Optimal Choice for Number of Strands
in a Litz-Wire Transformer Winding


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Plenary Paper Presented ad IEEE Power Electronics Specialists Conference, June 1997

Charles R. Sullivan
Thayer School of Engineering,
Dartmouth College,
Hanover, NH 03755-8000
chrs@dartmouth.edu
http://engineering.dartmouth.edu/inductor

Paper presented at the PESC '97, Technical Program, Plenary Session 1, Monday, June 23, 1997, St. Louis MO.

abstract---The number of strands to minimize loss in a litz-wire transformer winding is determined. With fine stranding, the ac resistance factor decreases, but dc resistance increases because insulation occupies more of the window area. A power law to model insulation thickness is combined with standard analysis of proximity-effect losses.

INTRODUCTION

SKIN EFFECT, PROXIMITY EFFECT, AND LITZ WIRE

DC RESISTANCE FACTORS

NUMBER OF STRANDS FOR MINIMUM LOSS

DESIGN EXAMPLES AND SUB-OPTIMAL STRANDING

EXPERIMENTAL RESULTS

CONCLUSION

ACKNOWLEDGEMENTS

APPENDIX
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