Key construction mistakes in high-voltage substations
Small deviations during substation construction can lead to major grounding, thermal, and mechanical problems that affect safety, reliability, and long-term performance.
Image for illustrative purposes
High-voltage substations, whether AIS or GIS installations operating up to 400 kV, are designed with strict engineering assumptions. Soil models, thermal limits, conductor behaviour, lightning protection angles, and the characteristics of CTs, VTs, and relays all form part of a precise design intended to keep operating conditions safe. In practice, however, construction activities on site often diverge from these requirements, and even small deviations can introduce serious risks.
Issues such as incorrect gravel thickness, misplaced grounding conductors, shield wires tensioned at the wrong temperature, or cable trays packed more tightly than expected may appear minor during construction. Yet in a high-energy environment, these deviations can lead to elevated step and touch voltages, overheating, mechanical overstress, lightning protection failures, CT saturation, and premature insulation problems.
These challenges appear across EPC projects worldwide and are particularly common in fast-track renewable connections, where tight schedules can compromise construction accuracy. The consequences affect not only safety and commissioning performance but also long-term reliability.
A key example is grounding design. The grounding study typically assumes specific gravel thickness, controlled resistivity, and accurate conductor spacing. In reality, gravel layers are often thinner than specified, compacted by machinery, or applied unevenly. Waterproofing layers under foundations, which behave as unintended insulators, further distort the grounding system by preventing concrete and rebar from bonding electrically with the soil. Enlarged mesh openings, rerouted conductors, and soil-improvement layers not included in the original soil model all contribute to unsafe voltage gradients and failed commissioning tests.
These problems demonstrate the importance of ensuring that construction practices follow engineering design from the first excavation to final energisation. In grounding, cable routing, sag and tension implementation, and CT/VT installation, accuracy is not optional, small deviations have significant operational impact.
Source: EEP
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