Research Of Stray Current Corrosion On Substation Grounding Device And Its Simulation

With the rapid increase of China's electricity consumption, power system capacity continues to expand, but also to further increase network capacity, which puts forward higher requirements for the safe and stable operation of transformer substation. As an important part of the substation, grounding device, which is used to discharge current for electrical equipments, is buried perennially, in addition to suffering the chemical corrosion and electrochemical corrosion in the soil, but also withstanding the stray current corrosion. Good anti-corrosion of grounding device, can not only ensure its service life, but also guarantee the safe and stable operation of the substation. Some results have achieved for research on the corrosion of substation grounding device so far, however, researches on stray current corrosion of grounding device have been barely reported. And the damage of stray current corrosion is huge, which can directly lead to trip of electrical equipments and even cause the entire power outage, etc. Therefore, study on stray current corrosion of substation grounding device has become an important and urgent research topic.The stray current of substation grounding device was mainly studied from three aspects in the thesis. Firstly, Regarding the metal Q235 as research subject, based on the simulated corrosion state of indoor stray current to the substation grounding device, the influences of AC(alternating current) current density, power-on time, soil pH and AC frequency on the AC stray current corrosion process were investigated by weight loss and electrochemical analysis techniques. Secondly, electromagnetic simulation capabilities of ANSYS software were used to simulate the potential distribution of substation grounding grid space around. The influence of azimuth, soil resistivity, discharge current, and distance between metal pipes on the potential distribution were researched by potential distribution nephograms and curves. Finally, numerical calculation method was used to simulate the ground potential distribution of substation grounding device by MATLAB software. Green's function calculation principles was used to establish a mathematical model of ground potential distribution which was analysised in different specifications uniform grid by the potential distribution matrixs, 3D figures, etc.Research on the AC stray current corrosion of substation grounding grid showed that the AC stray current generated around the substation grounding grid could intensify the metal corrosion, the corrosion of stray current to substation grounding metals aggravated with the enhancing of AC current density; the corrosion rate of AC stray current increased firstly and then decreased with the increasing of operation time; acidic environment worsened the corrosion of AC stray current, nevertheless, it was hindered in alkaline environment. The AC frequency fluctuating within a narrow range had minor effect to the corrosion of AC stray current on grounding metals.Research on the potential distribution of substation grounding grid space around simulated by ANSYS software showed that ANSYS software could accurately simulate and analyze the potential distribution. The potentials parallel with the grounding grid metal pipe were almost the same everywhere; the potential difference between the center of the metal pipe and its both ends increased with the increasing of azimuth; the potential difference reached maximum when both of the metal pipe was vertical; the increasing of discharge current could promote the potential value of substation grounding grid space around; the influence of soil resistivity on the potential distribution was greater, the higher the soil resistivity, the higher the potential, and the potential decreased from the center to both ends; nervetheless, the bigger the distance between two metal pipes, the lower the potential.Research on the numerical calculation of substation grounding grid ground potential showed that the potential distribution is that potential presented relatively high at the mesh nodes and relatively low at the center of grids for 5×5 uniform grounding grid; the potential reduced out of the grid; the highest potential presented at the nodes of the center grid and the lowest at the center of the grid near the four corners; the difference of the two reached 13.53V; the potential distribution is consistent with that of 5×5 uniform grounding grid for 10×10 uniform grounding grid; and the difference reached 51.59V; the bigger the soil resistivity, the ground potential of the substation grounding grid.