Research On Lightning Overvoltage Protection Of Oil And Gas Pipelines Near Overhead Power Lines

Electricity overhead lines and oil and gas pipelines are often built adjacent to each other to form integrated energy corridors.When the overhead conductor or tower is struck by lightning,the line adjacent to the oil and gas pipelines overvoltage impact from the line conductive lightning current and tower grounding grid scattering lightning current.At the same time,the insulation layer of oil and gas pipelines will be subjected to high voltage difference due to the lightning current of grounding scattering,which will lead to insulation breakdown in serious cases and cause accidents such as oil and gas leakage.Therefore,it is particularly important to study the impact of lightning strikes on overhead conductors and power towers on the adjacent pipeline overvoltage and overvoltage protection measures.The main research contents include:(1)The lightning current distribution calculation model of 500 kV overhead line-tower is built,and the influence of lightning current amplitude and soil resistivity on the lightning current distribution characteristics under the condition of lightning conductor and lightning tower is calculated respectively.The simulation results show that when the lightning current amplitude is less than the lightning withstands level of line shielding failure,the lightning current mainly exists in the overhead conductor.When the lightning current amplitude is greater than the lightning withstands level of line shielding failure,the scattered flow of the tower grounding grid through the flashover insulator is positively correlated with the lightning current amplitude and negatively correlated with the soil resistivity.When lightning strikes the tower,the lightning current amplitude will hardly change the lightning diversion coefficient.However,the increase of soil resistivity will reduce the diversion coefficient of lightning tower.(2)Based on the distribution characteristics of lightning current when lightning strikes500 kV overhead conductors,the influence of different factors on the over-voltage of parallel pipelines without flashover of line insulators is first calculated.The simulation results show that the induced voltage of the pipeline is the highest when lightning strikes the C-phase conductor.The induced voltage of the pipeline is positively correlated and negatively correlated with the lightning current amplitude and the ’’pipe-line’’ spacing,respectively.The normal operation current of the line has little effect on the induced voltage of the pipeline.Then,the influence of different factors on the overvoltage of the pipeline at the cross crossing under the flashover of the line insulator is calculated.The simulation results show that the induced voltage of pipeline metal layer,the induced voltage of pipeline insulation layer and the withstand voltage of pipeline insulation layer are positively correlated with the lightning current amplitude and soil resistivity,but negatively correlated with the ’’pipe-line’’ spacing.When the ’’pipe-line’’ intersection angle increases,the induced voltage of the pipe metal layer and the pipe insulation layer gradually increases,but the voltage of the pipe insulation layer decreases first and then increases.(3)Based on the distribution characteristics of lightning current when lightning strikes500 kV overhead line towers,the influence of different factors on the overvoltage of oil and gas pipelines at parallel proximity is first calculated.The induced voltage of the pipeline is positively correlated with the soil resistivity,and positively correlated with the lightning current amplitude,but negatively correlated with the ’’pipe-line’’ spacing.The outer diameter of the pipeline has little effect on the induced voltage of the pipeline.Then the influence of different factors on the overvoltage of oil and gas pipelines at the crossing is calculated.The simulation results show that the induced voltage of pipeline metal layer,pipeline insulation layer and the withstand voltage of pipeline insulation layer are positively correlated with the lightning current amplitude,soil resistivity and ’’pipe-line’’ intersection angle.However,it is negatively correlated with the ’’pipe-line’’ spacing.(4)Based on the influence mechanism of grounding current dispersion on pipeline overvoltage near the line,the effectiveness of forced commutation method and solid-state decoupling device to reduce the voltage of pipeline insulation layer is verified.The simulation results show that the protection effect is the best when lightning strikes the tower.The two horizontal forced commutation methods reduce the voltage of the pipeline insulation layer by 7.84 kV and 12.37 kV,respectively.Two vertical commutated grounding grids reduce the voltage of pipeline insulation by 11.81 kV and 12.45 kV,respectively.The solid-state decoupling device can effectively reduce the voltage of the pipeline insulation layer,and the optimal laying length of the bare copper wire is given according to the simulation results.