Study On The Grounding Electrode Impulse Current Dispersion Efficiency Factors And Multi Frequency Combination Method

Transmission line tower grounding device is an important discharge channel,when lightning strikes the transmission lines.It is of great significance to study optimization of grounding device structure and reducing tower grounding device grounding resistance for reducing the lightning trip out rate of transmission lines.Transmission line towers distributed in complex terrain,the conventional impulse current generator cannot carry out field test.It is of great significance for the lightning protection of power system to accurately measure the impulse grounding resistance and obtain its change.Firstly,establishing 500kV simulation model of typical tower grounding through simulation found that:the impact leakage resistance is used to research tower grounding device diffuser capability and it puts forward to the basis which can be used for determining the effective diffuser length of the grounding device.By analyzing the relationship between the soil resistivity and the effective bulk flow length,the formula for calculating the effective length of scattered flow is introduced.In addition,it is found that the lower the soil resistivity is,the shorter the effective dispersion length is.The optimal layout of grounding device is studied.In the case of the total rays’ length determined,when it is less than the total rays’ effective diffuser length,the impact resistance extending a single ray’s length less than that increasing the ray’ s number.When the total length of the ray is higher than the total rays’effective bulk flow length,the conclusion is the opposite.Secondly,this paper establishes simulation model of typical tower grounding device to study the influence scope of different length vertical rod,the number and length of vertical grounding electrodes influence on resistance reducing effect.Through the study found that the different length of the vertical rod affects different area--the influence scope of 10 meter vertical rod is about 40m,however,the influence scope of 3m and 5m vertical rod is about5m and 20m respectively;When the total length of vertical grounding electrode under the same condition,the length of the vertical rod is longer,the resistance reduction effect is the better;With the increase in the number of vertical grounding electrodes,the Resistance-reducing Ratio is always saturated.This paper recommended that adding as much as possible long vertical rod at the place which the leakage current is weak,then according to the vertical rod’s impact area to increase the right number of vertical rod.Thirdly,this paper establishes simulation model of typical tower grounding device to study the Soil resistivity,soil replacement method and soil replacement scope influence on resistance reducing effect.Through the study found that the soil resistivity change soil used to lower,the better the resistance reduction effect;Local soil replacement for the grounding device’s four external rays can play a very good effect of the resistance reduction,the recommended soil changing depth is 1.1m,the soil changing total width is 6m.Finally,this paper studies on the method of measuring impulse grounding resistance by multi frequency combination method.Based on the principle of Fourier transform,this paper studied the methods of measuring the grounding impedance.The deviation between the method and the finite element calculation result is analyzed by simulation,and the number of frequency points needed for the measurement of the lightning current is given.Finally,the experimental results show that this method is consistent with the direct impact power measurement results.The experimental results show that under the same measuring connection mode,impact device measurement and using the method provided in this paper to measure,the measurement results are basically consistent.