| At present,with the increase of electricity consumption and the widespread integration of distributed generation into distribution network,the fluctuation of power flow in distribution network is enhanced,and the transmission capacity of distribution network is facing challenges.How to make full use of the existing transmission capacity of distribution network and improve the utilization efficiency of transmission components has become the focus of attention of power workers.As an important carrier of power transmission,power cable has the advantages of high reliability of distribution,laying underground,little environmental impact and not easy to damage.It has been widely used in the construction of urban distribution network.Because the transmission distance of the distribution network is shorter than that of the transmission network,and the transmission capacity of the cable line is mainly determined by the thermal limitation,so exploring the thermal load potential of the cable line is the main way to improve the transmission efficiency of the urban distribution network.The essence of thermal load capacity limitation of transmission elements in power grid is to ensure the operation of transmission elements at allowable temperature.Because of the existence of thermal inertia of cable lines,the maximum allowable current of cable can not accurately represent its essential load capacity,which makes the traditional operation analysis and control decision results of distribution network with thermal current as cable load capacity constraints conservative in some cases.In this paper,the thermal characteristics of cables are embedded in the power flow calculation of distribution network to help power system operators fully tap the potential of cable load.The main contents of this paper are as follows:Firstly,the thermal circuit model and parameter calculation method of typical XLPE insulated single-core and three-core cables used in distribution network are investigated;the calculation formula of three-phase electrical parameters of three-phase cables under specific arrangement is derived by Carson formula and Kron simplification method.Secondly,the heat circuit model of XLPE insulated cables is solved and embedded in the three-phase power flow calculation of forward and backward substitution distribution network.Considering the temperature effect of conductor resistance,a three-phase power flow calculation method of procedural distribution network considering the thermal characteristics of cables is proposed.The method is easy to expand under the traditional forward and backward substitution scheme.It can deduce the dynamic change process of the cable temperature in any scenario,realize the prediction of the cable temperature in each layer,and effectively reveal the cable load potential.Finally,In order to minimize the total loss cost in a certain period of time,considering the operation constraints of distributed power supply and energy storage in active distribution network,the equation constraints of single-core cable thermal balance equation and the maximum allowable temperature constraints of cable conductor are introduced to construct the optimal power flow model of distribution network considering the thermal characteristics of cable.The model can make decisions on reactive power output and charging and discharging plans of energy storage devices under the premise that the cable temperature is not exceeding the limit,so as to help dispatch make full use of cable load potential and improve the economic operation level of distribution network.This paper focuses on the two basic issues of power flow and optimal power flow in distribution network,which take into account the thermal characteristics of cables.The research results can be used in the operation analysis and control decision-making of distribution network,help operators to predict and tap the potential of cable load,and hopefully bring considerable social and economic benefits in the efficient utilization of equipment,the safe and economic operation of distribution network and the acceptance level of new energy sources. |
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