Variable Parameter Equivalent Model for the Loadability of Key Transmission Line

In order to obtain the loadability of key transmission line under operation, a variable parameter equivalent model of power systems is proposed. This equivalent model was first inferred theoretically. And then, a practical method was given for forecasting equivalent parameters. At last, the feasibility and effectiveness of the equivalent model and the method were testified by a 9-node, 12-branch, and 5-machine test system. Empirical results show that the equation model can reflect the effect of parallel flow on the transmission line loadability in interconnected system. And the changes in the equivalent parameters can reflect the nonlinearity and time-varying properties of power systems. The model and method are feasible and effective in obtaining the loadability of transmission line.