Abstract
An unusual case of torsional oscillation was observed recently on several large induction-motor drives used for tunnel ventilation on the Pennsylvania Turnpike. These drives, which consist essentially of an induction motor driving a heavy centrifugal fan through a speed reducer, showed a severe torsional oscillation (with a double amplitude around 80 deg) at a point between two thirds and full speed during the accelerating period. These vibrations were found to be self-excited, as a consequence of the negative damping inherent in the shape of the speedtorque curve of the normal induction motor.
After consideration of various methods for eliminating the trouble, a torsional-vibration damper of relatively simple design was developed. Torsiograph records made on the actual drive showed that the oscillation was reduced to negligible values by the use of this damper.
Since induction-motor drives of this general type are used rather widely, it was felt that an account of this investigation, including the methods of calculating damper capacity, the laboratory tests on the damper, and the field tests on the actual drives would be of value to engineers, particularly those interested in vibration.
Discussion: “Investigation of Self-Excited Torsional Oscillations and Vibration Damper for Induction-Motor Drives” (Wahl, A. M., and Fischer, E. G., 1942, ASME J. Appl. Mech., 9, pp. A175–A183)
