Study On Electromagnetism Of Extra-High Voltage AC Transmission Line And Sag Monitoring Methods

With the power grid construction speed,the overhead power line voltage rating,the analysis of electromagnetic fields below extra high voltage power line and grid security and stability has become a hot topic at home and abroad.Transmission line sag as an important indicator of circuit design,operation and maintenance,it not only affects the electromagnetic field distribution below power lines,but also affects the security and stable operation of the line.In this paper,make the EHV AC transmission line as research object,calculate the frequency electromagnetic fields under the power line and analyze the three-dimensional distribution.Combine monitoring methods theoretical research and application of EHV transmission line sag,proposed sag monitoring method based on PSO according to electric,magnetic inverse thought.Firstly,based on catenaries' equation,build transmission line physical model suitable for high or not high tower,the three-dimensional frequency electromagnetic field approximate quasi-static field,and use charge simulation method to build the three-dimensional frequency electromagnetic field calculation model with sag.Simulation of the wire arrangement,ground height,phase sequence,line structures and other factors on the size and distribution of the electromagnetic field.The results show that electric field strength below the power lines is mainly determined by the vertical component and magnetic flux density is mainly determined by the vertical component and a horizontal component,and then height and structure of transmission line affect the frequency electric field and frequency magnetic field significantly.Secondly,according to the corona phenomenon establish the three-dimensional electric field of transmission line calculate model with corona discharge.Use particle swarm optimizations calculate corona voltage according to the field inverse thinking.The power line frequency voltage divided from corona voltage and no corona voltage.When the transmission line corona,According to the mechanism of high voltage transmission lines corona discharge divide the analog charge into circuit simulation charge and space simulation charge,calculate separately the electric field intensity generated by two partial charges,and use superposition theorem get the distribution of electric field of transmission lines consider corona discharge.The results show that corona discharge will increase the electric field strength of the transmission line.Finally,based on the measured electric or magnetic fields,to establish the inverse power line sag calculate model,combining PSO to estimate transmission line horizontal stress coefficient to obtained power lines sag.Among them,the use of the measured electric field values to calculate sag required determine whether the transmission line has corona phenomenon to select the appropriate electric field calculation model.By comparing the measured sag values and calculates sag value to prove the effectiveness of the sag monitoring methods.EHV AC transmission line electromagnetic field calculation and analysis has important guiding significance to the transmission line construction.Improvement the wire to ground height,reasonable arrangements for phase sequence and appropriate type of structure can control the electric field strength and the magnetic flux density under AC transmission lines effectively.According to the electric field intensity or magnetic field strength measurements inverse calculate power lines sag,provide power line sag monitoring methods research the new idea.