elementary signals, power laws, and scaling relations. The American Physical Society 54, The study on the insulation proved that the technique (1996) used to create the MgO layer was not good enough and [6] P. Kottman, Theoretical and Experimental Investigation of there was no significant difference between the non- Magnetic Materials for DC Beam Current Transformers. insulated and the insulated cores. The technique to use the PS/BC/Note 97-06 Sol-Gel method should therefore be researched further and be compared to the insulation given by 'XSRQW70 .DSWRQ

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The iron-based alloys (both amorphous and nanocrystalline) have a maximum complex relative permeability which is too low for the characteristics sought and a coercive field which is too high. The tests

-3.0) performed so far on the cobalt-based materials show good potential characteristics in order to make full cores for &(51¶VFXUUHQWWUDQVIRUPHUV

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3.0 With three very good candidates, the annealing process should be further studied in order to verify how the different B-H curve shapes affect the response on the ution transformers. In addition to this, the insulation should be further studied, by improving the Sol-gel method Attrib technique and comparing to DupontTM Kapton® insulation. Both annealing possibilities, with magnetic field and conventional heating, should be studied in order to achieve the best magnetic properties for each Commons

e transformer. v eati $&.12:/('*0(176 Cr cc The authors would like to acknowledge Hansjörg Reeg — (GSI) for providing the winding machine for the toroids

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