Research Of Thermal Circuit Model On Overhead Transmission Lines Dynamic Rating

The ampacity of overhead transmission lines is an important parameter in overhead linesdesign and operation. In terms of calculation of ampacity, IEEE738-2006and IEC1597-1995standards are internationally adopted. In China, the Morgan formula is the main method. Theampacity of overhead lines has a closely relation with its operation surrounding, which is astatic rating value calculated under an extremely bad meteorological environment. In spite ofthis, the environment is still favorable for the dynamic lines rating. With the unsynchronizeddevelopment of economy and grid, there are some bottleneck problems in power transmission.Therefore, the concept of overhead lines dynamic rating, deep researches on the feasibilityand means of dynamic rating were proposed by scholars from home and abroad.There are some problems in present overhead transmission lines dynamic rating, forinstance, much monitoring, lower communication reliability and lower accuracy of solarradiation’s quantity. On one hand, due to its high input cost, it is very hard to make it popular.On the other hand, due to its complicated parameters, it has a lower reliability on calculationof ampacity. Hence, on overhead lines, this essay creates a thermal circuit model on dynamiclines rating and the solar radiation heat absorption capacity from sun, builds an experimentalsystem on the basis on heat transfer law. Details are as follows.Firstly, steady-state and transient thermal circuit model on dynamic rating of overheadlines was created on the basis of monitoring the conductor temperature and ambienttemperature respectively. The relationship between allowable current with time is analyzed.The methods of calculating parameters and the means of monitoring temperature wereconfirmed. And an experimental test was made by creating the experimental platform oncompatibilization. According to the investigation, there are fewer monitoring amount and thecalculation error will be within6%without considering the sun radiation.Secondly, this essay creates an analytical model on equivalent thermal resistance on thebasis of heat transfer theory, which are able to comprehensively reflect the following factors’influence on heat dissipation of wire like heat conduction, thermal convection andevaporation and so on. Besides, it builds a simulation methodology on three dimensionalconvection thermal field of overhead lines, which analyzes the following factors’influence onheat dissipation of overhead lines like the temperature difference in lines with environment,wind speed and wind direction. According to the investigation, the air velocity will increaseabout0.2m/s when the conductor temperature rises by40°C. The conductor temperaturedecrease most with the change of wind speed between01m/s.The thermal convection works best at the included angle between60o~70o.Thirdly, this essay firstly adopts the thermal circuit model on sunshine radiation heatabsorption capacity of overhead lines. Monitoring the temperature of virtual lines and runningoverhead lines can realize an accuracy estimate of solar radiation heat absorption capacityCompared with the traditional method, it can better reflect the real situation on theconductor’s heat absorption. This model can comprehensively reflect the relations betweenwind speed, wind direction and environment. According to the experimental data, the relativeerror between4h average data calculated by model and actual value is within4%.Besides, thermal circuit model of dynamic overhead lines rating was created in thisessay. On-line monitoring equipment and system on dynamic overhead lines ratting was built.Moreover, computer used in analyzing the ampacity of overhead lines was invented. Thismodel is able to calculate the dynamic ampacity of overhead line and track the conductortemperature and virtual conductor temperature.