The Importance of Soil and Backfilling for Underground Cables

June 29, 2020

One of the main sources of power for most appliances and equipment today comes from electricity. For decades, electricity has been distributed to every home and establishment through distribution lines, mainly through cables. These cables are typically installed on either tall poles or underground.

Cables that are placed on tall poles or towers are known as overhead cables. This type of cables is utilised by electrical companies since it provides high power and long-distance transmissions. Installation, maintenance, and repairs of these cables are also easy. However, these cables are so much vulnerable to extreme environmental conditions like lightning strikes, strong wind, heavy rain or snow, and so on.

The Rise of Underground Cables

Given the downside of overhead cables, some cities around the world are now starting to embrace underground cables. As the name implies, underground cables are cables that are located underground or underwater. Compared to overhead cables, underground transmission systems are much safer from any severe environmental and weather conditions. Additionally, they have lower transmission losses and can absorb more emergency power loads than overhead cables.

Of course, underground cables also have their own set of weaknesses. The installation of underground cables varies depending on the location and its geographic situation. Their installation and maintenance costs are also high since different sets of excavation works are required for them to be placed and repaired effectively and efficiently. High voltage transmission is also difficult with underground cables.

The Purpose of Soil and Backfilling

To minimise costly repairs, underground cables must be installed correctly right from the start of their operations. The problem with most underground cable installation is that contractors tend to select and install incompatible thermal backfill materials. Without great thermal backfill materials, the heat generated from the underground cables can easily dry out their surrounding soil. The soil will then act as an insulating blanket for the cables, which can ultimately damage the cables.

Proper selection of these materials allows underground cables to avoid failure even without regular maintenance and repairs. You see, underground cables generate heat whenever they are supplying power to households. This specific heat must then be dissipated and scattered through the surrounding for the cables to stay cool and avoid getting damaged.

With the use of correct thermal backfill rho, any thermal instability issues and heat flux can be easily managed by the native soil once the cables start to operate. As for the cables, any enhancements over the quality of the cable’s external thermal environment and soil can also increase their cable ampacity for up to 30%. All these benefits are only possible if you accurately measure the thermal properties of the native soil and use appropriate corrective thermal backfills.

Underground cables must utilise proper soil and backfilling to make them work fully. If you want to know more about soil and backfilling for underground cables, just contact us at Metro Pits. We have installed underground electrical conduits throughout Melbourne. This process requires VEDN accreditation and the installation of conduits for Low Voltage (LV) and High Voltage (HV) cables including feeds to substations.

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