Intelligent Undervoltage Load Curtailment

Abstract

During major contingencies that impair the reliability of power systems the system operator will take some actions including load curtailment to maintain the voltage level and reliability of the system. The amount of load that needs to be curtailed depends on the required reserve in the system, the load forecast, and the rate of load change in the system. In this paper we apply a Fuzzy Logic method to determine if any load curtailment is required during a contingency. We first categorize all possible first and second order contingencies by the screening algorithm proposed in this paper, which is based on the impact of the contingency on static voltage stability in large power systems. The program then makes a short list of important contingencies for detailed analysis. Contingencies that result in a larger reduction of maximum loadability are placed in Low Contingency Category (or sever contingency), whereas, the contingencies pertaining to smaller reduction are put in High Contingency Category. The contingencies falling in between high and Low categories are termed as Sufficient Contingencies and are placed in third category. The ranking method is tested by the IEEE 118-bus Test System, and then is applied to study a large-scale real power system with 25,000 buses. The program considers the var limit of the synchronous generators and switching scheme for the capacitor banks. At the end of this paper a fast and intelligent algorithm is proposed based on Fuzzy Logic. It can help the operators to make a fast decision about the necessity of load curtailment such that the voltage stability is maintained. The contingencies are assigned with different membership values according to their impact on the system. The proposed Fuzzy Logic algorithm is being implemented to the contingency ranking program and will be published in the near future.