Torsional interaction between nonidentical turbine generators

Abstract

Torsional interaction between non-identical generating units with a coincident torsional mode is investigated. The generators are electrically identical but have differences in their mechanical parameters. The mechanical system of each generator in the two-machine model is represented by. the modal model; this enables independent variation of mode damping, inertia and frequency which is not possible to achieve with the conventional spring-mass representation.The studies show that in a system without series capacitance, differences in mode damping affect the phase deviatioa but not the relative amplitude of torsional oscillations; the opposite being true for mode inertia and frequency differences. The amplitude and phase characteristics are both greatly affected by series capacitance for a difference in any mechanical parameter.

Research on Shaft Subsynchronous Oscillation Characteristics of Parallel Generators and SSDC Application in Mitigating SSO of Multi-Generators

“…In reference [11], it is shown that the phase relationship and relative amplitude of the generator masses in common-mode and anti-mode are also very dependent on the presence of series capacitors, especially when the electrical natural frequency matches the mechanical one. This is because under this condition, the magnitude of the electrical damping coefficient may become very large and have a noticeable impact on the oscillation modes of the system.…”

“…For non-identical generators, equivalence is barely possible. Reference [11] investigates the torsional interaction of two non-identical generators with a common mechanical natural frequency, revealing that there will be noticeable phase difference of speed deviations of the two non-identical generators under their common mechanical natural frequency when oscillation occurs. This paper further investigates such situation, showing that if the equivalent electrical stiffness coefficients of the system are much smaller than the modal stiffness coefficients of the generator shafts, then in the anti-mode, the generator masses of the two shafts will oscillate almost out-of-phase, and the oscillation amplitudes of the generators masses are nearly reversely in proportion to the corresponding modal inertias.…”

Application of STATCOM for Damping Subsynchronous Resonance in a Multi-machine System

“…For systems that have parallel identical turbine-generators or non-identical units having torsional modes of the same frequency, generators may suffer from the same mode of torsional interaction at a certain series compensation degrees. Reference [2,3] conducted a research on the SSR characteristics of two kinds of multi-machine system. Results show that oscillation behaviors of unequally-loaded parallel identical generators and non-identical units having torsional modes of the same frequency may have different amplitude and phase, relating to their output level or modal parameter differences.…”