Study On The Time-space Characteristic Of Transmission Bottlenecks And Load Capacities Of Complicatedly Laid Cable Lines

As one of important infrastructure for city operation,cables are widely used in urban power network.Transmission cable lines are usually several kilometers to more than ten kilometers,through the different environmental areas,laying condition of whose becomes much more complicated as the quantity and scale boom.As laying environmental conditions change with the seasons and rainfall,transmission bottleneck that unavoidably exists in the cable lines has the time-space characteristic.Load capacity of cable lines is determined by load capacity of transmission bottlenecks.And cable load capacity which is related to structure parameters of the cable itself,and varies dynamically with the shape of power load and soil environment,has the time-space characteristic too.Therefore,to improve emergency capacity and adapt to economic and social development,it is necessary to study the time-space characteristic of transmission bottlenecks and load capacities of complicatedly laid cable lines.The following issues are researched in this dissertation: steady-state and transient thermal circuits of cable system considering the surrounding medium are analyzed.Based on the heat effect of multi-loops and outer heat sources on cables,steady-state and transient conductor temperature of cables are deduced.Conductor temperature rising tests and an IEC example are carried out to verify the calculation.The model of identifying transmission bottlenecks and evaluating load capacities of cable lines is established.After carding the specific laying and installation conditions of 299 high-voltage cable lines in an area,the summer and winter transmission bottlenecks under continuous load are identified and analyzed statistically.Finally,based on the actual laying environment of typical complicatedly laid cable lines including a 220 kV line and a 110 kV line,transmission bottlenecks under continuous load and emergency load respectively are studied,and the space-time characteristics of transmission bottlenecks,continuous load capacity and emergency load capacity are analyzed.Research about 299 cable lines in a certain area suggests that the proportion of directburied section of transmission bottlenecks in winter is lower than in summer,when the proportion of pipe laying section is higher.General burial depth of transmission bottlenecks in winter are larger than in summer,and the change of load capacities varies from lines to lines.Research about concrete cable lines suggests that different seasons,different emergency times,different initial load currents and emergency load currents affect the segment of the transmission bottleneck.Under the same kind of laying method,the deeper the depth,the lower the emergency load capacity.This study can provide technical support for the monitoring and load dispatching of transmission cable lines and improve the safety of cable operation during peak load periods.