Direct calculation of voltage-stability limit of electric power systems

Abstract

On-line monitoring of voltage-stability conditions is a new requirement for the energy management systems of the electric power industry. Preferred by the utility engineers and dispatchers is an index which represents explicitly the margins to a voltage-stability limit (collapse point) expressed in a physical unit ordinarily used. For example, such indices are the system load and voltage-voltage-stability-margins (SVVSM) between the present operating point and a voltage collapse point. However, long computer time is required to calculate accurately the voltage collapse point by the conventional method because many multiple load-flow solutions are required. This paper presents a new algorithm to calculate directly, exactly, and rapidly the voltage-stability limit. The algorithm uses the load-flow equations and the explicit expressions of the voltage collapse root conditions are expressed as dR/dV = 0, where R is active or reactive power node injection, and modifying the conventional N-R load-flow program, and is not affected numerically by singular Jacobians. The proposed algorithm is verified through calculating the voltage stability limit of a 176-node power system.