The main factor causing electrical corrosion of adss optical cables – dry band arc. With the widespread use of optical cables, its own defects are gradually exposed, thus restricting its further development. The most prominent is the electrical corrosion phenomenon, which is mainly manifested as electric traces and corrosion. , breakdown, the main factor causing this phenomenon is “dry band arc”.
Since the optical cable is between the high-voltage conductor and the ground wire after installation, at a certain span of the transmission line, the optical cable is between the high-voltage conductor and the ground wire, and there is an induced voltage on the surface of the sheath. The ADSS optical cable that is under tension during operation is in a strong electromagnetic field that exists in the space around the conductor. The capacitive C3 coupling between the optical cable and the conductor and the earth puts it at a space potential position.
Assuming that the distance between the optical cable and the conductor and the earth remains unchanged, the ground leakage current at each point on the surface of the optical cable and the end of the grounded hardware changes greatly. Although the induced voltage in the center of the distance is very high, the charging constant is very large and the charging current is extremely small. There is no trace on the surface of the optical cable. Leakage current; As the induced voltage approaches the end of the hardware installed on the tower, the induced voltage sharply approaches 0, and at the same time the ground leakage current becomes larger, and the ground leakage current reaches the limit value at the end of the grounded hardware. This length is most likely to cause electrical corrosion and other conditions, so this length is called the “active length”.
The surface of each “active length” optical cable will have varying degrees of pollution and accumulation of suspended particles in space, forming a resistance layer in a humid environment. Under the conditions of external light, wind and other factors and the heating of the resistive layer itself, the water on the surface of the optical cable evaporates, the humidity becomes smaller, the resistive layer is partially disconnected, and dry zones are randomly formed to block leakage current. When the potential at both ends of the dry zone is high enough, a discharge will occur to form an arc. When the induced electric field near the dry zone is strong enough, the current breaks down the surrounding air to form an endpoint discharge arc to the ground, thus forming the so-called “dry zone arc”.
The arc generated when the dry zone width is about 10mm is the most damaging. The high heat energy generated by the discharge arc can cause the local temperature of the optical cable sheath to be >500°C, causing the surface of the sheath to degrade and causing leakage and tracking. In the worst case, the sheath is burned through. Repeated discharges in this way can cause damage to the sheath due to the discharge arc. High-energy particles impact insulating materials such as sheaths, causing their molecular chains to break, losing their binding force and their original characteristics, causing the sheath materials to age and burn, forming carbonization channels and causing corrosion traces. Under the action of electric corrosion, the surface of the optical cable sheath material becomes rough and loses its hydrophobicity. As the electric corrosion increases, tree-like traces appear on the optical cable sheath. Finally, the mechanical and physical properties of the material are destroyed or melted to form a cavity, which is exposed. Take out the fiber optic cable core.
According to data from the West Coast of Hanterstor, Scotland: arcing does not occur when the ground leakage current is <013mA. Therefore, 013mA is recognized as the threshold value at which arc does not occur; when the ground leakage current is about 015mA, arc will occur; as the ground leakage current is >1mA, the arc will become serious; when the ground leakage current is larger (>5mA), the arc will be active. will stop, that is, large current will not produce arc. In addition to dry-strip arcs, electrical corrosion is also directly or indirectly related to the diameter of wires and ground wires, splitting of wires, wind swings of hardware and optical cables, and the tension of optical cables. Through the above analysis, it can be concluded that the electric corrosion phenomenon usually occurs on the surface of the optical cable where the line field intensity distribution changes most rapidly, that is, near the fittings of the optical cable tower hanging point, and the actual location of electric corrosion is consistent with the above analysis.
