Common measures to improve the thermal stability of OPGW optical cable:
1. shunt line method
The price of OPGW optical cable is very high, and it is uneconomical to bear the short-circuit current only by increasing the cross-section. The method of erecting a lightning conductor parallel to the OPGW optical cable is commonly used to reduce the current of the OPGW optical cable.
The selection of shunt line should meet the following requirements:
a. Have a low enough impedance to make the OPGW current drop below the allowable value;
b. Can pass a large enough current;
c. While meeting the requirements of lightning protection, there should be sufficient strength safety factor.
It should also be noted that although the resistance of the shunt line can be reduced very low, its inductance decreases slowly, so the role of the shunt line is limited; Segmental selection, but at the transition point where the shunt line changes the model section, if the difference between the two sections is large, more current will be distributed to the OPGW optical cable, which will cause the current of the OPGW optical cable to rise suddenly. Therefore, the cross-section of the shunt line should be checked repeatedly.
2. Combined use of OPGW optical cables of two specifications
For longer lines, since the short-circuit current at the exit section of the substation is the largest, OPGW optical cables with larger cross-sections must be used; lines far away from substations should use OPGW optical cables with smaller cross-sections. Two kinds of shunt lines should be considered when choosing two kinds of OPGW optical cables.
3. Underground diversion method
Connect the grounding device of the terminal tower with the grounding grid of the substation with several round steels with appropriate cross-sections, so that part of the short-circuit current enters the underground of the substation, which can significantly reduce the current of the incoming line blocking OPGW optical cable.
4. Parallel connection method of multi-circuit lightning conductors
Connect the grounding devices of several terminal towers, so that the short-circuit current flows into the substation along the multi-circuit lightning conductor, so that the single-circuit current is greatly reduced. If the thermal stability of the second-grade OPGW optical cable is not yet reliable, the grounding device of the second base tower can be connected, and so on. However, it should be noted that relay zero-sequence protection should be considered when connecting multiple towers.