Estimation Of Overhead Transmission Line Heat Capacity And AC/DC Power Flow Calculation Considering Electro-Thermal Coupling

Compared to the construction of power generation and load, the expansion of transmission corridor always doesn’t adapt with it. Transmission line load ability can easily become obstacles of power generation and load development. The role of reactive power compensation is to relief the operation condition limits, then drive the line load ability to the heat capacity under temperature limit. Under this background, how to dig the potential transmission line heat capacity based on the current power grid has become a subject that need to be researched urgently.The maximum allowable current is used to judge line heat capacity in project application, which is formulated taking no account of variable weather and thermal inertia. Its shortcoming of conservative and single provides theoretical possibility for digging potential line heat capacity.Started with the heat balance equation, this paper researches the electro-thermal coupling characteristics of transmission lines, reverts the limit of transmission line heat capacity from line current to temperature essence, then analyzes and discusses the line heat capacity from two aspects:single transmission component and power system. The detailed work can be described as follows:First, based on the mechanism of heat gain and loss of transmission lines, the four impact factors of transmission line heat balance are elaborated and analyzed; then the physical means of heat balance equations are described. On the basis of static heat balance equation, the transient heat balance equation is simplified to express transient parameters such as temperature and transient temperature rise time in analytical ways. The weather parameters which influence on the heat balance of transmission lines are discussed in the form of case study, and the assessment results of the static and transient line heat capacity show what the role they play in the dispatch.Next, with the analytical law between temperature and resistance of transmission lines as the core, the method of tracking and predicting transmission line temperature is researched. Some simulation analysis of transmission line temperature and corresponding resistance under operating condition is made to explore the real time varying process of temperature and resistance amplitude distribution in the frequency spectrum. In the case that the accuracy of low-pass filtering method used to filter the calculated resistance from SCADA information directly can’t meet the requirement, a dynamic estimation model of transmission line temperature including resistance is established with Kalman filtering method. SCADA information redundancy is utilized to improve the estimation precision and the idea of temperature estimation without other monitoring equipment being required is realized, which is expected to provide temperature reference for system monitor.Final, combined the AC/DC power flow with the electro-thermal coupling power flow, a model and algorithm of AC/DC power flow considering electro-thermal coupling laws are provided. Based on the characteristic of current being expressed explicitly in heat balance equation, a AC/DC power flow model which is fit for the inclusion of transmission lines’ electro-thermal coupling relation is found. Then a correlation model between differencing heat balance equation and AC/DC power flow in which temperature is considered as a state variable is founded. According to the characteristic of the model parameters, the modified equation established by Newton Method is decoupled and simplified. Thereby, temperature and power flow can be resolved by alternative iteration method, which can improve the applicability of the algorithm used to solve this process power flow problem. This model and algorithm lay foundation for the research about electro-thermal coordination theory under the pattern of AC/DC power grid.In conclusion, it’s significant and meaningful to research lines’electro-thermal coupling laws and apply it to system level for improving the utilization rate of transmission lines and ensuring safe and economical power grid operation.