Interaction between subsystems of a power system

The linearized model of a large dynamic system can be broken into subsystems which are easier to compute and understand, and then the interactions of the subsystem eigenvalues when the subsystems are interconnected can be studied. Of particular interest are those cases where the subsystem eigenvalues are all stable while the total system eigenvalues show an instability. A subsynchronous resonance problem is used as an example of this approach. Two machines and the electrical network form three subsystems which are stable. However, the total system is unstable. Using sensitivities or participation factors from the subdivided system, the critical eigenvalues in each subsystem which cause the instability are identified. One interesting result is that the eigenvalues that interact are not the eigenvalues that would have been expected from the classical understanding of this problem.