Investigation into damping-torque coefficients and stability of a 2-synchronous-machine system employed in synchronous starting

The region of minimum damping for a 2-machine system, which occurs at low speeds, in which self-excited hunting may take place is investigated. Under certain circumstances, it is shown that, even where machines are provided with satisfactory damper windings, negative-damping phenomena may be exhibited. A transfer function for a 2-machine system is set up to which various stability criteria may be applied. Frequency-response curves for a typical system which may be employed in a large pumped-storage scheme are given. The rotor oscillations obtained by tests on an actual system are reproduced, and comparisons are made with predictions obtained by application of the stability-criteria method which is developed.