Reliability Research Of Distribution System Considering The Voltage Sags And Short Interruptions

With economic development, high-tech equipments are applicated widely, which are sensitive to voltage changes. Voltage dips or short-term interruptions often result in these devices working incorrectly, or even malfunction. Voltage sags and short interruptions have increasingly become the most important dynamic power quality problems. The impact of voltage dips should be taken into account when analyzing the reliability of distribution system where including Sensitive load to establish scientific and reasonable reliability evaluation system of distribution system which can reflecting the mutual interest of the supply and customers.First of all, the paper introduced the basic concepts of voltage sags and the necessity to establish the evaluation system of sags, analyze and compare the existing various sags evaluation indices at home and abroad, which are the theoretical basis of evaluation; Assessing voltage sags characteristics is the first step, the second chapter establish a complete algorithms of simulation and analysis, and take the standard test system with six buses for example in order to acquire available data.Secondly, the research about the equipments'sensitivity to voltage sags is essential for assessing the impact of voltage sag on the user and system reliability. This paper discusses the uncertainty of the involved in the sensitivity of equipments, and suggests a probabilistic model for the sensitivity estimation based on the cumulative distribution function, quantifying sensitive loads trips due to voltage sags. Then, the analysis and comparison show that the method is reasonable and practical.To reflect the impact on the users and the traditional reliability of power caused by voltage sags, the following assessment methods and indices are proposed:1) Determine the most serious sensitive areas of the user by analyzing the sensitivity of the device and sensitive load; then, the number of expected sag events index (AENSS and AENSC) is proposed, which reflecting the times of sag-event suffered by customers over a specified time period.2) An assessment method is presented based on estimated probability is proposed based on the probability of equipment outage:the effect of sags and short interruptions on customers is quantifying as the number of load trips (SAEIFI-Sag and CAEIFI-Sag).3) Considering the restarting time and the load trips probability, the time of power supply unavailable due to voltage sag is counted into the calculation reliability rate index.Finally, the power reliability assessment system considering voltage sags is set up on the basis of the previous chapters. The proposed methods are verified reasonable and exercisable by the analysis and calculation the standard test system. Some effective measures to alleviate effects of voltage sags are introduced briefly in the end of the paper.