Earthing Grids Explained: Safeguard Your Electrical System

Have you ever wondered what keeps our electrical systems stable and people safe from electrical hazards? The answer lies beneath our feet, intertwined with the soil in the form of an earthing grid. This intricate network, also known as a grounding grid, is designed to disperse electrical currents into the ground, serving as a critical component in the protection and efficiency of our electrical infrastructure. Earthing grids safeguard everything from residential properties to vast industrial complexes, ensuring that in the event of a fault, the current is safely redirected away from equipment and, most importantly, people.

An earthing grid is a network of interconnected conductors buried underground. The primary purpose of an earthing grid is to provide a low-resistance path for fault currents to flow to the earth. They protect electrical systems, infrastructure, and human safety in several ways:

• Electrical System Protection: They dissipate fault currents, preventing dangerous voltage buildups that could damage equipment or cause fires.
• Infrastructure Protection: They direct fault currents to the earth, reducing the risk of damage to nearby structures and utilities.
• Human Safety: They limit the voltage gradients in the surrounding area, reducing the risk of electrical shock to people.

Earthing grids consist of several key components:

• Earthing Conductors: These are typically made of copper or copper-clad steel. They are buried in trenches and interconnected to form a grid pattern.
• Grounding System Design: This includes the layout of the grid, the size and spacing of conductors, and the selection of appropriate electrodes.
• Earthing Grid Materials: The materials used for earthing grids must have high conductivity and be resistant to corrosion. Copper is a popular choice due to its superior conductivity and corrosion resistance.

Ensuring the proper functioning of an earthing grid requires in-depth understanding of the earth’s contribution to the system. The earth itself plays an integral role in dispersing fault currents, acting as a return path to complete an electrical circuit. It is this crucial role that underpins the safety mechanisms which protect both equipment and human life.

Soil resistivity is a key factor that impacts the effectiveness of earthing grids. A low soil resistivity indicates a higher conductivity, which facilitates the easy passage of fault currents back into the ground, ensuring electrical safety and reducing the risk of electrical hazards. Conversely, a high soil resistivity could compromise the grid’s efficiency and safety.

Therefore, professionals utilize soil resistivity measurements to tailor the earthing grid design for optimum safety and performance. Such assessments help determine the depth and spacing of electrodes necessary to achieve an effective earthing system.

In Australia, there are established techniques for measuring soil resistivity, such as:

• The Wenner Alpha Four-Pin Method, which involves placing four equally spaced probes into the soil and measuring the resistance between them.
• Schlumberger Method, suitable for deeper soil measurements and often employed when designing earthing systems for larger installations.

Both methods require careful consideration of the local geological conditions, climate, and the specific requirements of the earthing grid. Furthermore, taking multiple measurements throughout the year can account for seasonal variations in soil moisture levels, ensuring a reliable and consistent design baseline for the earthing grid.

Through precise soil resistivity measurement and evaluation, professionals can ensure that the earthing grids deployed across various Australian terrains are effective, compliant, and suited to their environmental context. This meticulous approach safeguards our electrical infrastructure and the communities that rely on it.

Designing an effective earthing grid requires careful consideration of several key factors.

Soil resistivity is a crucial factor in earthing grid design. It determines how well the soil conducts electricity. Engineers perform soil resistivity tests to determine the soil’s conductivity. These tests are essential for accurate design calculations. The Wenner four-point method is a commonly used technique for measuring soil resistivity.

Fault currents are the high currents that flow during fault conditions, such as short circuits or lightning strikes. The fault current is a critical factor in earthing grid design. Engineers calculate the maximum fault current that the system could experience. This helps them determine the size and type of conductors needed to handle the current safely.

Selecting appropriate materials is crucial for a robust and long-lasting earthing grid. The most common materials include:

• Conductors: Copper is often the preferred material for earthing conductors because of its high conductivity and resistance to corrosion. Copper-clad steel is an alternative for applications where cost is a concern.
• Electrodes: Earth electrodes are typically made of copper or copper-clad steel rods. They can be driven into the ground or installed in boreholes.

The mesh size refers to the spacing between the conductors in the grid. The configuration refers to the overall pattern of the grid. Engineers determine the mesh size and configuration to balance effectiveness and cost. A denser mesh generally leads to lower resistance but can be more expensive.

The maximum grid area for Greenfield substations is limited to 150 square meters. This limitation is based on the typical design life of a substation, which is 50 years. For brownfield expansions, the grid area may be adjusted based on the existing infrastructure and the project’s requirements. The typical depth for the earth grid is 500mm below finish ground level, ensuring adequate burial depth and contact with the soil.

Earthing grid design must comply with relevant standards and regulations. In Australia, these standards include:

• AS 2067:2016, Substations and high voltage installations exceeding 1 kV a.c: This standard outlines the requirements for substations and high-voltage installations.
• IEEE 80-2000, IEEE Guide for Safety in AC Substation Grounding: This international standard provides guidance on safety in AC substation grounding.

Installing an earthing grid involves a systematic process that prioritizes safety:

1. Site Preparation: The area for the grid is cleared, and any existing utilities or underground infrastructure are located and marked.
2. Trench Excavation: Trenches are excavated to the required depth, typically between 0.3 and 0.5 meters.
3. Conductor Installation: Conductors are laid in the trenches, ensuring proper spacing and connections.
4. Electrode Installation: Electrodes are installed at strategic locations within the grid. They are connected to the conductors using appropriate methods, such as welding or compression connectors.
5. Backfill and Compaction: The trenches are backfilled with suitable material, such as crushed rock or a mixture of bentonite and gypsum. The backfill is compacted to ensure stability and good electrical contact.
6. Testing: Once the installation is complete, the grid undergoes thorough testing to confirm its effectiveness and ensure compliance with standards.

Safety is paramount during every stage of earthing grid design and installation. The most significant hazard is electric shock, which occurs if a fault current flows through the human body. This can happen if a person comes into contact with a conductor carrying fault current or if there are dangerous voltage gradients in the area surrounding the grid. Here are some general safety tips to follow:

• PPE: Workers must wear appropriate PPE, including insulated gloves, footwear, and clothing.
• Isolation: Always isolate electrical equipment before working near or on the grid.
• Insulated Tools: Use insulated tools and switch sticks to prevent contact with energized components.
• Voltage Gradients: Be mindful of potential voltage gradients near the grid and take appropriate precautions.

Regular testing is essential to ensure that an earthing grid remains effective and safe. Engineers employ various tests to evaluate the grid’s performance:

• Earth Resistance Measurement: This test measures the resistance between the earthing grid and the earth. It provides a direct assessment of the grid’s ability to conduct fault currents.
• Step and Touch Voltage Measurement: These tests measure potential voltage gradients that could exist around the grid. Step voltage is the voltage difference between a person’s feet when standing near the grid. Touch voltage is the voltage difference between a grounded structure and a person touching it.
• Ground Potential Rise (GPR) Calculations: GPR, or Earth Potential Rise, is the voltage difference between the earth grid and a remote earth. This calculation helps determine how far a hazardous voltage might extend.

Maintaining an earthing grid ensures its long-term effectiveness and safety. Regular maintenance practices include:

• Visual Inspections: Regular visual inspections are vital to identify any signs of corrosion, damage, or loose connections. This is usually performed above ground and can be combined with visual inspections of other substation components.
• Cleaning Connections: Connections between conductors and electrodes must be kept clean to maintain good electrical contact. Accumulated dirt or corrosion can increase resistance, reducing the grid’s effectiveness.
• Checking for Corrosion: Corrosion is a major concern for earthing grids, as it can lead to increased resistance and failure. Inspect conductors and electrodes for signs of corrosion and replace or repair them as needed.
• Repairing or Replacing Damaged Components: Any damaged conductors or electrodes should be repaired or replaced promptly to maintain the grid’s integrity.

Earthing grids are crucial for the safety and reliability of electrical systems. They protect equipment, infrastructure, and people from the dangers of electrical faults and surges. By understanding the design, installation, testing, and maintenance of earthing grids, engineers and technicians can ensure a safe and efficient electrical network.

If you have commercial electrical needs, contact Wilken for expert solutions tailored to your specific requirements. From earthing grid installation to comprehensive electrical services, Wilken provides reliable and safe solutions for your business.