Today, GL talks about the common measures of how to improve the thermal stability of OPGW cable:
1: Shunt line method
The price of OPGW cable is very high, and it is not economical to simply increase the cross-section to bear the short-circuit current. It is commonly used to set up a lightning protection wire parallel to the OPGW cable to reduce the current of the OPGW cable. The selection of the shunt line should meet: a. There is a sufficiently low 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 a sufficient strength safety factor. 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 role of the shunt line has a certain limit; the shunt line can be based on the short-circuit current situation around the line Sectional selection, but at the transition of the shunt line to change the model section, if the two sections have a large difference, more current will be distributed to the OPGW cable, which will cause the current of the OPGW cable to increase suddenly. Therefore, the cross-section of the shunt line should be checked repeatedly.
2: Parallel usage of OPGW cables of two specifications
For longer lines, due to the largest short-circuit current at the outlet section of the substation, a larger cross-section OPGW cable must be used; the line away from the substation uses a smaller cross-section OPGW cable. Two types of shunt lines should be considered when selecting two OPGW cables.
3: Underground diversion method
Connect the grounding device of the terminal tower and the grounding grid of the substation with several round steels with appropriate cross-sections, so that a part of the short-circuit current enters the substation underground, which can significantly reduce the current of the OPGW cable.
4: Parallel method of multi-circuit lightning protection lines
Connect the grounding devices of several terminal towers to make the short-circuit current flow into the substation along the multi-loop lightning protection line, so that the single-circuit current is greatly reduced. If the thermal stability of the second-grade OPGW cable is not reliable, the grounding device of the second base tower can be connected, and so on. But it should be noted that the relay zero sequence protection should be considered when connecting multiple towers.
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