On the Effect of the Machine Saturation on SSR in Power Systems

A bifurcation analysis is performed to investigate the influence of iron saturation on the complex dynamics of a heavily loaded single-machine-infinitebusbar power system modeling the characteristics of the CHOLLA# 4 generator with respect to the SOWARO station. The system has five mechanical and two electrical modes. The results show that as the compensation level increases, the operating condition loses stability via a supercritical Hopf bifurcation. As a result, the power system oscillates subsynchronously with a small limit-cycle attractor. The instability is due to the interaction of the subsynchronous electrical mode with one of the torsional modes. When the machine saturation is considered, again the system loses stability via a supercritical Hopf bifurcation; however, it occurs at a slightly lower level of compensation, indicating that the influence of machine saturation is slightly destabilizing.