A Study On The Reactive Power Planning Of Urban Transmission Network

With the increasing electricity demand and the expanding of the power system, network planning is becoming a heavy task. As a major component of network planning, the reasonable reactive power planning can enhance the power system security and reliability, for it can control voltage, reduce energy loss, and save equipment investment and operation cost. Local balance principle is not applicable, because the transmission network is ring type supply and the node voltage is strongly related to reactive power. Therefore the reactive power planning of transmission network is a difficult problem for the grid planners.In this paper, the reactive power planning of urban power transmission network is analyzed in detail. On the basis of this analysis, a new solution strategy is presented. And the examples'result validates feasibility of the method.Firstly, the reactive power planning of urban transmission network is a multi-purpose nonlinear programming problem. According to this problem, a mathematical model is established in this paper. The features of various normal operating modes are taken into account in this model, as well as the entire network reactive power optimization algorithm. In the smallest load operation, the mathematical model has set optimal active power loss as the goal. So a single group's reactive power compensation equipment capacity, which is equipped with the new compensation node can be determined. In the biggest load operation, the mathematical model has set optimal integrated economic efficiency of equipment investment and network operation cost as the goal. So the new compensation node's reactive power compensation equipment group count and capacity in the normal operating mode can be determined. With the help of this model, the problem including the unity of goal and step-by-step determination of equipment is solved properly. And it is beneficial to achieve network optimization economically and securely.Secondly, in the above mathematical model, the particle swarm optimization algorithm is adopted as the method to solve the problem of the whole network reactive power optimization in this paper. And this algorithm is modified in two aspects according to the practical problems. First, the update deficiency of basic PSO in handling discrete variables is modified, so as to adapt to the step regulation of transformer tap and the throw-in of reactive power equipment in group. Second, the possibilities of negative direction flight are introduced in the update equation, so that the particles'ergodic property in the discrete space is increased. I is beneficial to converge to the global optimum value much faster.Finally, through IEEE-14 and a city transmission network which is a 195 bus system, the rationality of the reactive power programming model and the effectiveness of the method are validated.