Minimization of proximity losses in electrical machines with tooth-wound coils

Proximity losses are one of the main drawbacks in electrical machines with high rotational speed and electrical frequency. The reduction of proximity losses is usually pursued by adopting thin wires, which are twisted in the case of parallel connection. Twisting is a very effective solution for reducing proximity losses, but it also worsens the slot filling factor, heat dissipation, and dc resistance. This paper proposes an optimal twisting criterion that allows the minimization of the ac Joule losses due to parasitic circulating currents and reduces the number of twists and the length of the coils. The criterion applies to machines having tooth-wound coils and is validated by finite-element analysis and experimental results