Study On Heat Capacity Of Transmission Lines Being Operated

On how to increase the transmission capacity, people have commonly focused on the research of the operation and dispatch styles of the power grids, building new transmission lines (also named conductor for short) or improving the ma(?)erial and structure of the conductors. All these actions are basal and important for the increase of the transmission capacity. However, as the key factor of the conductor carrying capacity, the current ratings are always expressed and solved in the conservative way. Therefore, it's significant and meaningful to explore the conductor heat capacity renewedly and ascertain the real-time current capacity for excavating potential transmission capacity.Firstly, based on the review of many domestic and abroad papers, this paper discusses the influencing factors of conductor heat capacity and its mechanism of action. Two representative calculation methods of current capacity is compared and the expressions of current heating, solar heating, convection and radiative cooling are analyzed under operating circumstance, then emulation and heat balance calculation is carried out.Next, according to the different characteristic between conductor temperature and current, the necessity of conductor temperature monitoring and forecast under operating circumstance is discussed. A fast calculation method is presented to trace the tendency of conductor temperature after a disturbance (alteration of current or circumstance conditions) and relationship among power flow, conductor current and temperature is analyzed through the model of electro-thermal coordination power flow which involves the conductor resistance calculation as connecting link and the heat balance equation for the temperature expression as a core. All that above not only provide a basis for the estimate of the conductor heat capacity of operating circumstance, but also present the analysis and calculation methods for the definition and utilization of real-time carrying capacity.Finally, based on the relationship between current and temperature of transmission lines, the problems being studied by predecessors are concluded and summarized, the concept of static thermal rating and transient thermal rating are defined. Then, a concept of advance thermal rating with the consideration of physics rules, conductor temperature and permitting time for temperature rise is proposed from the view of operation dispatch and control and its application occasions are performed according to the thermal inertia. The concept and definition of thermal rating has been developed.Above all, transmission capacity is limited by the utilization of current rating, advance thermal rating of real-time circumstances can exert the potential transmission capacity, further enhance the ability to withstand contingency and bring more social benefit.