New Analytical Model for Calculating HF-Losses in Litz Wire Regions Located Outside the E/U-CoreWindow of Transformers

Litz wire is essential for reducing high-frequency losses in medium frequency transformers, which are built often with ‘E’ or ‘U’ shaped cores. Many analytical models focus only on the winding section inside the core window, where the winding is completely enclosed by the core. The losses of the winding section outside the core window are not determined separately. This paper compares the losses of both winding sections and provides an accurate and fast loss model for the winding section outside the core window. The error of the model is less than 5%, which is much smaller than the 1D field model (up to 30%). Moreover, to compute the total winding losses the model requires about 90 µs, which is comparable to the time consumed by the 1D field model (72 µs on a standard laptop with a 4.8GHz,4-core CPU and a 16GB RAM).