Clarifications on the integration path of transient energy function

In transient stability analysis, a nonintegrable term is present in the energy function of multimachine power system with transfer conductance. There are two approximation methods, linear path method and trapezoidal approximation method, in calculating the energy numerically. It is proved that there is a special point in the orbit of a point in the stability region, where angular coordinates are equal to, or infinitely close to, those of the stable equilibrium point. Integration path for a point in the stability region is the trajectory from the special point to it. Present assumption on the starting point of the integration path is modified. Linear path method takes a linear approximation of the correct path, while trapezoidal approximation calculates along the fault-on trajectory, which is different from the correct path. Thus the latter method is not preferable in calculation.