Uncertainty Analysis of Empirical AC Proximity Loss Methods for Low-Loss Windings

State of the art electric machines are designed to run at high operating frequencies to maximise deliverable power for their packaging volume. High frequencies increase the proportion of frequency-dependent AC losses and, if not mitigated, AC loss in the machine windings can be excessive. Multi-stranded transposed conductors such as Litz wires have superior AC loss characteristics though are difficult to model and empirical characterisation is important in determining performance at in-use operating frequencies. Two empirical approaches for characterising AC proximity losses in non-contact tests are developed by appraising their uncertainty based on standard methods. Both approaches are shown to have good agreement with widely used 1D analytical models of solid conductors based on Dowell’s formula. A similar analytical method describes losses in Litz conductors relatively poorly, highlighting the value in performing rapid and accurate experimental characterisation of these low-loss conductors. Areas for further improvement of the test system are highlighted by identifying the measured test variables which most significantly contribute to the measurand uncertainty.