Network Simplex Method Applied to AC Load-Flow Calculation

Operational research methods, and particularly flow and transportation methods have many applications in the power system field: optimization of hydroelectric power system operation, seasonal or short-time planning of a hydro-thermal system and finally power system security. The purpose of this paper is to specify the network simplex method of the load-flow calculation in a power system. This study is not limited to the DC-flow calculation but particularly presents a model for the full AC load-flow calculation. The proposed model is an imaginary and real current one. It is based on a simplifying assumption which will allow decoupling of the problem and which is the basis of the algorithm called FLF (Flow Load-Flow algorithm). Power system elements such as lines, transformers, generators and voltage control busses are represented with adapted models. Systematic tests have been performed on some existing power systems, such as the IEEE 24-bus Reliability system. The performance of this method is compared with the results of a decoupled Newton-Raphson load-flow. The accuracy of the FLF algorithm is competitive with the Newton-Raphson method, but its speed still has to be improved. However the load-flow calculation is only a part of the power system security problem, where properties and characteristics of flow and transportation algorithms will offer greater perspective.