| Transmission line tower grounding is of crucial importance to the safety and stability of power system. When tower or grounding wire is under lightning strike, current resulted by the strike flows into earth through tower grounding connection, back strike voltage with considerably great magnitude would be presented as a result of the somewhat large tower grounding resistance. Statistically, the lightning strike incidences due to the ineffective tower grounding account much for transmission line failures.In mountain areas where earth resistance is relatively high, transmission line tower grounding resistance can not be made to meet the requirements in regulations easily, then many unconventional measures must be carried out to lower the resistance. In this paper, we deal with a typical transmission line as an experimental project, after theoretical analysis, simulation, calculation and field experiments, a series of practical and economical measures are presented. So the work of this paper is of theoretically and practically importance in making sure power system reliability and personal safety.After a mass effort of field survey, the basic condition of 110kV Nanzhongqian transmission line was clear. In consideration of transmission line terrain, tower grounding connection, tower space and tower type, the factors account for the high resistance and the comprehensive measure to lower the tower it were studied. The results are of referential value to designing or improving tower grounding connection in areas where soil resistivity is high.Two method to reduce the tower grounding resistance in high earth resistivity areas are brought forward in this paper. One is to use the SZJ hollow grounding device which can reduce the soil "resistivity of the earth and rock around it to realize the reduction of grounding resistance. The other is to add conductive cement to tower base. The best technics in using the SZJ hollow grounding device and the conductive cement in high soil resistivity mountain, hill or drought areas is deduced after theoretical analysis, calculation and field experiments. Following this technics, the lowest cost and the largest reduction in grounding resistance can be realized.In application of research results in this paper, the design and improvement of 110kV Nanzhongqian transmission line tower grounding connection is completed and tower grounding resistance are made to meet the concrete requirements in DL/T621-1997 << AC electrical connection grounding... |
