We all know the function of optical cable, and the sunset of optical cable line is often confusing, and we don't know the reason, let alone what to do. Today, the editor will talk about what is the reason for the sunset of the optical cable line, and how to prevent the sunset of the optical cable line.
What are the reasons for the sunset of the optical cable line
Optical fibers are non-conductive and protected from inrush currents. But in order to protect the high-capacity fiber from environmental events (such as animal bites, collisions with rocks, overhead metal attachments, shotgun damage, and other natural and man-made events, etc.), the fiber optic cable must have armored components, mainly including Metal armor, reinforcement and service copper wire, etc., they are all metal conductors. When the power line is close to a 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 with the least impedance to discharge the thundercloud charge and neutralize the underground charge of the opposite sex. When lightning strikes the nearby ground or building, the potential of the lightning point rises, and the optical cable extends far, and the potential at the far end can be regarded as O, so the potential of the optical cable 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, the outer sheath will be broken down, forming a connection from the lightning point to the metal member. The arc channel causes a large amount of lightning current to flow into the optical cable, causing serious damage to the optical cable.
The PE (polyethylene) sheath is inevitably damaged during the construction of the optical cable line. In addition, rat bites and external forces may cause the metal components in the optical cable to be exposed. These exposed points are easy to introduce strong electric or lightning charges into the cable, causing damage.
How to prevent the sunset of optical cable lines
Lightning protection of 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 strikes, we found that the following problems should be paid attention to in the construction and maintenance of optical cable lines.
(1) For aerial optical cable:
①The junction 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 pressure plate connection structure is better than the screw bolt connection, and the horizontal opening of the screw bolt is better than the longitudinal slot structure. Problems that should be paid attention to when connecting the box.
②The overhead suspension wire 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 the rational optical cable line:
①In the way of intra-office grounding, the metal parts in the optical cable should be connected at the joint part, so that the reinforcing core, moisture-proof layer and armor layer of the optical fiber cable in the relay section are kept connected. The layers should be staggered in the bureaus (stations) at both ends, the reinforcement should be grounded, and the moisture-proof layer should be grounded through the arrester.
②For the optical cable with no service copper wire, according to the regulations of YDJ14-91, the moisture-proof layer, armor layer and reinforcing core should be electrically disconnected at the optical cable joint, and they are not grounded and are insulated to the ground, which can avoid the optical cable. The accumulation of induced lightning current can also avoid the introduction of lightning current into the optical cable from the grounding device due to the difference in the impedance of the lightning protection drain line and the metal components of the optical cable to the ground loop. Practice has proved that this method is simple and effective, because under normal circumstances, the metal components in the optical cable (without poor insulation and water in the joint) 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 ground. If the outdoor optical cable has a damaged sheath, the lightning current is easy to enter the optical cable under the same conditions. If the grounding device is not good, the lightning current cannot be quickly If you let it go, it won't protect you.
In addition, burying drainage lines and arc suppression lines is also a better lightning protection method. According to the law of lightning strikes, a certain length of flow line (arc suppression line) should be buried in the area prone to lightning strikes according to the requirements (the principle and implementation plan will not be discussed), and be well grounded. The same drain line (arc suppression line) should be selected as much as possible. Low-impedance, corrosion-resistant metal. Practice has proved that this protection method has better lightning protection effect, but the disadvantage is that the cost is higher.
