Grounding in electrical substations of high and medium voltage is the most fundamental protection system of any electrical installation: if it fails, people die. Its design determines the step and touch voltages an operator will experience during a ground fault, and it must ensure these values remain below the safety thresholds defined by the IEEE 80-2013 standard and the RPTD No. 06 pliego from the SEC.
In Chile, where substations operate in high-resistivity desert, mountain terrain above 4,000 masl, and saline coastlines, the design of grounding in electrical substations does not allow generic solutions: each project requires a soil resistivity study, soil modeling, and an optimized design that balances safety, cost, and constructability.
If your project is in the engineering phase and you need to validate that the grounding in electrical substations design complies with the safety criteria against the updated short-circuit currents of the SEN, this guide covers the complete process: from resistivity measurement to the verification of step and touch voltages, including the challenges imposed by Chilean geography.
What is grounding in electrical substations and why is it critical?
Grounding in electrical substations consists of a system of buried conductors —typically a copper grid— that connects all the metallic parts of the installation (structures, equipment enclosures, perimeter fences) to earth. Its purpose is threefold:
- Protect human life by limiting step and touch voltages during a ground fault.
- Protect equipment by providing a low-impedance path for the fault current.
- Ensure the correct operation of protection systems, which depend on a stable earth reference to detect faults.
When a ground short-circuit occurs, the fault current flows through the grid and raises the potential of the ground around the installation. This phenomenon, known as GPR (Ground Potential Rise), is what generates dangerous voltages. The design of grounding in electrical substations seeks to ensure that, even under the worst expected fault, the step and touch voltages do not exceed the limits a human being can withstand without risk of electrocution (IEEE, 2013).
Design methodology according to IEEE 80-2013: step by step
The IEEE 80-2013 (Guide for Safety in AC Substation Grounding) standard is the international reference for the design of grounding in electrical substations. The SEC expressly recognizes it in RPTD No. 06, and the Coordinador Eléctrico Nacional requires it in its technical design specifications. The process is summarized in the following steps:
| Step | Action | Technical detail |
|---|---|---|
| 1 | Soil resistivity measurement | Wenner method (4 equally spaced electrodes). A resistivity profile is obtained at different depths. |
| 2 | Soil modeling | 2-layer model (minimum per IEEE 80). CDEGS, ETAP or similar software. |
| 3 | Conductor sizing | Minimum copper conductor cross-section based on maximum fault current and clearing time. |
| 4 | Calculation of tolerable voltages | Maximum step and touch voltages based on body weight (50 kg / 70 kg), surface resistivity and fault time. |
| 5 | Preliminary grid design | Grid geometry, burial depth (0.5–1.0 m), spacing between conductors. |
| 6 | Calculation of ground resistance (Rg) | Must comply with Rg ≤ 5 Ω for transmission substations. In mining, Rg ≤ 1 Ω is frequently required. |
| 7 | GPR calculation | GPR = IG × Rg. If GPR < tolerable touch voltage, the design is safe without further calculations. |
| 8 | Detailed calculation of mesh and step voltages | Km, Ks, Ki factors. Verification against tolerable thresholds. If it does not comply, the design is iterated. |
| 9 | Optimization and iteration | Area increase, addition of perimeter rods, spacing reduction, high-resistivity surface material. |
| 10 | Post-construction verification (IEEE 81) | On-site ground resistance measurement. Fall-of-potential method. |
This process is iterative: if the calculated voltages exceed the tolerable limits, the engineer must adjust the grid geometry until finding a configuration that complies. In high-resistivity soils —such as those found in the Chilean mountains— the design of grounding in electrical substations may require large-extension grids, deep rods, or chemical soil treatment (IEEE PCIC, 2022).
Soil resistivity measurement: the starting point
No design of grounding in electrical substations can begin without real soil resistivity data. Resistivity varies enormously depending on soil type, moisture, temperature, and geological stratification. In Chile, the typical ranges are:
| Soil type | Typical resistivity (Ω·m) | Typical location in Chile |
|---|---|---|
| Wet clay | 10 – 100 | Central valleys, southern zone |
| Silt, agricultural soil | 50 – 200 | O’Higgins to Los Lagos regions |
| Dry sand | 200 – 2,000 | Northern coast, Atacama desert |
| Gravel, rocky soil | 1,000 – 5,000 | Foothills, high-altitude mining sites |
| Solid rock / permafrost | 5,000 – 50,000+ | Mountains above 4,000 masl, glacier zones |
The Schlumberger 4-electrode method is widely used for measuring soil resistivity. It consists of installing four aligned electrodes, injecting current through the two outer electrodes and measuring the potential difference between the two inner electrodes, which remain close to the center of the array. By progressively increasing the separation of the current electrodes, it is possible to obtain apparent resistivity values at different depths, which allows modeling the soil in layers (Zohdy, Eaton & Mabey, 1974).
It is essential not to reuse resistivity data from previous projects in the same geographic area. Resistivity can vary drastically within a few meters, and using data that is not representative of the site is one of the most frequent causes of deficiencies in grounding in electrical substations (IEEE PCIC, 2022).
Challenges of designing grounding in electrical substations in Chile
Chile’s geography and climate impose unique conditions on the design of grounding in electrical substations that are not found in most international reference texts.
High resistivity in mountain mining sites
Large-scale mining substations in northern Chile are frequently located above 3,000–4,500 masl, in rocky soils with resistivities that can exceed 5,000 Ω·m. Under these conditions, achieving a grid resistance below 5 Ω —a basic requirement for grounding in electrical substations of transmission— requires aggressive strategies: large-extension grids, deep rods drilled into rock, grounding electrodes embedded in concrete (Ufer electrodes), or chemical soil treatment with low-resistivity compounds (IEEE PCIC, 2022). Learn more about the electrical engineering for mining projects we have developed under these conditions.
Seismicity and mechanical connections
Chile is one of the most seismic countries in the world. The connections between the ground grid and the equipment downleads must withstand the differential displacements produced by an earthquake without losing electrical continuity. This requires the use of flexible connectors and a design that contemplates ground deformations according to NCh2369:2023. Correct grounding in electrical substations located in seismic zones depends as much on the electrical design as on coordination with civil-structural engineering.
Corrosion in saline and desert environments
Coastal and desert substations face highly corrosive environments. The copper conductor must be sized with additional margin to compensate for cross-section loss due to corrosion throughout the installation’s service life (40–50 years). Welded connections (exothermic Cadweld-type welding) are preferred over bolted ones in these environments, guaranteeing the integrity of grounding in electrical substations throughout its operational life.
Expansion of existing substations
When an operating substation is expanded, the existing grounding in electrical substations must be verified to confirm that the grid is compatible with the new short-circuit currents. The Coordinador Eléctrico Nacional has carried out diagnostics of the SEN grids, evaluating their capacity to receive expansion works. Frequently, the expansion requires extending the existing grid and recalculating step and touch voltages with the new fault levels. For more detail, see our article on expansion of electrical substations.
Substations in renewable parks
Step-up substations for solar and wind parks are located in terrain where resistivity can be extremely variable. In addition, the presence of the park’s medium-voltage collector network generates interference with the ground grid that must be properly modeled when designing grounding in electrical substations for step-up applications. Review our electrical engineering projects to see cases in renewable parks.
Applicable international standards
The Chilean regulatory framework for grounding in electrical substations (RPTD No. 06, Technical Annex CNE) is aligned with international standards. For details on SEC regulations, see our article on expansion of electrical substations.
| Standard | Scope | Key application |
|---|---|---|
| IEEE 80-2013 | Guide for safety in AC substation grounding | Grid design, step/touch voltages, GPR |
| IEEE 81-2012 | Guide for measuring resistivity, impedance and earth potentials | Wenner method, post-construction Rg measurement |
| IEEE 837-2014 | Qualification of permanent connections for substation grounding | Exothermic welding, compression connectors |
| IEEE 367-2012 | Practice for determining the maximum ground potential of substations | GPR calculation for telecommunications coordination |
| IEC 61936-1 | Electrical installations above 1 kV AC: common rules | General grounding requirements for HV |
| IEC 62305 | Protection against lightning strikes | Coordination with lightning protection system |
| EN 50522 | Earthing of AC power installations above 1 kV | European standard, reference for projects with European technology |
| CIGRÉ TB 749 (2018) | Modernization of grounding systems in existing substations | Diagnosis and renovation of grids in old substations |
One aspect that deserves special attention is ground grid optimization. Studies published in Scientific Reports (Nature, 2024) and PLOS ONE (Permal et al., 2021) demonstrate that applying optimization algorithms (Simulated Annealing, genetic algorithms) to the design of grounding in electrical substations can reduce the amount of conductor required by up to 57% without compromising safety.
Software for the design of grounding in electrical substations
Modern design of grounding in electrical substations relies on specialized software that allows modeling multilayer soils, complex geometries, and calculating potential distributions in 3D:
CDEGS (SES Technologies): The most widely used suite worldwide. It includes the MALT (grid calculation), RESAP (multilayer soil modeling) and HIFREQ (high-frequency analysis) modules. It is the reference software of the Coordinador Eléctrico Nacional for SEN grid diagnostics.
ETAP Ground Grid: Module integrated into the ETAP platform, it allows IEEE 80-compliant design with a graphical interface and direct linkage to the system’s short-circuit studies.
AutoGrid Pro (ESGRID): Specialized in the design and optimization of grounding in electrical substations, with 3D modeling and multilayer soil capability.
MATLAB (custom scripts): Used in research to implement optimization algorithms over IEEE 80 models.
Regardless of the software used, the result must be verified on-site through resistance measurements according to IEEE 81, completing the design–construction–verification cycle.
Post-construction verification according to IEEE 81
The design of grounding in electrical substations does not end with the drawings. On-site verification is mandatory and must be carried out at two moments:
- After the construction of the grid, before energization: the ground resistance is measured using the fall-of-potential method and compared with the calculated value.
- Periodically during the service life: to verify that corrosion, changes in soil moisture, or expansions have not degraded the grid’s performance.
The NETA World Journal (2024) indicates that the typical target for transmission substations is a ground resistance of 1.5 Ω or less relative to remote earth. For distribution substations, values of up to 5 Ω are acceptable according to IEEE 80.
International benchmarks in grounding in electrical substations
CFETR Substation (China, 2024): Researchers designed the ground grid of the CFETR experimental fusion reactor applying IEEE 80 with 3D modeling in CDEGS. The design was validated through simulation, obtaining a difference of less than 1% between calculated and simulated values for step and touch voltages (Scientific Reports, 2024).
Substations in solid rock (Canada): In mining installations in the Canadian Shield, where resistivity exceeds 10,000 Ω·m, Ufer electrodes have been successfully implemented as a complement to conventional grids, reducing ground resistance by up to 60% (IEEE PCIC, 2022).
PacifiCorp substations (USA): PacifiCorp specifications require peripheral conductor both inside and outside the perimeter fence, ground rods at each fence post, and connection of all foundation reinforcement to the main grid, maximizing the use of Ufer electrodes (PacifiCorp, 2016).
SEN grid diagnostics (Chile, 2019): The Coordinador Eléctrico Nacional carried out a diagnostic study of grounding in electrical substations of the SEN, modeling with CDEGS and evaluating the capacity of each grid to withstand the foreseen expansion scenarios. The study revealed that several substations required grid extension to meet safety criteria against the increase in fault currents (CEN, 2019).
The role of design engineering
The design of grounding in electrical substations is a specialized discipline that requires simultaneous mastery of electrical engineering, geotechnics, and regulations. The design engineering firm contributes:
- Coordination of the on-site resistivity measurement campaign.
- Soil modeling and design of the ground grid for grounding in electrical substations in accordance with IEEE 80, using specialized software (CDEGS, ETAP).
- Verification of step and touch voltages under the updated short-circuit currents of the SEN.
- Design of equipment downleads and grid connections, including exothermic welding and connector specifications.
- Coordination with civil-structural design to integrate Ufer electrodes into foundations.
- Supervision of grid construction and post-construction verification according to IEEE 81.
In ITO (Technical Site Inspection) projects in substations, the verification of grounding in electrical substations is one of the critical milestones before authorizing energization.
Frequently asked questions about grounding in electrical substations
What standard is used for the design of grounding in electrical substations?
The international reference is the IEEE 80-2013 standard (Guide for Safety in AC Substation Grounding). In Chile, the SEC’s RPTD No. 06 pliego recognizes it as a design standard, and the Coordinador Eléctrico Nacional requires it in its technical specifications for SEN installations.
What is step voltage and touch voltage?
Step voltage is the potential difference between the two feet of a person walking during a ground fault. Touch voltage is the difference between an energized metallic structure that the person touches and their feet. Both must remain below thresholds defined by IEEE 80 to prevent electrocution. For more context, see our article on expansion of electrical substations.
What is the acceptable ground resistance for an electrical substation?
IEEE 80 does not define a single value, as it depends on the fault current, the clearing time, and the grid area. As a reference, SEN transmission substations typically seek values of 1.5 Ω or less. The definitive safety criterion is the step and touch voltages, not the resistance itself.
How is soil resistivity measured to design the ground grid for grounding in electrical substations?
The Wenner 4-electrode method (IEEE 81) is used. Four equally spaced electrodes are driven in a straight line, current is injected between the two outer ones and the voltage is measured between the inner ones. By varying the distance between electrodes, a resistivity profile is obtained at different depths (NETA World, 2024).
What to do when the soil has very high resistivity?
Techniques are applied such as: increasing the grid area, installing deep rods drilled into rock, using Ufer electrodes embedded in concrete foundations, applying high-resistivity surface material (crushed gravel) to raise the tolerable voltages, and in extreme cases, chemical soil treatment. IEEE PCIC (2022) demonstrates that it is possible to design safe grounding in electrical substations systems even with high resistance to remote earth. These challenges are especially frequent in the electrical engineering projects for mining that we develop at altitude.
How is the ground grid for grounding in electrical substations integrated with lightning protection?
The lightning protection system (IEC 62305, IEEE 998) must be connected to the main ground grid of the substation. The lightning arrester downleads are connected directly to the grid, ensuring that the lightning current is dissipated safely without generating dangerous overvoltages in the equipment.
Does your project need a grounding in electrical substations design that complies with IEEE 80?
The design of grounding in electrical substations is one of the most critical —and most underestimated— aspects of a substation project. A design error is not detected until a fault occurs, and at that moment the consequences can be fatal. With more than 20 years designing substations for mining, energy, and transmission in Chile, Esinel Ingenieros has the experience and tools to deliver a ground grid design that complies with IEEE 80, RPTD No. 06, and the requirements of the Coordinador Eléctrico Nacional.
Let’s validate your grounding design together. → Schedule a technical meeting
References
Cai, L. et al. (2024). Design of substation grounding grid in CFETR. Scientific Reports, 14, 24879. https://www.nature.com/articles/s41598-024-76764-5
Coordinador Eléctrico Nacional. (2019). Diagnostic study of common installations — Annex 2: Ground grids. CEN. https://www.coordinador.cl/
Coordinador Eléctrico Nacional. (2019). Technical design specification for AIS substations (COOR-DID-SE-TEC-ET-DIS-AIS). CEN. https://www.coordinador.cl/
IEEE. (2013). IEEE Std 80-2013: Guide for Safety in AC Substation Grounding. IEEE Standards Association.
IEEE. (2012). IEEE Std 81-2012: Guide for Measuring Earth Resistivity, Ground Impedance, and Earth Surface Potentials of a Grounding System. IEEE Standards Association.
IEEE PCIC. (2022). Designing Safe and Reliable Grounding in AC Substations with Poor Soil Resistivity. IEEE Petroleum and Chemical Industry Conference.
Permal, N. et al. (2021). Optimization of substation grounding grid design for multilayer soil using Simulated Annealing. PLOS ONE, 16(8). https://doi.org/10.1371/journal.pone.0256298
SEC. (2020). Technical Regulatory Pliego RPTD No. 06: Grounding. Superintendencia de Electricidad y Combustibles. https://www.sec.cl/
Zohdy, A. A. R., Eaton, G. P., & Mabey, D. R. (1974). Application of surface geophysics to ground-water investigations (Techniques of Water-Resources Investigations, Book 2, Chapter D1). U.S. Geological Survey. https://doi.org/10.3133/twri02D1