Title: Research report on which is best practice to use for cable trenches fill
between sand and furnace slag.
Sand is often used in cable trenches to provide a bedding material that is free of
rocks and ensures good thermal conductivity.
In hazardous areas, such as those with oil which leads back to our inverters, filling
cable trenches with sand is common practice. This is done to prevent the passage
of hydrocarbons and restrict the spread of fire.
Sand and furnace slag are both used as bedding materials in cable trenches, each
with its own advantages.
Sand is commonly used due to the following several benefits:
1. Protection: It provides a bedding material free of rocks, protecting the
cables from potential damage during installation.
2. Thermal Conductivity: It ensures good thermal conductivity, crucial for
high voltage cables as it helps dissipate the heat generated by the cables.
3. Preventing Fire Spread: In hazardous areas, such as oil and gas
installations, sand fill in cable trenches can prevent or restrict the passage
of hydrocarbons and the spread of fire.
4. Avoiding Moisture: It protects the cable from moisture from the ground.
5. Preventing Trapping of Hazardous Material: Filling cable trenches with
sand leaves no space for hydrocarbon to get trapped in the trench, which
could otherwise be a hazard.
On the other hand, furnace slag has its own advantages:
6. Durability: Slag is a byproduct of metal smelting, and its durability can
provide long-lasting protection for cables.
7. Cost-Effectiveness: In some regions, slag may be more readily available
and cost-effective than sand.
8. The use of furnace slag in industrial practices is gaining attention due to its
potential benefits. For instance, Electric Arc Furnace (EAF) slag has been
considered for use as a supplementary cementitious material. However, its
use in cable trenching is not commonly reported
The electrical properties of furnace slag are not well-documented. However, its
physicochemical properties have been studied, and it’s known that the
composition and properties of slag can be highly variable. This variability could
potentially affect its suitability for use in cable trenching.
The other findings depend on the composition of the slag we have at hand as
regarding the electrical conductivity of furnace slag, studies have shown that the
electrical conductivity of high aluminum blast furnace slags decreases as the
content of Al2O3 increases. This is because Al3+ has a strong preference to form
AlO4 5+ tetrahedron and incorporates into the network of SiO4 4+ which enhances
the degree of polymerization of melts. However, the electrical conductivity
increases with gradually increasing the CaO/SiO2 ratio, owing to the increase of
concentration of Ca2+ ion which acts as the charge carrier and the decreases of
degree of polymerization.
In conclusion, the choice between sand and furnace slag often depends on the
specific requirements of the project, local regulations, and availability of materials.
However, from my findings sand is a better industrial practice.
International Standards:
The IEEE 525-2007 provides guidelines for the design and installation of cable
systems in substations.
The IEC 60287 series covers the current-carrying capacity of cables under steadystate conditions, and IEC 60853 covers cyclic conditions.
REFERENCES
1.
Assessment of Physicochemical Properties of Electrical Arc Furnace Slag ...
2.
IEEE Guide for the Design and Installation of Cable Systems in Substations
3.
Slag properties and design issues pertinent to matte smelting electric ...
4.
Underground Cable Laying All You Need to Know - STL Tech
5.
Electrical Conductivities of High Aluminum Blast Furnace Slags - J-STAGE