Analysis Of Lightning Overvoltage On Distribution Line And Arrester Protection Characteristics

The insulation level of distribution lines is generally low,the lightning effect poses a great threat to them.Overhead lines are often laid in the form of transmission cables before entering the home,lightning electromagnetic waves can easily invade the terminal equipment through the coupling of transmission cables.Due to the limited line corridor,10 kV distribution lines and transmission lines will be erected in parallel,and its lightning protection characteristics are very susceptible to parallel transmission lines,so it is necessary to analyze the characteristics of the lightning electromagnetic wave coupled with the overhead conductor and the impact on the distribution line after the lightning strike of the transmission line.In order to improve the lightning protection efficiency of the lightning arrester,it is necessary to analyze the impact of the lightning transient characteristics on the line terminal equipment.Firstly,an integrated model of overhead cable and lightning channel is established,the simulation of 8/20?s single-pulse and multi-pulse lightning current is used to analyze the cablecoupled lightning overvoltage waveform and energy characteristics.Shielding effect of transmission lines and interference of transmission line under lightning on distribution line were analyzed.Coupled electrical circuits of distribution lines and transmission lines were also established in EMTP to calculate induced overvoltage on the distribution line,and the influencing factors are analyzed.Set up a complete distribution system model of the transformer on the installation pole,and analyze the comprehensive impact of different factors on the transient characteristics of the terminal equipment.Finally,the multi-attribute decision-making method is used to calculate the weight of each factor that affects the lightning protection level of the lightning arrester installed on the distribution line.The results show that:(1)the coupling voltage waveform of the overhead cable is attenuated in the form of damped oscillation,the overall amplitude of the coupling voltage increases with the increase of the impulse current,under the multi-pulse conditions,the two are not corresponding to the proportional relationship.Under the impact of single-pulse,the coupled energy increases exponentially with the peak value of the impulse current.Under the impact of multi-pulse,the total energy of the coupling increases with the increase of the peak value of the impulse current,but when the coupling voltage is overlapped and interconnected,it will couple a large amount of energy within a few microseconds,resulting in the phenomenon of low lightning current but with high energy.(2)The height of the shielding line of the transmission line has a great influence on the shielding coefficient.When the height of the shielding line is 30 m and 15 m at 15 m spacing,the shielding coefficients are 0.996 and 0.409 respectively.Induced overvoltage on the distribution line decreases as the increment of height of the shielding line,it decreases with the increase of the horizontal distance and height difference between the two,and increases with the increase of the grounding resistance of the transmission line.When the shielding line height is increased from 10 m to 20 m,the line induced overvoltage is reduced by 17.0% and when the horizontal interval between the two increases from 20 m to 30 m,it is reduced by 18.5%.In case of poor grounding,the line induced overvoltage is very easy to exceed its insulation level.(3)The overvoltage on terminal equipment increases with the increase of the grounding resistance of arresters.Damage probability on it increases with the increase of it.When the grounding resistance of arresters is 4 ? and 30 ?,the damage probability values are 8% and 32% respectively.After the shielding line is layed and the shorter the interval between poles with arresters,the smaller the overvoltage of terminal equipment.when the grounding resistance of the arrester is 8? and without shielding line,the spacing is reduced from 180 m to 60 m,the terminal overvoltage amplitude is reduced by 29%.So through the installation of arresters and reducing the interval between poles with arresters,the lightning protection level can be maintained,but the grounding resistance of arresters in high resistivity areas can be improved.(4)In the case of not installing lightning arrester,the weights of the four impact factors of the lightning protection line,the tower grounding resistance,the improvement of the line insulation level and the installation of the lightning protection clearance are: 0.123,0.3098,0.081,0.0617,It shows that the tower grounding resistance has the greatest influence on the lightning resistance level of the line.After installing one,two,and three arresters,the weights of each factor are: 0.0839,0.1781,0.059,0.0731,0.123,0.1844,0.2985,The proportion of lightning arresters installed is much larger than other factors.After optimizing the installation method of the arrester,the total number of lightning arresters installed was reduced from 6 to 5 before optimization,and the lightning strike rate of the line was reduced from 2.386 times/100 km.a to 2.012 times/100 km.a,it can improve the utilization rate of the arrester effectively.