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Development of Ferromagnetic Metallic Glasses into Low Loss Power Transformer Cores


Floyd, Michael Cameron Dawley (2018) Development of Ferromagnetic Metallic Glasses into Low Loss Power Transformer Cores. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/Z9QF8R27.


Currently, 3% of energy losses in the U.S. electrical grid occur at power transformers. With a transition to Metglas, transformer efficiency could be increased, but is Metglas the best replacement material for power transformers?

With this in mind we develop a Fe-based metallic glass for its glass forming ability and soft magnetic properties. During this development we identify a redox reaction of boron oxide by Si during melt fluxing of the Fe-based glass, which promotes an unexpected exchange of Si and B in the alloy. Taking this reaction into account, a unique optimization strategy is implemented, enabling oxide purification of the melt coupled with a significant but predictable shift in composition. This leads to an optimized Fe-based glass demonstrating a global peak in glass forming ability. Following boron oxide fluxing in the high temperature melt, alloy with composition Fe57.5Co20.2Si10.2B2.05P10.05 transforms to Fe57Co19.2Si6.8B7.4P9.6, and increases its critical rod diameter from 1 mm to 5 mm. The alloy also demonstrates excellent soft ferromagnetic performance characterized by a magnetic saturation of 1.53 T.

While developing the above alloy, we also analyzed the effect of varying thickness of a Fe68Mo4Ni3Co5Si1P11.5C5B2.5 transformer core as a function of frequency to discover if there was a minimum in the losses. We did not find a single minimum, but found that the optimal thickness exhibits a logarithmic dependency on frequency. This dependence suggests the optimal thickness of a core ranges from 100−400μm, instead of in the < 50μm range currently used. These larger optimal thicknesses are unexpected if anomalous losses are not considered, but the dominance of the anomalous losses at low frequencies, or for thin samples, validates the need for thicker power transformers. While other amorphous metals and casting techniques will yield varying results, the logarithmic dependence on frequency and the 100−400μm optimal thickness range should be broadly applicable.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Bulk Metallic Glass; Amorphous Metal; Ferromagnetic; Flux; Soft Magnet
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Materials Science
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Johnson, William Lewis
Thesis Committee:
  • Johnson, William Lewis (chair)
  • Schwab, Keith C.
  • Demetriou, Marios D.
  • Greer, Julia R.
  • Faber, Katherine T.
Defense Date:29 September 2017
Non-Caltech Author Email:mfloyd19 (AT)
Record Number:CaltechTHESIS:10262017-091901955
Persistent URL:
Related URLs:
URLURL TypeDescription adapted for Chapter 1. adapted for Chapter 2.
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:10546
Deposited By: Michael Floyd
Deposited On:02 Nov 2017 18:12
Last Modified:04 Oct 2019 00:18

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