Litz wire has been widely used in high-frequency electrical machines and transformers to minimize induced current loss and maintain high efficiency. Its heat dissipation capability can be a key design factor for high-power-density, high-frequency electrical machines. Although litz wire equivalent thermal conductivity has been studied, its transposition arrangement on heat dissipation enhancement is usually neglected. This article focuses on developing an analytical model to predict litz wire equivalent thermal conductivity including transposition effects. 3-D finite element models and hardware experiments are used to validate the proposed analytical model. Fast and accurate litz wire thermal conductivity prediction values can be obtained. The transposed and parallel arrangement effects on litz wire equivalent thermal conductivity are compared and discussed. This study shows that the transposition arrangement could improve litz wire heat dissipation capability by 10% to 30%, demonstrating that electrical machine power density can be potentially increased by up to 14%. The proposed method can advance winding design to push the boundaries of electrical machine power density.

Original languageEnglish (US)
Article number9333635
Pages (from-to)1440-1449
Number of pages10
JournalIEEE Transactions on Industry Applications
Issue number2
StatePublished - Mar 1 2021


  • Electrical machine
  • form-wound winding
  • litz wire
  • thermal conductivity

ASJC Scopus subject areas

  • Control and Systems Engineering
  • Industrial and Manufacturing Engineering
  • Electrical and Electronic Engineering


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