Mesh Grounding Design for GIS: Importance, Standards, and Analysis Tools

1. Introduction

Grounding systems in high-voltage substations—especially Gas Insulated Substations (GIS)—play a critical role in ensuring operational safety, equipment protection, and electromagnetic compatibility. Among the grounding approaches, mesh grounding is the most widely adopted due to its effectiveness in dissipating fault currents and limiting hazardous potentials.

This article explores the importance of mesh grounding in GIS, the relevant standards, the software tools used for analysis, and recommended mesh sizing practices, with a case example for a 33 kV, 65 kA substation.

2. Importance of Mesh Grounding in GIS

A GIS operates at high voltages in a compact metal enclosure, which increases the need for a robust and reliable grounding system. A mesh grounding grid ensures:

• Personnel Safety. Proper grounding minimizes touch and step voltages, significantly reducing the risk of electric shock during fault conditions or switching surges.
• Fault Current Dissipation. A well-designed mesh grid provides a low-impedance path for high fault currents—such as from lightning strikes or equipment failures—safely dispersing energy into the ground.
• Equipment Protection. Effective grounding reduces ground potential rise (GPR) and transient overvoltages that can damage control electronics and insulation systems.
• Electromagnetic Compatibility (EMC). A continuous and bonded grounding grid suppresses electromagnetic interference (EMI) and provides a stable reference for protection and control systems.
• Lightning and Surge Mitigation. Mesh grounding, integrated with the lightning protection system, helps to safely discharge induced or direct lightning currents.

3. Standards Governing Mesh Grounding

A variety of international standards and guidelines prescribe the design, performance, and testing of substation grounding systems:

Standard	Description
IEEE 80	Guide for AC Substation Grounding. Defines touch/step voltage limits and design methods.
IEC 61936-1	Specifies requirements for power installations >1 kV AC, including grounding.
IEEE 837	Standard for qualifying permanent grounding connections.
IEEE 1050	Guide for instrumentation/control grounding in high-voltage environments.
IEC 62305	Covers bonding and grounding for lightning protection.
CIGRÉ Technical Brochures	Offer case studies and advanced design recommendations for complex GIS grounding.

3. Recommended Mesh Grid Size – Case of a 33 kV, 65 kA Substation

The design of the grounding mesh depends on several key factors including fault level, soil resistivity, fault clearing time, and safety criteria. For a 33 kV substation with a 65 kA fault level, the recommended mesh grid size is:

3.1 Mesh Grid Size: 3 m × 3 m to 5 m × 5 m

• 3 m mesh spacing is recommended in high-resistivity soils (>100 Ω·m) or in sensitive areas.

• 5 m mesh spacing may be acceptable for lower resistivity soils and non-critical zones.

3.2 Design Considerations

• Burial Depth: 0.5 to 0.8 m.

• Surface Treatment: Crushed rock layer with high resistivity (~3000 Ω·cm) to reduce step voltage risk.

• Ground Rods: Installed at mesh intersections and perimeter for lowering grid resistance.

3.4 Safety Calculation (IEEE 80)

Touch voltage limits can be calculated as:

Where:>

• $\rho$ = soil resistivity (Ω·m)

• tft_ftf​ = fault duration (s)

This ensures that designed mesh spacing maintains voltage levels within IEEE-recommended limits.

4. Software Tools for Grounding Analysis

Accurate modeling of grounding systems requires simulation tools that support fault current analysis, soil modeling, and compliance checks. Below are the most widely used software tools:

CDEGS remains the industry benchmark for large-scale GIS installations due to its accuracy and compliance support.

Conclusion

Mesh grounding is an essential component of GIS safety and reliability. For medium voltage substations with high fault currents—like a 33 kV, 65 kA installation—designers must ensure that the mesh spacing, soil treatment, and conductor layout all work together to control dangerous potentials during faults. Adherence to IEEE and IEC standards, combined with robust simulation using tools like CDEGS or ETAP, ensures a grounding system that meets safety and performance requirements.