Research On Transmission Capacity Improvement Considering Transmission Section Short-time Overloading

By reason of the economic development and uneven distribution of energy resources,making China’s inter-regional transmission quantity across provinces and provinces increasing year by year,a higher capacity of the power transmission of the cross-section is in demand.There is no doubt that strengthening transmission channel construction is the basic measure to ensure the transmission capacity.However,on the one hand,with the cost of land acquisition and environmental constraints,opening up new transmission corridors,and even new lines become increasingly difficult.On the other hand,regional power shortage and electricity surplus are often alternating,thus blind expansion of the line is not superior decision-making.Therefore,on the basis of the existing transmission equipment,with the full use of economic development volatility the potential transmission capacity can be excavated.By using the time difference between the load and the ambient temperature and the lag effect of the conductor temperature,the section transmission capacity can be enhanced by allowing the short-time overload of the section,and consequently the economical efficiency of the system can be improved under the premise of ensuring the safety of the system.With the power grid structure strengthening and the interconnection of the regional power grids more close,the thermal stability limit in the system security plays an increasingly important role.However,the traditional thermal stability limit is determined by the maximum allowable current of the current-carrying conductor and does not accurately reflect the safety state of the section.In fact,the load change caused by the cross-section overload is often only continued for a short time.During this time,the temperature of the section line can still be maintained within the maximum allowable temperature without load shedding.Hence,it can not only avoid unnecessary load loss,but also avoid the cascading reaction of successively overload tripping caused by line cut-off and redistribution of power flow in a short period of time to increase cross-section transmission capacity.Based on this idea,with the basic theory of dynamic line rating and the transient heat balance equation,the paper propose a overloading method to improve the transmission capacity on account of the daily load curve and the air temperature prediction curve.First of all,based on the thermal stability balance equation of the wire,the paper carries out the transient simulation of the conductor temperature by MATLAB software,and analyzes the influence of different environmental factors on the wire temperature.Secondly,the lag effect of the conductor temperature is analyzed.With the load curve and temperature prediction curve,the temperature of the conductor is calculated.The model is linearized by the decomposition and fusion of the load curve,which simplifies the solution of the modeling process.Finally,a model of the cross section load flow and the conductor temperature is established.The BS23 algorithm and the steps of the model put forward.The model can be used to calculate the cross-section conductor temperature dynamically and determine the short-term overload capacity of the section to improve the transmission capacity.By way of the simulation of a 16-node system,it shows that the method proposed in this paper can retain the peak load and keep the line temperature within the allowable range.Therefore,the transmission capability of the section can be improved effectively under the condition of ensuring the safety of the system.