**AUTHORS:**Yi Tao, Wang Yanjie

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**ABSTRACT:**
The network equations of electric power system are formed in which the node voltages and branch currents are as state variables by equivalent circuit simulation of power components. The explicit expressions of power system voltage equilibrium solution curves are obtained by solving the equations above, and then get the characteristic equation of the saddle-node bifurcation point, define the full-dimensional saddle-node bifurcation point. The full-dimensional saddle-node bifurcation point is the closest stability margin of the system after comparing the one-dimensional and full-dimensional saddle-node bifurcation point. In order to solve the system stability margin the dimensionality reduction algorithm of saddle-node bifurcation point is proposed. IEEE-14 nodes system simulation shows that the concepts and methods presented in this paper are correct.

**KEYWORDS:**
Full-dimensional, branch current, saddle-node bifurcation point, power flow equation, equilibrium solution curve, Stability Margin

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