A section view of a substation is a cut-away drawing that reveals a vertical slice through the substation
at a specific location. This view provides a detailed look at the arrangement of equipment within the
substation, including their relative heights and depths. Section views are crucial for understanding the
spatial relationships between various substation components and how they interact within the three-
dimensional space.
Figure 35: Section View of a Substation
Both the Layout plan and section should be designed in accordance with relevant standards and guide-
lines, such as the IEEE 80 for substation grounding and IEEE 998 for lighting protection They should
also consider safety requirements and the need for ease of operation and maintenance.
4.2.3 Earthing
Earthing, also sometimes referred to as grounding, is a crucial element in substation safety and func-
tionality. It involves creating a low-resistance path for electrical current to flow back to the earth in the
event of a fault or surge. This helps achieve two main goals:
• Safety: By providing a clear path for fault currents, earthing minimizes the risk of electric shock
to personnel working within the substation.
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• Equipment protection: A proper earthing system safeguards substation equipment from damage
caused by excessive fault currents.
The IEEE 80 standard, titled "Guide for Safety in AC Substation Grounding," provides valuable recom-
mendations for designing, installing, testing, and maintaining earthing systems in AC substations.
Parameters considered for earthing of substation
• Ground Potential Rise: Ground Potential Rise (GPR) can be defined as the product of ground
electrode impedance with respect to zero-earth and the current flowing through that electrode
impedance. GPR = 10 × Rg: GPR can be controlled by keeping resistance of the earthing grid as
low as possible, so that the earth fault conditions are limited for maintaining the step and touch
the potential limits. Step potential, mesh potential, and transferred potential plays a vital role in
the calculation of an earthing system and to ensure equipment safety as well as human safety.
• Step potential: The potential difference between two points on the surface of the earth separated
by one pace that is normally assumed to be one meter in the direction of the maximum potential
gradient is known as ‘Step Potential’. Considering a constant body impedance of 1000Ω Step
potential can be calculated as
Where, ρs – resistivity of the surface layer, ∁s – scaling factor due to the protective surface layer
and ts – Time in seconds.
• Touch potential: The potential difference between a grounded metallic structure and a point on
the earth’s surface at a distance equal to the normal maximum horizontal reach is approximately
one meter.
Where, ρs – resistivity of the surface layer ∁s – scaling factor due to the protective surface layer
and ts – Time in seconds.
• Transferred voltage: It is a special case of touch potential where the voltage generated is trans-
ferred to/from an external point to the substation.
• Mesh potential: Mesh potential is the maximum touch voltage generated within a mesh of an
earth grid. The mesh potential is defined as the product of the soil resistivity (ρ), the configuration
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