Corrosion Detection and Analysis of the Underground Grounding Grid in a 220kv Transformer Substation

The first corrosion detection for the large grounding grid of a 220kV substation was performed based on electrical impedance tomography (EIT) technology. The impedance value of grounding grid branch which represented the corrosion state of metal was calculated using the current and voltage data acquired on-site through injecting a direct current from one down conductor and collecting voltage data from other down conductors. The results indicated that the impedance increase ratio of the No.143 grounding grid branch in test area D was higher than the warning value (>15 times), indicating a breakage has occurred on this grounding grid branch. The two-dimension corrosion image of the whole underground grounding grid was calculated and drawn accurately and visually using the corrosion diagnosis software. The corrosion rate of carbon steel was monitored in the serious corrosion area later, to realize the online corrosion monitoring of grounding grid metal. EIT technology realized the underground grounding grid statues visible exhibition, and could be used to detect the corrosion state, corrosion area and failure location of the underground grounding grid rapidly and effectively. This could reduce the blindness of corrosion detection for grounding grid and provide guidelines on the corrosion maintenance of underground grounding grid in large substation.