The Study On Method And Test To Measure Tower Grounding Resistance With Shorter Electrode Wire

Tower grounding device is an important grounding protection facility of transmission line.Only the tower grounding device with good grounding performance can reduce the power accidents caused by grounding fault and ensure the stable operation of power system.The grounding resistance is an important technical index to assess the grounding performance of tower grounding device.Only small value of grounding resistance can ensure the fault current discharge into soil effectively from tower grounding device to the occurrence of the power accident.Therefore,the regular measurement of the grounding resistance becomes an important work for the transmission line operations.At present,The measurement methods with distribution electrodes,mainly including Fall of Potential Method and 0.618 method,are widely used In actual engineering.The conventional electrode distribution measurement method is to obtain the grounding resistance by measuring the potential difference between the grounding device and the grounding reference point after theoretical analysis of the potential relationship between the groundingdevice andthe ground reference point.The theoretical core of traditional grounding resistance measurement method is to accurately calculate the position of potential reference point by reasonable physical model assumption,which determines the longer leadwire.In practical engineering,the lead length of 0.618 Method requires 4 times of the length of the scattering grounding electrode.Aim at the the problem of long lead wire length in the existing grounding resistance measurement method which can’t be applied to the complex terrain,this paper proposed a method to measure tower grounding resistance with shorter electrode wire based on Green’s Theoremafter analyzing and abandoning the technical bottleneck of the existing grounding resistance measurement theory.The method can effectively shorten the length of lead wire to 2 times of the length of the scattering grounding electrode during the measurement of grounding resistance and enhance the adaptability of measurement method under the requirement of ensuring measurement accuracy.This paper first analyzes the technical limitations of the conventional tower grounding resistance measurements which are unable to realize the measurement with short electrode wire.Then the importance of putting forward a new measurement theory which can realize the measurement with short electrode wire expounded.The physical model of tower grounding device and the potential equations around the grounding device are established.Injection current and reflux current are considered,the equipotential surface distribution and potential calculation is analysed.Location of Green’s Boundary reference point and zero potential point are studied in detail.Finally,the method to measure tower grounding resistance with shorter electrode wire is given.The results show that the proposed method can greatly shortens the length of electrode wire with high precision.The main contents of this paper are as follows:(1)Based on the theoretical calculation and simulation analysis,the technical limitations of the existing measurement theory on the lead wire length is studied.It is concluded that the best distribution method is to distribute the current electrode amoung the grounding device and potential electrode if utilizing the existing grounding resistance measurement theory.It demonstrates that a new grounding resistance measurement theory should be proposed to shorten the lead wire length.(2)The potential equation of tower grounding device is established based on Green’s Theorem.Then the Green’s Boundary condition of the field where the tower grounding device locates is analyzed,and the distribution of bulk charge in the field is studied.The spatial potential distribution under the influence of injection current and reflux current separately and the spatial potential distribution under the simultaneous influence of injection current and reflux currentarestudied.According to simulation results,the distribution of the zero potential point during the measurement is obtained and the calculation expression of the soil potential under the influence of the reflux current is analyzed.(3)The best way to distribute the electrodes and the position of Green’s Boundary reference point are studied.After then the method to measure the tower grounding resistance with shorter lead wire is presented.Different simulations of tower grounding device are established to make example analysis and the field test is carried out.The results show that the method to measure tower grounding resistance with shorter electrode wire based on Green’s theorem can accurately measure the tower grounding resistance with shorter lead wire.