The cable is in the strong electromagnetic field around the conductor, and the capacitance coupling between the cable and the earth makes it in the space potential position. Under the action of space potential, the wet or dirty (inevitable) surface of optical cable will generate ground leakage current and heat. The heat evaporates the water on the surface of the optical cable and forms a drying belt randomly (uncontrollably) to block the surface leakage current. When the potential at both ends of the drying belt is high enough, the discharge forms an arc (called "dry charged arc"). The basic condition of electric corrosion is a certain leakage current and enough high space potential.
The earth leakage current is driven by space potential. In a certain span of transmission line, if the distance between the optical cable and the conductor is the same (the same sag), and the distance between the optical cable and the ground is the same (in fact, this is impossible, just assumed), the distance between each point on the surface of the ADSS Optical cable hardware and the end of the grounding hardware varies greatly. Although the induced voltage of the span center is very high, the charging constant is very large, the charging current is very small, and there is no leakage current on the surface of the optical cable. When it is close to the end of the tower hardware, the induced voltage tends to zero sharply and the leakage current increases. When the leakage current of grounding hardware terminal reaches the maximum value, electric corrosion will occur if the arc condition is met. The distance from a point where the earth leakage current begins to increase to the end of the fitting is called the "effective length", which is the most dangerous area of galvanic corrosion. Therefore, there are two effective lengths in a span. The influence of double loop phase on the suspension point of optical cable is affected by the phase arrangement of three-phase conductor, the influence of single loop phase change is less, and the influence of double loop phase change is greater. In the double loop system, as far as the installation space of ADSS cable hardware is concerned, ABC-ABC phase is the smallest, and other phases have different degrees of expansion, especially abc-cba phase. For the suspension point, due to the power failure on one side, the single circuit operation of the double circuit line is more complex, and the space potential may be smaller or larger. In addition to the phase effect, when the suspension point of optical cable is fixed, its space potential will also be affected by the diameter of conductor and ground wire, conductor splitting, hardware and cable wind swing and other factors.
Electric corrosion control: all electric corrosion faults occur in the "effective length" area, so the control range is also concentrated in the effective length area.