Large 3600 r/min induction motors operating below their first system resonant speed

This paper describes experiences with, and design refinements for, large “stiff-rotor” two-pole induction motors rated up to 6050 hp. Comparisons of the “stiff” and “flexible” designs are included. Factory test and in-service vibration data are summarized and compared for one representative motor. The stiff-rotor design´s advantages are summarized for special-purpose or adjustable-speed service at speeds of 3600 r/min and below. An appendix lists recommended mechanical tests for large two-pole induction motors