The researchers who formulated this technical specification conducted on-site investigation and Analysis on the operation failure of OPGW downlead in this case. After investigation and analysis of actual cases and simulation experiments, many enterprises and relevant departments have formulated repair measures for OPGW technology. These measures mainly follow the following principles: first, when the OPGW cable hardware is short circuited or struck by lightning, the current can enter the ground smoothly without burning the OPGW; second, there is no contact between the external connector and the frame metal body, which eliminates the hidden danger of discharge between the OPGW external body and the frame metal. The main technical methods are as follows.
(1) Prevent water from seeping into the protective iron pipe. In order to achieve the above purpose, the pipe head shall be sealed with a sealing cap and a fire-resistant mud. The diameter of the sealing cap here must be the same as the diameter of the down lead iron pipe, and some glass glue or foaming agent materials shall be filled in the gap.
(2) When the OPGW enters the substation frame, the connection between the OPGW and the grounding grid connection point at the top of the substation frame must be connected with the grounding wire. For the grounding wire, not only its cross-sectional area and OPGW cross-sectional area, but also the metal connection surface between the grounding wire and the grounding grid shall be smooth to ensure good conductivity after connection.
(3) Lead down the appropriate position between the OPGW junction box and the top OPGW grounding point, and use the grounding wire to connect the OPGW with the grounding grid (transverse metal platform assembly grounding grid) in the substation reliably. In the connection, the connection section and OPGW cable fittings are the same, and the surface of the connection must be flat. After ensuring good conductivity, another reliable connection between OPGW and substation grounding grid can also be ensured.
(4) The effective contact area of the ground wire with severe arc burn is very small. If the effective contact area data of suitable ears cannot be calculated, the ears with larger contact area must be used.
(5) Due to the diversity of substation building types, the connection positions of grounding wires are also diverse. In this case, how to ensure the connection mode between OPGW ground wire and substation grounding grid has become the concern of technicians and researchers.