The direct method of Lyapunov is used to estimate the stability region of power systems. A method for the construction of the Lyapunov function, which has been developed recently, is applied to a single-machine system with and without a velocity governor. Such method is based on a construction technique of the Lagrange's state function resulting from second-order ordinary differential equations. The stability region given by the obtained Lyapunov function is compared with those given by other Lyapunov functions and is found to be useful in the power system transient stability problem. Furthermore, its construction procedure seems to be concise. 紀要論文