Error assessment in inadequately represented power-system networks

In power-system load-flow and stability studies, transmission lines are usually represented in various forms which are not exact. Although errors in representation are apparently insignificant, it is shown that they can have a cumulative effect on the outputs of various synchronous machines in the power system. A method is presented, utilising the principle of moments, which enables the overall error in active-and reactive-power outputs of synchronous machines to be obtained with the help of a load-flow study under steady-state conditions. The method works equally well for active power and reactive power separately, as well as in complex form. Numerical examples are included to indicate the possible seriousness of such apparently small errors, and the desirability of including the effects is discussed, particularly in studies which employ a high degree of refinement.