Transmission line towers must have reliable grounding to ensure lightning current is conducted into the earth, protecting line insulation. To ensure that lightning current is introduced into the ground without causing harm to line insulation, it is necessary to ensure the entire current path is unobstructed. From previously focusing only on the grounding resistance of the ground grid, the development has been to consider and test the entire lightning current discharge channel as a whole. Practice has proven that contact resistance is a weak link in the tower grounding system. After treatment, the tower grounding system can reduce the back-flashover trip-out rate and improve the lightning withstand level of the tower, which has significant practical significance for line lightning protection.
To ensure that the grounding resistance meets the design value requirements, the operating regulations stipulate that the tower grounding resistance should be measured periodically. The measuring instrument basically uses a four-pole resistance measuring instrument. Under the premise of correct operation methods and allowable geographical environment, it can generally complete the measurement of the ground grid grounding resistance. However, lightning current is discharged into the earth from the top of the tower through the tower body and the ground grid. As shown, when lightning strikes the overhead ground wire of towers 1#—2#, the lightning current will enter the ground along towers 1#, 2#, 3#, 4#, etc.
From the perspective of conducting lightning current, attention should be paid to the resistance of the entire discharge channel, not just the grounding resistance of the ground grid.
