Research On Status Assessment And Three-phase Capacity Planning Methods For Low-voltage Reactive Power Compensators

Low-voltage distribution has characteristics of huge number of nodes, radial structures and three-phase asymmetric. It’s running condition is critical to the power quality of customers. Low-voltage reactive power compensators are the most important compensating components in low-voltage distribution, which are widely distributed. Unreasonable capacity planning or control, which leads to bad compensation effect is one important reason of undervoltage/ highvoltage phenomenon. Assume that the status of compensators can be monitored and assessed, the problems will be identified and the issues will be solved. At present, the capacity of compensators is planned as 20~40 percent capacity of transformers, which is based on the existing guidelines and engineering experience. However, the actual load of transformers is diversification. There are lots of transformers in light load. Therefore, with the consideration of the characteristics of load change, three-phase asymmetry and the capacity fade of the capacitors, this essay has a research on status assessment and three-phase capacity planning methods for low-voltage reactive power compensators. The main contents are as follows:An index system is proposed in this paper to assessment the operation status of low-voltage reactive power compensators. With the consideration of direct balancing principle, operation characteristics and the traditional standards of power quality, the reason of disqualified moment, symmetry of three-phase load power and operation of compensators are also considered into this index system. The software which is developed based on the presented index system, has been applied in an actual power system. The simulation results of 13 compensators verify that the model is necessary and effective.The three-phase power flow model for medium and low-voltage distribution is presented. Based on the traditional model, the line-phase transformation model of Dyn11 transformer and the modified line model are both introduced in this new power flow model. The forward-backward sweep method is applied to solve this model. The simulation results of a virtual test system verify that this model is more effective and accurate than the old one.The three-phase capacity planning model for low-voltage reactive power compensators considering the characteristics of load change, three-phase asymmetry and the capacity fade of the capacitors is presented. Based on the load samples collected from substations and the results of mid term load forecasting, the planning model takes the maximum recoverable rate of investment as the optimization target. Compared with the traditional planning model, this model increases constraints of three-phase voltage amplitude, three-phase compensation capacity, allocating capacity and grouping capacitors. The immune genetic algorithm is applied to solve this model. The simulation results of 13 compensators demonstrates the effectiveness and practicality of this model.To sum up, in this paper, status assessment and three-phase capacity planning methods for low-voltage reactive power compensators considering the characteristics of load change, three-phase asymmetry and the capacity fade of the capacitors are presented. The results of assessment and planning provide the decision-making basis to solve the problems of capacity planning, optimizing operation and controlling for the low-voltage reactive power compensators.