Research On Tower Foundation Resistance Reduction Strategy By Wrapping Flexible Planar Electrode Around Tower Foundation

With the rapid development of China’s economy,the need for electric power is increasing,as well as power grid’s voltage level and system capacity.Especially with the development of UHV power transmission engineering,power transmission system needs to be more reliable.Power system operation experience suggests that most transmission line faults are caused by lightning strikes.Reducing grounding resistance of transmission tower is an effective way to lower lightning trip-out rate.For overly-high grounding resistance towers,many resistance reduction methods are effective,but long-distance excavation and large land occupation increase project budget.Meanwhile,galvanized steel has a service life of 8 to 10 years.Metal grounding electrodes face erosion problems.Engineers and researchers seek for substitutes for metal grounding electrodes.Emergence of non-metal graphite flexible electrodes improve the erosion situation.Reducing transmission tower grounding resistance by using anti-erosion grounding materials in limited area becomes an emergent subject.To discuss solutions for the above subject,the main work is as follows:(1)After analyzing domestic and foreign researches on tower resitacne reduction,this paper applies FEM-based multi-physics software packages COMSOL Multiphysics to simplify tower foundation models.The simplified model has an error within only 2%,so the model is accurate.(2)This paper establishes single-pile foundation external application FEM model to research into influential factors like wrapping types,down lead wire connection types and concrete resistivity.Calculation result shows that wrapping radius of flexible planar electrode has obvious influence on grounding resistance;wrapping position of flexible planar electrode has obvious influence on shunt coefficient;down lead wire connection type has obvious influence on dispersal current distribution.(3)This paper establishes four-pile foundation external application FEM model to research into influential factors like wrapping types and distance between piles and calculate typical grounding grids characteristics.According to simulation calculation results,under same conditions,separate wrapping and entire wrapping has a maximum difference of 10Ω.Considering entire wrapping needs additional earth workload and flexible grounding material,engineers are recommended to apply separate wrapping.Distance between piles has a little influence on grounding characteristics.(4)This paper researches into resistance reduction rate under wrapping condition,the saved length of horizontal extension grounding electrodes under wrapping condition and impulse characteristics under wrapping condition.For 6m long piles with 6m distance between piles and 12m long piles with 6m distance between piles,tower foundation external application method has resistance reduction rate of above 20%,and nearly 50%under low soil resistivity.Tower foundation external wrapping method can save more than20m metal grounding electrode and more than 200 m~2 land resources,compared with using extension grounding electrode.This paper’s research conclusions can provide references for design and engineering of tower foundation external application method.This paper has relatively large practical engineering application value.