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, twisted in case of parallel connection. Twisting is a very effective solution to reduce proximity losses but also worsens slot filling factor, heat dissipation and DC resistance. This work proposes an optimal twisting criterion that allows to minimize the ac Joule losses but also reduces the number of twisting and the coils length. The criterion applies to machines having tooth wound coils and is validated by finite element analysis (FEA) and experimental results.