What are the steps to design an effective grounding system for a substation?

2 Soil resistivity

The second step is to measure the soil resistivity at different depths and locations around the substation site. Soil resistivity is a key factor that influences the resistance of the grounding system and the potential gradients on the surface. The soil resistivity can vary significantly depending on the soil type, moisture, temperature, and composition. Therefore, it is important to use accurate and reliable methods and equipment to obtain representative values. The soil resistivity data can be used to model the soil layers and select the appropriate grounding grid depth and spacing.

3 Grounding grid design

The third step is to design the grounding grid using software tools or analytical methods. The grounding grid is a network of buried conductors that interconnects the substation structures, equipment, and grounding rods. The grounding grid design should aim to minimize the grounding resistance, the touch and step voltages, and the potential rise of the substation during fault conditions. The grounding grid design should also comply with the relevant standards and codes, such as IEEE 80, IEC 60364, or NEC 250.

4 Grounding connections

The fourth step is to design the grounding connections between the grounding grid and the substation equipment, structures, and fences. The grounding connections should provide a low-impedance path for the fault currents and ensure the equipotential bonding of all metallic parts. The grounding connections should also be robust, durable, and corrosion-resistant. The type and size of the grounding connections depend on the current rating, fault duration, material, and installation method.

5 Grounding testing

The fifth step is to test the grounding system after installation to verify its performance and compliance with the design specifications and standards. The grounding testing should measure the grounding resistance, the soil resistivity, the touch and step voltages, and the continuity and integrity of the grounding connections. The grounding testing should also identify and correct any defects or deviations from the design. The grounding testing should be conducted by qualified personnel using calibrated instruments and following proper procedures.

6 Grounding maintenance

The sixth and final step is to maintain the grounding system throughout its service life to ensure its reliability and safety. The grounding maintenance should include regular inspections, measurements, cleaning, and repairs of the grounding system components. The grounding maintenance should also monitor and address any changes in the soil conditions, the substation configuration, or the fault current levels that may affect the grounding system performance. The grounding maintenance should be documented and recorded for future reference.