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Substation Roads
- Thread starter SKJ25POL
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Interior access road in the substation is usually a crushed rock and occasionally installed with bituminous materials. For larger substations, the access road may consist of an excavating fill with aggregate base course and surfacing material for the entire yard and 3 t0 5 ft beyond the fence. The following should apply:
Excavated subbase: Typically install 6” of Coarse Stone often added crushed stone dust forming an Aggregate similar to ASHTO 3A
Final grade: Surfacing material 4 to 6 inches of crushed stone or rock cover the entire substation yard per IEEE Std 80.
Highway standard AASHTO or DOT standards apply typically spec. for Class H20 loadings. Also
The turning radii are also observed with a complete environmentally approved plan.
Excavated subbase: Typically install 6” of Coarse Stone often added crushed stone dust forming an Aggregate similar to ASHTO 3A
Final grade: Surfacing material 4 to 6 inches of crushed stone or rock cover the entire substation yard per IEEE Std 80.
Highway standard AASHTO or DOT standards apply typically spec. for Class H20 loadings. Also
The turning radii are also observed with a complete environmentally approved plan.
bacon4life
Electrical
Any fines or dust reduces the resistivity of the rock layer. Unfortunately, many kinds of crushed rock are impossible to drive across unless there fines included to lock everything in place.
In my area, the local gravel pit offers something call fractured railroad ballast. Apparently there are several ways to break rocks into smaller pieces, and this pit's fractured rock uses a different method than typical crushed rock. The fractured rock has fairly large, angled surfaces, so it ends up locking in place moderately well. Regular crushed rock in my region tends to be uniformish, roundish balls.
Since rock is a very regional thing, hopefully your local utility has done resistivity and drive-ability testing for your locally available materials.
In my area, the local gravel pit offers something call fractured railroad ballast. Apparently there are several ways to break rocks into smaller pieces, and this pit's fractured rock uses a different method than typical crushed rock. The fractured rock has fairly large, angled surfaces, so it ends up locking in place moderately well. Regular crushed rock in my region tends to be uniformish, roundish balls.
Since rock is a very regional thing, hopefully your local utility has done resistivity and drive-ability testing for your locally available materials.
It is correct what bacon4life points it out.
A common way to address the fine issue is consider the extra layer of compacted crushed rock used in the subsurface of the access road and add the resistance of the surfacing material with the appropriate derated resistivity due to the fines.
It is a common practice to increase the thickness of the surfacing material to account for the fine migration during the lifetime of the substation, usually 30 years or so. Another approach is monitoring the safety integrity of the substation by periodic tests measuring the step and touch potentials.
A common way to address the fine issue is consider the extra layer of compacted crushed rock used in the subsurface of the access road and add the resistance of the surfacing material with the appropriate derated resistivity due to the fines.
It is a common practice to increase the thickness of the surfacing material to account for the fine migration during the lifetime of the substation, usually 30 years or so. Another approach is monitoring the safety integrity of the substation by periodic tests measuring the step and touch potentials.
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