Estimating The Renewable-Energy Integration Threshold Considering Electro-thermal Coupling Of Overhead Transmission Lines

With the increasing shortage of fossil energy and the deteriorating living environment,the traditional energy supply system is facing severe challenges.Therefore,renewable energy such as wind power and solar energy has developed rapidly with its environmental and economic advantages.With the increasing scale of new energy base,it is of great significance to study the wind power or photovoltaic grid-connected capacity limits accepted by the main power grid for the sustainable and healthy development of new energy generation and power system.In China,due to the obvious imbalance and regional differences in the distribution of wind energy,overhead transmission lines are responsible for the transmission of new energy such as wind energy and solar energy to the main power grid system.Therefore,the power received by the main power system is constrained not only by the generation capacity but also by the transmission limit.The operation of overhead lines is limited by thermal limit.Its essence is that the line temperature can not exceed the allowable value to ensure the safe operation of the system.In addition to the thermal limit,there is a critical condition corresponding to the maximum load point,which can not be tracked only by monitoring a single physical quantity.When this critical limit is reached,the system is unstable.Therefore,the limit is also known as the static stability limit,which is of great significance to system security.Through the study of the electrothermal coupling of overhead wires,the environmental variables are introduced into the power analysis with the correlation of temperature and resistance as the link.The emphasis of this paper is to illustrate the exact relationship between environmental factors and transport limits.Although the nature of thermal limit and static stability limit is different,both of them affect the evaluation value of grid-connected limit of new energy to a certain extent.Therefore,in the actual operation environment,it is urgent to identify the key types of new energy grid-connected restrictions as thermal restrictions or static stability restrictions,and to evaluate and calculate the threshold of new energy grid-connected restrictions limited by overhead lines.Based on this,the main work can be summarized as follows:In the second chapter,the heat balance equation and power equation of the overhead line are given,and the power flow expression of the electrothermal coupling overhead line is given.The environmental variable is introduced into the power limit analysis,and the specific expression formula of the transmission power of the static stability limit is deduced.According to this,the power value at the static stability limit can be regarded as a function of the environmental factor and the transmission distance of the line.A scheme for identifying key restriction types and solving corresponding limit values is presented.Chapter 3 explores the influence of environmental parameters on line limit analysis,reveals the relationship between thermal limit and static stability limit of different line lengths,identifies the key environmental factors that significantly affect power limit value among various environmental factors,and analyses the influence of key environmental factors on wind energy grid connection by combining wind speed correlation between wind farm and overhead line in wind energy grid connection.Case studies are conducted in typical locations of different environments to demonstrate the effectiveness of the method.In the fourth chapter,the influence of solar radiation on transmission capacity of transmission lines under different transmission distances is analyzed,and the relationship between output of photovoltaic power station and solar radiation is analyzed.Considering the heating of solar radiation to the surrounding environment,the influence of environmental temperature and solar radiation on the static stability limit point is analyzed.Furthermore,the key restriction types and photovoltaic access limits under different environments and transmission distances are revealed.