Contribution of End-Winding Proximity Losses to Temperature Variation in Electromagnetic Devices

This paper presents an investigation into proximity losses in end-windings informed from 3-D finite-element analysis of an ac power inductor. The proximity effect in winding conductors is a result of circulating ac currents caused by magnetic fields generated by nearby conductors. The calculated results confirm that the effects within the end-winding while significant are lower compared to those with the active length of the conductors. The common approach of predicting proximity losses using 2-D field analyses accounts for active length of the conductors only, and therefore, an end-winding correction factor is needed to obtain a more accurate estimate of loss. The theoretical prediction of losses within the inductor has been validated experimentally on a prototype inductor. A simple method to account for the interdependence of ac loss and temperature is presented and is shown to differ significantly from the well-known dc variation of resistance with temperature.