Underground cables are used in cases where aerial transmission is not possible or when overhead lines cause visual pollution. As their name suggests, these cables are laid underground.
These cables are mandatorily used in places where energy cannot be transmitted by air (such as river, sea, and lake crossings).
Cables used in TEDAŞ:
Overhead Lines:
- Swallow; 1 x 50 / 16 mm²
- Pigeon; 1 x 95 / 16 mm²
- Hawk; 1 x 240 / 25 mm²
What Should Be Considered When Laying Underground Cables?
The route (plan) of the cable line to be laid should be determined.
Considerations for Determining the Route Plan:
- The cable route to be laid should be drawn as a straight line. Curved routes should be avoided as much as possible.
- Care should be taken that the passage route does not pass over lines such as rivers, bridges, and railways.
- Considering potential damage from chemical substances, industrial areas should be avoided.
- The laying process should be carried out under pedestrian paths or along wall sides.
- Care should be taken not to mix telephone lines, sewer pipes, water, and gas pipes.
- An electrical connection should be provided to prevent potential damage or moisture.
- When cutting the cable, the conductor ends should be connected to avoid loosening between the conductor and insulation.
- The conductor bundle should not be twisted in the opposite direction of the twist.
- Connection terminals (parts that connect electrical transmission cables to each other) must be compatible with the cable cross-section.
How to Lay Underground Cables?
It is not correct to directly lay cables on the ground soil. The lifespan of cables laid in the soil without protection shortens due to chemical substances in the soil. The depth of the channels where the laying will be done varies depending on the voltage in the current. Channel Depths According to Voltage Ratio:
- 0-1 kV cables should be laid at a depth of 40-50 cm.
- 1-10 kV cables should be laid at a depth of 60-70 cm.
- 10-35 kV cables should be laid at a depth of 80-100 cm.
- High voltage cables should be laid at a depth of 100-120 cm.
The bottom width of the channels opened for underground cables is 40 cm, and the top width is 60 cm. In the case of laying more than one cable in the same channel, the channel width is increased by 10 cm both at the bottom and top for each cable. The distance between cables should not be less than 6 cm. To ensure proper laying, the bottom of the channels should be solid and free of stones.
After the cable laying process is completed, sifted soil or sand should be carefully poured over it to a thickness of 10 cm. To prevent any potential damage, the cables should be protected with materials like bricks or concrete so that there are no gaps between them. After placing the suggested protective materials, the channel is filled with debris, and a warning tape is stretched over it. The soil is compacted with grounding machines or hand tamps. Any damage or disturbance in the surroundings should be repaired.
While connecting the conductors to the area where electrical transmission will be made, cable lugs should be used. Cable heads are divided into internal and external. The purpose of these heads is:
- Internal Connections: To provide protection against potential short circuits and impacts.
- External Connections: To prevent moisture from affecting the cable.
Potential Faults in Underground Cables:
- External influences,
- Aging,
- Voltage surges,
- Chemical effects,
- Installation errors,
- Customer errors,
- Manufacturing defects.
