Effect of multiple equilibria on power system stability

This paper illustrates that for the same system loading, a power system may become unstable either due to angle instability or due to voltage instability or due to both depending upon the disturbance. The studies on two sample power systems demonstrate that for certain range of system loading there are many controlling unstable equilibrium points and their unstable manifolds give rise to different kinds of the instability for the same loading. The stability region in parameter space has also been characterized considering saddle-node and Hopf bifurcation to illustrate that the Hopf bifurcation further reduces the stable range of the operating parameters. (C) 2000 Elsevier Science S.A. All rights reserved.