Research On Compatibility Indices Between Urban Power Supplies And Sensitive Loads

Sensitive loads are frequently affected by voltage sags,which lead to equipment malfunction.Therefore,the voltage sag compatibility between power supply and sensitive load obtains glare of publicity.The evaluation of the voltage sag compatibility is the base to solve the problem,which includes three aspect: the evaluation of the grid,the evaluation of the loads and the compatibility of each other.According to the evaluation results,consumers can choose reasonable site of factories to reduce the impact of voltage sags from grid side on equipment and choose the equipment with immunity matching voltage sag level of power grid.Consequently,focusing on the compatibility between urban power grid and equipment,this thesis proposes the methods and indices to evaluate the voltage sag level from the grid side,the immunity from load side,and the compatibility indices between each other.The main work is given as follows.(1)According to the distribution characteristics of monitoring data of voltage sag events,the system evaluation based on the average point-to-line distance index is proposed.Cluster analysis is applied to obtain serval intervals on the duration dimension.Then the medians of retained voltage are solved by total events in different intervals.The median line is plotted,which reflects the average voltage sag level of the whole power grid.In order to reflect the sag level of different regions,the point-to-line index is defined as the average of the distance from event points to the median line.On the basis of distribution characteristics of the index values,the rating rules are formulated to classify the voltage sag levels of different regions,which lays the foundation for compatibility index from grid side.(2)According to the polyline characteristics of voltage tolerance curve of equipment,the evaluation method of equipment immunity based on percentile is proposed.Percentiles are specified in each duration interval,and the percentiles of retained voltage are calculated from immunity test data.Then the immunity curves are drawn to classify equipment immunity.After the comparison between voltage tolerance curves and the immunity curves,voltage sag immunity of sensitive load is classified,which lays the foundation for compatibility index from load side.(3)Based on the evaluation of voltage sag level from grid side and equipment sag immunity,two compatibility indices based on compatibility area and gravity model are proposed.The compatibility area is defined as the intersection area,which is below the immunity curves and above the median line.This index reflects the impact of sag level from grid side on equipment.The evaluation results of voltage sag level and immunity classification are defined as the “mass”of grid and equipment respectively.Besides,the quadratic sum of distance between the median line from grid side and the immunity curves from equipment side is defined as the generalized distance between the power grid and equipment.The gravity index is calculated with gravitly model to quantify the matching degree of both sides.The research of voltage sag compatibility can effectively improve the impact of voltage sag on consumers from the planning level,and achieve a harmonious win-win situation between power grid and consumers.