Analysis on the voltage unbalances due to high-speed railway demands

This paper introduces the analysis of the voltage unbalances caused by the demands of a high-speed railway on a public power system. A powerful three-phase power-flow program with simplified traction substation models is used to evaluate the voltage unbalances in detail. The evaluations consider the interactions between neighboring substations in which large unbalanced traction loads are connected. All of the bus voltages, line currents, system power flows and losses are calculated rigorously. The effects of unbalanced traction loads on a public power system and interactions between neighboring substations are discussed. The simulation results show that the system unbalances are affected by common balanced loads as well as the unbalanced traction loads. The balanced loads amplify the degrees of the voltage unbalances that are caused by the traction loads or other unbalanced loads, such as furnaces. The results also indicate that the degree of voltage unbalances at the point of common coupling is not necessarily the maximum in the entire power system. This fact is of value to consultants and engineers involved in related work and should be emphasized