Excitation of Torsional Oscillations in Three-Phase Machines.

It is theoretically and experimentally shown that, when the torsional oscillations are correctly taken into account, completely unexpected conclusions are reached, which explain the problems recently observed and which indicate possible solutions. It is shown that contrary to the previously held opinion, the damper winding is also effective in isolated operation and that the mechanical torsional constant of the coupling components between the driving machine and the generator (when combined with their associated inertia) is sufficient to make the system capable of torsional oscillations even in isolated operation. Formulas are developed which can be used to calculate the electromagnetic damping coefficients.