Study On The Measurement And Assessment Technology Of The Current Dispersal In Earth When Lightning Strike Tower

When the lightning strikes the transmission line tower,the lightning current with the large amplitude flows through the tower grounding device and disperse in the earth,and the current density is very large.When the transmission line approaches the paddy fields and the ponds,due to the difference of electrical conductivity that leads to the local dispersion concentrating and thus causes the problem of biological safety in the pond.For example,there're many incidents of a large number fish deaths in pond near the tower in Guangdong region after thunderstorm,which brings long term security risks for aquatic organisms and local residents.Many power transmission towers ignore the safety problems brought by the dispersive current,there is also a lack of means to measure and evaluate it.Therefore,it is urgent to carry out the study on measurement and safety assessment of dispersive current,and develop a set of equipment to realize the risk assessment of the dispersive current.The fish in the pond is considered as the safety assessment object in the paper.First,a test platform for the fish tolerance impact shock threshold test is built,and the reaction states of the typical fishs under the impact shock are observed.The resistivity of fish based on the equivalent resistance method is measured.The study determine the electrical energy density as the criterion for the fish tolerance impact shock,and then the relation between the electric energy density of fish body and the electrical conductivity of fish with the current density value of fish is derived.Through a large number of experiments and simulation analysis,the electric energy density thresholds of the typical fish under impact shock are studied.Based on the calculated energy density curve of the fish body energy and water energy density,the thresholds value of the impact current density of the fish suitable for engineering practice are given.Secondly,the on-site measurement scheme for the dispersive current flowing from the tower is determined.The finite element model of the grounding device is established,and the influence of the radius of the backflow ring on the dispersion of the dispersive current in the ground is studied,based on which the effective range meeting the engineering test requirements within the ring is given.The study shows the dispersive current test technology in the ground based on the current sensor.Thus it is necessary to design the current sensor and determine its size.Besides the measurable distance of the sensor under a certain amplitude curren is studied,in combination with the effective range of the backflow ring,the test range should be selected in the actual test is also shown in paper.In order to reduce working time and improve work efficiency,the database of fish pond disaster is built and the risk fast-assessment technology of the dispersive current flowing based on database interpolation is also studied.On the basis of those,a set of safety assessment equipment for dispersive current in the field is developed,including the test system which can measure the high frequency current at milli level and the risk assessment software which can realize the rapid assessment of the damage of the fish ponds around the tower.Through the actual test,the test results meet the engineering requirements compared with the simulation,the equipment's function is normal and has passed the inspection of the third party inspection organization.Finally,one tower in Shunde District,Foshan,Guangdong province is selected for the pilot project.Taking a test after the application of long vertical grounding electrode combined with insulated shielding dispersion protection scheme,the results not only show that the scheme has a significant effect,but also show the reliability and practicability of the equipment.