Study On Impulse Characteristics And Test System Of Grounding Devices Of Transmission Line Tower

Grounding devices of the tower for overhead transmission line belongs to the category of lightning protection grounding, which function is to provide access into the earth for lightning current. When dispersing to surrounding soil through the grounding device, the lightning current will raise the potential of grounding device and transmission tower. When the top of the tower potential exceeds a certain value, it will cause the counterattack and flashover of transmission line insulator. Therefore, reasonable designed grounding device of the tower is the foundations to guarantee overhead transmission line operate safely and reliably. It is significance for improving the lightning protection performance of transmission line by reforming some existing ground engineerings. By using simulations, full-scale experiments and simulation experiments, impulse grounding experiment system, concentrated parameters electrical network model and its iterative algorithm, the feature phenomenon of impulse characteristics, the evaluation method of impulse characteristics and distribution of leakage current of square grounding conductors, and reducing resistance measures in high resistivity soil are further studied.1The development of impulse high current experiment system of grounding deviceThe electrical parameter of impulse high current discharge circuit is designed, and put forward a technological scheme including four split style impulse current generators arranged uniformly around circular current-returning electrodes whose diameter is40meters, and successfully realize the aim of impulse current of peak value100kA and waveform8us/20us on the load whose impedance is large than4Ω, and put forward compensation formula and test method based on mutual impedance. Finally, the accuracy and validity of experiment system and experiment method are validated through impulse characteristics test of the T2-4-4stype grounding conductor.2The development and simulation of frequency domain electrical network model considering spark dischargeThe frequency domain electrical network model of tower grounding conductors, considering the self inductance and mutual inductance of grounding conductors and the influence of mutual impedance to the earth between the grounding conductors, is put forward; and the calculation formula of mutual impedance matrix to the earth between the grounding conductors in homogeneous soil model and horizontal two-layer soil model is deduced; and the above validates and algorithm are validated using the software of CDEGS, and the iterative algorithm of frequency domain electrical network model considering spark discharge is put forward. Finally, the above algorithm is validated using full-scale experiments. 3The development of inductive effect and spark effect of single horizontal grounding bodyTaking single horizontal grounding conductor as research object, the impulse characteristics of different length horizontal grounding conductors in different resistivity soil using different wavefront time impulse current as an incentive is calculated and analyzed; and the effect law of capacitor of grounding conductors to the earth, longitudinal inductance, soil spark discharge on impulse characteristics and waveform property of ground potential rise are acquired, and the influence range of various characteristic phenomenon is summarized; and the influence scope of inductive effect and spark effect in impulse characteristics is distinguished.4The simplified evaluation method of impulse characteristics and distribution of leakage current of square grounding conductorsTaking square grounding conductors widely used in tower grounding engineerings in our country as research objects, and the preliminary selection for square grounding conductors in low, medium, and high soil resistivity are performed fistly, and the impulse characteristics of the above square grounding conductors using different wavefront time and different peak value impulse current as an incentive is calculated; and the simplified evaluation method of square grounding conductors impulse characteristics in different resistivity soil is summarized; and leakage current distribution on horizontal ray conductors of square grounding conductors using small scale experiment and simulation is researched; the effect law of impulse current wavefront time, crest value, and soil resistivity on leakage current distribution is analyzed.5Reducing resistance measures of grounding conductors in high resistivity soil and its validity analysisIn view of the existing low resistivity soil layer under the bottom of the earth, the validity of reducing resistance measures of installing vertical grounding conductors is validated. Test results show that the impulse grounding impedance of horizontal grounding conductors and square grounding conductors reduces65%by installing vertical grounding conductors. The120°three-branches structure modification program is put forward, and simulation results of horizontal grounding conductors and square grounding conductors in high resistivity soil area without low resistivity soil at the bottom of the earth is compared between before and after structure modification. The comparing results show that the structure modification can weaken inductive effect, and increase a channel of spark discharge, and acquire reducing resistance effect by some extent.Through the study of this paper, certain results of impulse high current experiment system of grounding device and experiment method, impulse characteristics simulation calculation method of tower grounding bodies, feature phenomenon of impulse characteristics, impulse characteristics of square frame grounding bodies, reducing resistance measures in high resistivity soil are achieved; and some new methods and thinking of impulse characteristics experimental study and simulation are provided, at the same time, impulse characteristics evaluation method and reducing resistance retrofit program for design and reform of tower grounding engineering are supplied.