Evaluation Of Voltage Sag And Research On Suppression Measures Based On Vulnerable Area

Voltage sags can cause the failure of sensitive equipment and the interruption of product ion lines,and bring unpredictable economic losses to enterprises.The voltage sag vulnerable area can direct ly reflect the voltage sag problem caused by the line faults.The analysis of vulnerable area is the premise of comprehensive evaluation of the voltage sag.The evaluation of voltage sag is the index to measure the high-quality and reliable power supply capacity of the system,and is the basis for improving the design of the power grid.Weighing the loss obtained from the evaluation of voltage sag and the investment cost of suppression measures,a reasonable voltage sag suppression scheme can be obtained to reduce the adverse effects of voltage sag on sensitive equipment.In order t o quickly and accurately identify the vulnerable area,a fast calculat ion method of the vulnerable area based on the charact erist ics of the voltage curves of sensitive nodes is proposed.Taking the single-phase ground fault of the line as an example,this paper analyzes the voltage expression of the sensitive node and def ines the consistency parameter and the monotonicity parameter composed of the element s of the node impedance mat rix.These paramet ers are used to determine whether the volt age curve is monotonous.On this basis,the lines are divided into two categories to use different methods to calculate the crit ical fault points.The results of the case analysis show that,compared w ith the exist ing analysis method of vulnerable area that ignores the charact eristics of the voltage curves,the algorithm improves the calculat ion speed under the premise of ensuring the accuracy.The algorithm also provides a basis for calculating the dist ribut ion of node voltage magnitude during the subsequent evaluation of voltage sag.Existing methods for evaluat ing t he impact of line f aults on sensit ive nodes are insufficient.Considering the impact of the magnitude and durat ion of voltage sags on sensitive equipment and the difference in voltage tolerance of sensitive equipment,this paper proposes a method to evaluat e the economic loss of sensit ive equipment caused by line faults.First,the magnitude and duration are divided into multiple intervals.Then,the probability that the magnitude and duration of the node voltage sag are in each interval is calculated when the line fails and defined as the occurrence probability of voltage sag occurrence.Finally,combined with the occurrence probability of voltage sag and the failure probability of sensitive equipment in each interval,the failure probability of sensit ive equipment and the total economic loss caused by the line faults are calculated.This method can lay a solid foundation for the subsequent work of formulating voltage sag suppression measures based on economic loss.Taking into account the changes of various parameters of the line after the overhead line is modif ied into a cable,this paper proposes a method to study the planning of the transmission line modificat ion.First,the optimization model of the planning of the line modif ication is established,taking into account the modif ication benef its and modificat ion cost s of each line.Then,w ith the goal of maximizing economic benef its,the cuckoo algorithm is used to solve the model to obtain the specif ic lines that needs to be modif ied.In the case analysis,considering that the power supply company may have limited investment in line modif ication each year,the calculat ion process is d ivided into one-time modificat ion and phased modif ication to find the opt imal line modificat ion schemes respect ively.This method can plan the lines to be mod ified in detail,and provide a basis for the syst em side to suppress voltage sags.