Research On Strong Polarization Detection Method Of Grounding Grid Corrosion

As an important part of the power system,the grounding grid is an important condition for ensuring the normal operation of the power system and the safety of power workers.In view of some shortcomings of the current grounding grid corrosion detection methods,this paper proposes a strong polarization method with the advantages of live measurement,strong anti-interference ability,quick and easy measurement,etc.,by measuring the injection current between the grounding grid and the soil,etc.The time constant τ of the electric double layer capacitor discharge is used to evaluate the corrosion degree of the grounding grid as a whole.Based on the school’s self-built large grid,Rizi grid,Kouzi grid,and DC accelerated corrosion test platform,this paper conducts related research on the strong polarization method,including:(1)Aiming at the problem that the fitting results of the strong polarization method are affected by the selected data,the fitting results after discarding different data points are compared and analyzed,and the selection interval of the fitting data is studied.Through many experiments,the influence of injection current amplitude,pole distance,injection current frequency,and injection current position on the time constant τ has been explored.A long-term tracking experiment was carried out to study the corresponding relationship between the time constant τ measured by the strong polarization method and the corrosion of the grounding grid.According to the results of the long-term tracking experiment,the influence of weather factors on the time constant is analyzed,and the conclusion is obtained that the change of rainfall causes the change of the injection current amplitude to affect the time constant τ,and the injection current amplitude is positively correlated with the time constant τ.(2)A cross-validation study of strong polarization method was carried out.A LR(Q(C))equivalent circuit model is established to describe the interface state between the grounding grid and the soil by the AC impedance method,where Q is the constant phase angle element proposed in electrochemistry,and Q is connected in parallel with C and then connected to L and R in series.The change trend of the AC impedance method parameter C and the strong polarization method parameter τ of the anode flat steel,anode flat steel and the earth grid is compared and analyzed,and the conclusion that the strong polarization method has more engineering practical value is obtained.(3)A joint judgment method is proposed to evaluate the overall corrosion of the grounding grid through the two parameters of the ground resistance R and the time constant τ.Through many experiments,it is obtained that the ground resistance R can be measured by the strong polarization method within a certain error range in conclusion.The measurement results of the strong polarization method of the four substations in Zhaotong,Yunnan were compared,and the time constant τ was normalized by the flat steel length and the current influencing factors were corrected.It is concluded that the longer the commissioning time,the smaller the relative change rate δ of the time constant.Based on the experimental data,a preliminary method for judging the overall corrosion state of the grounding grid based on whether δ is less than-50% and whether R is abnormal is proposed.