Eddy-Current Effects In Magnetic Design (Part 5): Winding Design Optimization

Focus:

Dowell’s equation provides a graphic way of determining winding loss for a given wire size and number of layers. Leveraging this equation, this part addresses the problem of how to optimize wire size in transformers and coupled inductor designs to achieve minimum winding resistance. Given the two winding design parameters, penetration ratio ξ [Xi] and number of layers, M (with frequency, f given), the winding design goal is not to minimize F[sub]R in itself but to minimize winding loss, (P bar[sub] w of Xi). To achieve this goal, we will transition from F[sub]R to F[sub]r, which is proportional to winding loss. Whereas F[sub]R is the resistance ratio with constant wire size and varying frequency, F[sub]r instead has constant frequency with varying wire size. We can thereby find the optimal wire size using F[sub]r. Ultimately, we will find there are two possible solutions for minimizing eddy-current effects—a low-ξ solution involving a smaller wire size and a high-ξ solution involving a larger wire size. Each solution serves to minimize the contribution of eddy-current effects to winding losses, but each will be applicable under different winding requirements and operating conditions.

What you’ll learn:

• How to use Dowell’s equation to optimize selection of wire size for minimum winding resistance in transformers and coupled inductors

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Author & Publication:

Dennis Feucht, Innovatia Laboratories, Cayo, Belize, How2Power Today, Feb 17 2017

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