As it is usually necessary to erect the OPGW optical cable on the top of the tower pole: Although many construction units have considered the installation of lightning protection grounding wires for the tower poles of all levels of lines, how to correctly and reasonably design and install the optical cable at the position of the gantry The grounding drain wire, but did not seriously consider. The OPGW optical cable should be suspended in the air at the terminal tower and substation gantry. Sometimes, this phenomenon is easily overlooked by the staff. If there is a short circuit or lightning strike, a large current will be generated and passed in the OPGW optical cable. If the current exceeds the capacity that the optical cable can withstand, the optical cable will be blown or damaged, which will cause communication service interruption and affect the power grid. safe and stable operation.
Not far from the substation, the grounding problem occurred because the construction device accidentally touched the line. In addition, in the structure of the substation, the OPGW optical cable was almost blown, which affected normal communication.
Analyze the reason: a large current exists in the short circuit of the wire, and passes through the ground wire and the tower, and at the same time, a part of the current also passes through the OPGW optical cable. As shown in the figure above: the OPGW optical cable is insulated with frame and ground wire insulators. However, when the OPGW optical cable is set along the frame, it will touch the grounding member, but because the grounding condition is not stable, when there is current passing through, an arc will definitely occur
In order to bring out the lightning conduction and current shunting functions of the optical cable, one end of the grounding wire is usually connected to the OPGW with a parallel trench clamp, and the parallel trench clamp should be used to complete the grounding of the OPGW. It is necessary to use the OPGW down conductor card of the insulated substation, and use the structure insulation and insulating rubber pad to complete the insulation treatment of the joint box and the hoop of the remaining cable rack. Use parallel trench clamps on the top of the optical cable splice box and the top of the door frame to complete the grounding process.
2. Apply reasonable grounding measures
In order to reliably complete the grounding of the OPGW, the top of the frame, the fixed point at the lower end (in front of the remaining cables) and the end of the optical cable are respectively connected to the frame by matching dedicated grounding wires. Matching fixtures and insulating rubber should be used to fix the remaining cable racks, splicing boxes and the frame. When installing the ground wire, it is necessary to ensure that the length is moderate, prevent twisting or hard bending, and be beautiful and smooth. Correctly and reasonably complete the processing of the connection part to ensure that the entire line is consistent. The correct grounding of the OPGW should be done using a specific grounding wire, and when grounding, a single application of fittings should be prevented. In order to ensure that the frame and OPGW are very firmly connected together and eliminate the discharge problem in the frame and OPGW, at this time, the down-lead clamp with insulating pad should be applied to the OPGW under the frame. And, the distance between the frame member and the OPGW is controlled to be more than 20 mm.
Through the experience summed up in the actual work, we obtain the following arguments: the OPGW drop cable in the frame and substation needs to be firmly connected. There are two points that must be paid great attention to when connecting the structure and OPGW: the top of the remaining cable and the upper part of the structure; at the same time, in order to ensure its stability, the structure must complete a stable electrical connection with the end of the OPGW optical cable. In order to show the excellent conductive function and reasonable shunt effect, and to ensure that the grounding wire can be quickly opened when measuring the grounding resistance of the substation, a special grounding switch and grounding wire should be applied to the OPGW optical cable, and then grounded The terminals are completely and correctly connected. Provide the parallel trench clamp for OPGW to complete the corresponding grounding installation, and connect the sides of the frame with bolts to prevent welding by electric welding. On the basis of the relevant regulations when designing the circuit, the insulation gap between the ground wires is controlled between 18-20 mm. OPGW optical cables are not only ground wires, but also optical cables. In addition, through the above methods, after the structure is correctly connected with the OPGW optical cable, there will be a very small voltage between the two, so it is necessary to set the structure components and OPGW down-conductor optical cables above 20 mm Pitch. In many 220KV and 110KV substations of the power sector, this optical cable grounding method is also actively applied. The connection between metal-free optical cables and OPGW is realized at the terminal, and the substation is connected and processed by erecting ADSS cables or direct burying of pipelines. Gantry and terminal towers. However, both overhead laying and underground burial of ADSS cables have certain limitations. For example, the route between the power station wall and the terminal tower and the land acquisition situation need to be carefully analyzed and considered. Land acquisition and excavation of traditional lines are difficult. Because sometimes electromagnetic compatibility problems will exist in high electromagnetic fields, so it is not suitable to apply ADSS cable erection on transmission lines or 500kv lines. Influence.
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