Today, GL talks about common measures on how to improve the thermal stability of OPGW cables:
1. The shunt line method
The price of OPGW optical cable is very high, and it is not economical to only increase the cross-section to bear the short-circuit current. It is commonly used to set up a lightning protection line parallel to the OPGW optical cable to reduce the current of the OPGW optical cable.
The selection of the shunt line should meet:
a. Have a sufficiently low impedance to make the OPGW current drop below the allowable value;
b. Can pass a large enough current;
c. There should be sufficient strength safety factor while meeting the various requirements of lightning protection.
It should also be noted that although the resistance of the shunt line can be reduced very low, its inductive reactance drops slowly, so the function of the shunt line has a certain limit; Segment selection, but at the transition of the shunt line changing the model section, if the difference between the two sections is large, more current will be distributed to the OPGW cable, which will cause the current of the OPGW cable to suddenly increase. Therefore, when selecting the cross section of the shunt line, the calculation should be repeated.
2. Use of two OPGW cables
For longer lines, because the short-circuit current of the outlet section of the substation is the largest, a larger cross-section OPGW optical cable must be used; for lines far from the substation, a smaller cross-section OPGW optical cable should be used. Two types of shunt lines should be considered when selecting two types of OPGW 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 substation underground, which can significantly reduce the current of the incoming line blocking OPGW optical cable.
4. Multi-circuit lightning protection line parallel method
Connect the grounding devices of several terminal towers, so that the short-circuit current flows into the substation along the multi-circuit lightning protection lines, so that the single-circuit current is greatly reduced. If the thermal stability of the second-grade OPGW optical cable is not 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.