Study On Field-Circuit Coupled Modeling And Application Of Impulse Current In Ground

Thunderstorm disasters occur frequently in the Pearl River Delta.Lightning strikes on transmission poles and towers cause huge lightning currents to flow into the ground through grounding devices,seriously affecting the surrounding environmental safety.For example,after thunderstorms,fish died in fishponds in the Pearl River Delta region,causing huge losses and security threats to local residents.The magnitude of lightning current is large,which contains abundant high frequency components.Inductance effect and spark effect will occur in grounding device and surrounding soil under the action of lightning current.These two phenomena make grounding device show complex impact characteristics and affect the process of current dispersion in the ground.The sand pool experimental platform of grounding device is built,and the spark effect of grounding body can be effectively analyzed by comparing the impact experimental data of different topological forms with the impact divergence model.The impact dispersion characteristics of horizontal grounding,cross grounding and grounding with short conductor considering spark effect are obtained by simulating different topological grounding bodies.Combining circuit theory and electromagnetic field theory,the field-circuit coupling finite element model of transmission tower grounding device is proposed,and the finite element software COMSOL Multiphysics is used to build the model.The model is used to calculate the impedance angle,impedance value,leakage current distribution and ground potential rise waveform of grounding body at different frequencies.Compared with the results of CDEGS,the error is less than 9%.The time delay effect of grounding body is also analyzed.The model is proved to be effective in analyzing the inductance effect of grounding device.Combining with the established impulse current model,a field-circuit coupling model considering both inductance effect and spark effect is established,and a small grounding body impact sand tank experiment with additional inductance is designed to verify the comprehensive model.The error is less than 5%.Therefore,through comprehensive analysis,it can be concluded that the proposed field-circuit coupling model is effective in analyzing the inductance effect and spark effect of grounding devices.An experimental platform was set up to study the resistance of fish body under impulse current.The conductivity of adult grass carp was 720?s/cm-1100?s/cm.The response of irreversible damage to internal tissues of fish was observed by long-term follow-up.The threshold of electric energy density in fish was obtained by finite element model,which was 4699mW/cm~3.Based on the above data,the disaster situation of the water around the tower was studied.When the fish pond existed on one side of the tower and was near,about 4.8%of the fish in the pond would be unbalanced.The unbalanced water area was about 135.2 m~2,and there was almost no area of direct death.When there are fish ponds on both sides of the tower,the affected area is about twice as large as when there are fish ponds on one side.When the fish pond is 6m away from the lightning tower,the disaster area of the fish pond is almost zero.