What are the main factors of electric corrosion of ADSS cable fittings?

2020-01-08 09:13:23 150

With the extensive use of optical cable, the main factors of dry band arc corrosion of ADSS optical cable gradually exposed its own defects, which restricted its further development. The most prominent is the phenomenon of electric corrosion, mainly including electric trace, corrosion and breakdown. The main cause of this phenomenon is "dry belt arc".



At present, the whole country and even the world have carried out relevant research on it. Since the ADSS cable fittings are installed between the high-voltage conductor and the ground wire, on a certain span of the transmission line, the cable is between the high-voltage conductor and the ground wire, and the sheath surface has induced voltage. The cable is in the strong electromagnetic field around the conductor, and the capacitance C3 coupling between the cable and the earth makes it in the space potential position.



The distance between the cable and the conductor is the same as the grounding, and the leakage current of each point on the cable surface and the end of the grounding hardware changes greatly. In November 2007, 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 the induced voltage near the end of the hardware installed in the tower rapidly approaches 0, the earth leakage current increases, and the earth leakage current at the end of the earth hardware reaches the limit value. This length is most likely to produce conditions such as galvanic corrosion, so it is called "effective length".



The surface of each "effective length" fiber optic cable will be polluted in varying degrees and the accumulation of suspended particles in the space will form a resistance layer in a humid environment. Under the conditions of external light, wind and other factors and the resistance layer heating itself, the water on the surface of the optical cable evaporates, the humidity decreases, the resistance layer is partially open, and a dry impetuous band is randomly formed to block the leakage current. When the potential at both ends of the drying area is high enough, an arc will form. When the induced electric field near the drying area is strong enough, the current flows through the surrounding air, forming a discharge arc to the ground, forming the so-called "drying area arc".



The arc generated when the width of the drying zone is about 10 mm has the maximum destructive force. The high heat produced by the arc can make the local temperature of the cable sheath > 500 ℃, which leads to the deterioration of the surface of ADSS cable fittings and the generation of leakage traces. The worst case is that the sheath is burned through. Such repeated discharge, the high-energy particles generated by the discharge arc impact the sheath and other insulating materials, resulting in molecular chain fracture, loss of binding force and its original characteristics, aging and charring of the sheath material, forming a carbonization channel, leaving corrosion traces on the sheath. Under the action of electric corrosion, the surface of optical cable sheath material is rough and hydrophobic. With the aggravation of electric corrosion, tree like electric traces appear in the sheath of optical cable. Finally, the mechanical and physical properties of the material are destroyed or melted to form a cavity, exposing the core of the cable.