Last Updated on October 24, 2022 by Jose Villegas Jr.
Naturally, power cables are intended to be installed or buried underground. The quality of cable joints, branch connections, and good cable laying are all important factors that affect how reliable an underground cable network is.
Underground power cable laying can be done using one of three major techniques: direct laying, draw-in systems, or solid systems. The benefits and limitations of these three approaches are described below.
Direct Underground Power Cable Laying
Due to its ease of use and low cost, this method is the most popular. In order to protect the wires being installed using this approach against corrosion and electrolysis, bituminized paper and hessian tape must be used.
Laying Technique
- There is a trench that is 45 cm wide and 1.5 meters deep.
- The trench is then covered with a fine sand layer that is 10 cm thick.
- Over the sand bed, the cable is laid. The cable is shielded from ground moisture by the sand bed.
- The cable is then once more covered with a roughly 10-cm-thick layer of sand.
- To lessen the impact of mutual heating, a horizontal or vertical gap of roughly 30 cm is established when many cables are to be put in the same trench. The distance between the wires also ensures that a defect on one cable won’t harm the cable next to it.
- To protect the cable from mechanical harm, the ditch is subsequently filled with soil and bricks.
Advantages
Easier and less expensive than the other two techniques
The heat produced by cables can quickly escape via the ground.
Disadvantages
An entirely new excavation must be done, which costs as much as the new installation, in order to install new cables in order to meet an increased load requirement.
It’s difficult to make changes to the cable network.
Higher maintenance costs.
It can be challenging to locate a defect.
In crowded locations, such as major cities, where excavation is too expensive, this technique cannot be used.
Draw-in Method
With this technique, manholes are strategically placed along the cable route along underground cast iron or concrete pipelines or ducts. The cables are then drawn from the manholes and placed within the pipes. The three cable ducts are typically joined by a fourth pipe or duct that carries the pilot wires and relay protection connections. The distances between the manholes would need to make it simpler to draw the cables in. The radius of the corners must be larger at intersections or while changing lanes. In order to protect them when being pulled, the cables that are to be laid in this method must be served with hessian and jute rather than being armored.
Advantages
Manholes make it simple to make changes, expansions, or repairs to the cable network without having to re-excavate the ground.
The cable jointing process is made easier in this manner because the cables do not need to be armored.
The price of maintenance is very low.
fewer odds of a breakdown occurring because of the system’s excellent mechanical protection.
Disadvantages
The upfront expense is rather substantial.
The cables’ current carrying capability is decreased as a result of unfavorable heat dissipation circumstances.
Strong System
The cable is inserted using this technique into troughs made of cast iron, stoneware, asphalt, or treated wood. The troughing is filled with a bituminous or asphaltic compound and then covered once the cable is in place. Cables that are placed in this way could simply be covered in the lead because the troughing offers adequate mechanical security.
Because it is more expensive, involves expert labor, and requires favorable weather, this method is relatively infrequently employed nowadays.
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