What is the reason for the sunset of the optical cable line, and how to prevent the sunset of the optical cable line? Let's take a look with the cable experts!
What are the reasons for the sunset of optical cable lines
Optical fibers are non-conductive and can be protected from surge currents. However, in order to protect high-capacity optical fibers from environmental events (such as animal bites, collisions with rocks, overhead metal accessories, shotgun damage, and other natural and man-made events, etc.), optical cables must have armored components, mainly Metal armor layer, reinforced core and business copper wire, etc., they are all metal conductors. When the power line is close to short circuit or lightning strikes metal components, alternating current or surge current will be induced, which will harm personal safety or damage line equipment.
Lightning has a tendency to find the path of least impedance to discharge thundercloud charges and neutralize underground opposite charges. When lightning strikes the nearby ground or buildings, the potential of the lightning strike point rises, and the optical cable extends far away, and the remote potential can be regarded as O, so the optical cable potential near the lightning strike point is also regarded as O. In this way, a huge potential difference is formed between the lightning point and the optical cable. If this potential difference exceeds the compressive strength between the lightning point and the outer sheath of the optical cable, it will break down the outer sheath and form a gap from the lightning point to the metal component. The arc channel causes a large amount of lightning current to flow to the optical cable, causing serious damage to the optical cable.
During the construction of the optical cable line, it is inevitable to damage the PE (polyethylene) sheath. In addition, rat bites, external forces, etc. may cause the metal components in the optical cable to be exposed. These exposed points are easy to introduce strong electricity or lightning charges into the cable, causing damage.
How to prevent the sunset of optical cable lines
Lightning protection for optical cable lines can be carried out in a targeted manner according to natural conditions such as local weather and terrain. Through the analysis of several cases of optical cable lightning strike faults, we found that the following problems should be paid attention to in the construction and maintenance of optical cable lines.
(1) For overhead optical cables:
①The joint box usually has a structure in which the reinforcing core can be disconnected and connected. Regardless of the electrical connection or disconnection method, the metal platen connection structure is better than the screw connection, and the screw bolt horizontal opening is better than the longitudinal slotting structure. This is the choice Problems that should be paid attention to when connecting the box.
② The overhead suspension wires should be electrically connected and grounded every 2km. When grounding, it can be grounded directly or through a suitable surge protection device. In this way, the suspension wire has the protective effect of the overhead ground wire.
(2) For the lightning protection of rational optical cable lines:
① In the local grounding mode, the metal parts in the optical cable should be connected at the joints, so that the reinforced core, moisture-proof layer, and armored layer of the optical cable in the relay section remain connected. Staggered layers are installed in the bureaus (stations) at both ends, the reinforcements should be grounded, and the moisture-proof layer should be grounded through arresters.
②For optical cables without business copper wires, in accordance with the provisions of YDJ14-91, the moisture-proof layer, armor layer and reinforcing core at the optical cable joints should be electrically disconnected, and they are not grounded, and they are insulated from the ground, which can avoid optical cables. The accumulation of induced lightning current in the medium can also avoid the lightning current in the ground being introduced into the optical cable by the grounding device due to the difference in the ground loop impedance of the lightning protection drain line and the metal components of the optical cable. Practice has proved that this method is simple and effective, because under normal circumstances, the metal components in the optical cable (without poor insulation points and joints entering water) have a high insulation value to the ground, and the lightning current is not easy to enter the optical cable.
③The grounding device of the terminal box must be good, and the grounding resistance must meet the requirements. Because the terminal is grounded, contrary to the analysis in ②, the metal sheath in the optical cable has zero potential to the ground. If the outdoor optical cable has a damaged point in the sheath, the lightning current will easily enter the optical cable under the same conditions. If the grounding device is not good, the lightning current will not be rapid. If you let it go, there will be no protection.
