DETERMINATION AND ANALYSIS OF LOAD FLOW CASES FOR TRANSMISSION SYSTEM PLANNING

摘要

This paper presents a method to determine a minimum number of representative, realistic load cases, which cover all critical power line loading situations in a certain period. The load flow in meshed transmission grids is caused by the distribution of load and generation and depends on the grid structure. Extensive wind generation in combination with operation of pump storage power plants and extensive electrical energy trading introduce additional challenges to network planning. Thus conventional load cases - e.g. peak load - are not always adequate to cover all critical power line loading situations in grids.With the herein presented method it is possible to determine a set of load flow cases (SLFC) considering the occurrence probability of critical situations. The number of required load flow cases within the SLFC depends on1. the grid size,2. the grid topology3. the observation period,4. the defined accuracy defining the critical loading and5. the duration of critical loading situations.We investigated the impact of these criteria on the number of load flow cases and on the SLFC's information content and we defined the boundary conditions for the proposed planning tool. The basic input data for this method are the measured active and reactive line loading data from SCADA in meshed transmission networks and the maximum transfer capacities of the elements (e.g. overhead lines, cables and transformers). Besides the theoretical background the paper provides results from the application of this method in real world transmission networks. Those resulting sets of load flow cases are furthermore analysed with respect to the significance and the relevance to actual line loadings.The proposed approach to determining a set of load flow cases can be used for power system planning with regard to 1) increasing demand, 2) new power plants, 3) new substations which affects the grid structure and 4) repowering of existing lines. This derived set of load flow cases gives a comprehensive and representative overview of the expected situation and provides the basis for power system planning tools using multiple scenarios to handle uncertainties.