Annular Gap Windage Loss Measurements for High Speed Electrical Machinery

Windage loss in small, high speed electrical machinery is often predicted using fairly simple quasi-empirical correlations. Many of the correlations used are primarily based on testing performed with larger test articles, at lower speeds, and often with liquid lubricants. This paper presents a new set of air gap windage loss test data for test articles that are more nearly representative of small, high speed electrical machinery. These data were obtained using a unique new test rig. This rig was designed around test articles that are representative of 50 to 200 kW machinery operating up to 60 krpm with air as the fluid in the rotor-stator clearance. This paper describes the new test facility and presents data for a smooth surface 72.4 mm rotor with both a smooth stator and a stator with simulated winding slots, for a range of clearances. The smooth surface results are shown to be in reasonable agreement with previously published results for annular gap windage power loss.