Air-cooled large turbine generator with multiple-pitched ventilation ducts

On the air-cooled turbine generators, windage loss is the substantial factor of generator losses. One solution for the windage loss reduction is to minimize the amount of coolant air with the multiple-pitched ventilation ducts in the stator core. However, non-uniform duct distribution leads to the circulating currents in the stator bar strands which increase coil losses and cause significant distribution of strand loss. This paper presents circulating currents due to multiple-pitched ventilation ducts and some schemes to reduce the circulating current loss, such as new transposition systems of coil strand.