How to Protect Fiber Optic Cable From Lightning?

BY Hunan GL Technology Co.,Ltd.

POST ON:2021-05-18

VIEWS 54 Times

As we all know that lightning is a discharge of atmospheric electricity that is triggered by a build-up of differing charges within a cloud. The result is a sudden release of energy that causes a distinctive bright flare, followed by a thunderclap.

For example, it will not only affect all DWDM fiber channels in short bursts, but also affect transmission directions simultaneously according to numerous researches. It will even cause a fire when there are high current lightning discharges. Although the signals in fiber cables are optical signals, most of the outdoor optical cables using reinforced cores or armored optical cables are easy to get damaged under lightning because of the metal protective layer inside the cable. Therefore, it is important to build a lightning protection system to protective optical cables.

Measure 1:

Lightning protection for straight-line optical cable lines: ①In-office grounding mode, the metal parts in the optical cable should be connected at the joints, so that the reinforcing core, moisture-proof layer and armor layer of the relay section of the optical cable are kept in a connected state. ②According to the regulations of YDJ14-91, the moisture-proof layer, armor layer and reinforcing core at the optical cable joint should be electrically disconnected, and they are not grounded, and they are insulated from the ground, which can avoid the accumulation of induced lightning current in the optical cable. It can avoid that the lightning current in the earth is introduced into the optical cable by the grounding device due to the difference in the impedance of the lightning protection drain wire and the metal component of the optical cable to the ground.

Soil Texture Lightning Protection Wire Requirements for General Poles Wire Requirements for Poles Set at the Junction of High Voltage Power Transmission Lines
resistance (Ω) extension (m) resistance (Ω) extension (m)
Boggy Soil 80 1.0 25 2
Black Soil 80 1.0 25 3
Clay 100 1.5 25 4
Gravel Soil 150 2 25 5
Sandy Soil 200 5 25 9

Measure 2:

For overhead optical cables: overhead suspension wires should be electrically connected and grounded every 2km. When grounding, it can be directly grounded or grounded through a suitable surge protection device. In this way, the suspension wire has the protective effect of the overhead ground wire.

Soil Texture Common Soil Gravel Soil Clay Chisley Soil
Electrical Resistivity (Ω.m) ≤100 101~300 301~500 >500
Resistance of the Suspension Wires ≤20 ≤30 ≤35 ≤45
Resistance of the Lightning Protection Wires ≤80 ≤100 ≤150 ≤200

Measure 3:

After the optical cable enters the terminal box, the terminal box should be grounded. After the lightning current enters the metal layer of the optical cable, the grounding of the terminal box can quickly release the lightning current and play a protective role. The direct-buried optical cable has an armor layer and a reinforced core, and the outer sheath is a PE (polyethylene) sheath, which can effectively prevent corrosion and rodent bites.




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