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


Note: This is an old version of this paper. Newer versions (in pdf format) are available at our new publications page


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

NEXT