Importance of Earth Grid Design

Importance of Earth Grid Design

Importance of Earth Grid Design

 

An earthing grid is used as an electrical component, connected to the earth at zero potential. When a fault condition occurs, the high energy dissipates into the ground through a low-impedance path. The earth grid design system should involve mitigating the hazards arising from step, touch potentials, and bringing down the earth’s resistance.

These problematic issues can be easily eliminated by equipping an earthing grid that should be appropriately designed to minimize the harmful effect.

Problem Statement

To redesign an earth grid for a 765kV substation, as the cost of implementing the proposed earth grid design was exceeding the budget. As a renewable energy project, it created a unique challenge of grid stability and sub-synchronous resonance, at the point of coupling, compared to traditional energy transmission projects.

 Approach
The grid was re-designed and optimized using CDEG software and by enveloping the ground conductors with our OEM earth enhancement compounds Curec+® and Curecon® which perform as per IEEE 80 Clause 14.5 d & 14.5 b respectively.
At the time of fault or lightning, the current interaction capacity (A/m) of Curec+ and Curecon with earth grid conductor is approximately 6 and 1.5 times higher than electrical grade bentonite respectively. This enables to achieve low earth grid resistance and maintains grid potential within permissible limits along with a significant reduction in the buried length of grid conductors. Over and above, these products provide permanency to earthing systems.

Design Result
Description Client Design Optimized Design
Grid spacing (m) 20/30 >40
Total length of conductor Lc (m) 14012 11560
Number of earth rods 3m long 260 149

The earth grid optimization leads to overall cost savings of 20% along with reduced trench length leading to saving of time and labor costs. This optimization ensured that the dangerous potentials were kept less than the tolerable values. The below table provides the cost comparison of the unoptimized design provided by the client and Manav Energy optimized design.

Description Client
(In Lakhs)
Optimized
(In Lakhs)
40-mm MS conductor cost 69 57
Earth rods cost 4 2.2
Trenching/Backfilling of conductor 42 35
Earth pit installation cost 6 3
Total cost 121 97.2
Savings in Cost 23.8 lacs
Saving on Optimized design 20%

  Benefits

  • Reduced BOQ (conductor length)
  • Reduced Project Cost (reduction in trench length, welding joints, labor cost, installation time).
  • Achieve the least seasonal variation of grid resistance due to the use of organic earth-enhancing compounds Curec+® and Curecon® conforming to IEEE 80 Clause 14.5 (d) & 14.5 (b) respectively
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