EHV Transmission Line Survey – Flow Chart & Critical Observations

Basic Stages of an EHV Transmission Line Project

When a utility or power-transmission company sets out to build an Extra High Voltage (EHV) transmission line, the project must proceed through multiple well-defined stages. Each stage has its own inputs, deliverables, risks and decision-points. The key basic stages are:

1. Planning
   In this initial step the project scope, objectives, system requirement (voltage level, length, route region, end points) and broader constraints (e.g., environmental, regulatory, stakeholder) are laid out.
2. Feasibility Studies
   During this stage technical and cost feasibility are assessed: load flow, network integration, route estimates, basic cost-benefit, preliminary stakeholder identification, potential permit & land issues.
3. Study of Land Use, Topography, Subsurface Strata, and Major Crossings
   This is a vital investigative stage often overlooked. It involves detailed desktop studies and field reconnaissance to understand land-use patterns, terrain and topography, soil/subsurface strata conditions (which affect foundations), existing LT/HT/EHV line networks (which affect crossings and interference) and major obstacles such as rivers, highways, railways.
4. Investigation of Alternative Alignments with Cost Optimisation
   Having gathered detailed terrain / land/ network data, the team investigates multiple possible alignments, compares costs, minimises length and crossings, avoids difficult terrain/soil & makes sensible trade-offs.
5. Detailed Survey along the Selected Alignment
   Once a preferred alignment is chosen, a detailed survey is performed—setting out accurate survey control, tower locations, ground elevations, crossing details, etc.
6. Tower Optimisation using Specialised Software (e.g., PLS-CADD)
   Finally, with the survey data, detailed modelling is done using tools such as PLS‑CADD (Power Line Systems) to optimise tower type, spacing, conductor sag and clearance, foundation design and alignment adjustments.

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The Critical Stage That Is Often Ignored

Although stage 3—Study of Land Use, Topography, Subsurface Strata, and Major Crossings—is arguably the most crucial, in practice many projects skip it entirely. Instead, they jump straight to stage 5 (Detailed Survey), and this is a major root cause of alignment inefficiencies, cost overruns and technical problems.

Here is how things typically play out:

• A so-called “surveyor” gets deployed from day one. In many cases this person may know how to operate a total station or GPS, but lacks deeper transmission-line domain knowledge.
• The project team treats this activity as the “survey” and thinks the alignment decision is done once the field points are recorded.
• But if the surveyor has little understanding of tower types, base dimensions, existing line networks, crossings, sub-surface geotechnical conditions, then the recorded data is simply a set of points—not an alignment engineered for cost, reliability and constructability.
• The result? When the data is processed into PLS-CADD or similar software, you may discover difficult foundations, unexpected long spans, major crossings or costly right-of-way issues that could have been avoided if the early investigative stage had been done properly.

In short: the tool changes, but the substance remains unscientific. Using modern survey instruments or a fancy software-model does not magically fix the fact that the data fed in is weak or mis-aligned.

Many project heads exacerbate this by insisting survey teams be deployed immediately—without completing the crucial desktop work and walk-over reconnaissance (stages 3 & 4). In such cases the logical flow of project development is derailed, and the survey becomes the alignment decider—even though that’s not how it should work.

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Why Stage 3 and 4 Must Dominate Project Time

A disciplined and best-practice execution sequence would allocate approximately 90% of project time to the early stages (desktop studies, field reconnaissance, alignment alternatives) and only about 10% of time to the detailed survey and tower optimisation. Here’s why:

Why heavy investment in Stage 3 – Land Use/Topography/Subsurface/Networks

• Land-use patterns (e.g., agriculture, forest, urban, protected areas) determine right-of-way cost, permission hurdles and relocation burdens.
• Topography and terrain influence tower heights, span lengths, clearances and complexity.
• Subsurface strata (rock, soil, water tables) determine foundation type, cost and risk of settlement or difficult excavation.
• Existing LT/HT/EHV line networks create mandatory spacing and clearance constraints, and major crossing issues with highways/railways/bridges may have heavy permit burdens.
• Missing any of these means you may only discover a high-cost crossing or hard soils when you are already deep in survey and modelling.

Why Stage 4 – Investigation of Alternative Alignments – matters

• With the input from stage 3 you can generate multiple alignment options: long span but easy terrain, shorter route but difficult soils, avoid urban but longer cost route, etc.
• Cost-optimisation comes from exploring alternative alignments and selecting the best trade-off between length, terrain, construction cost, rights-of-way cost and lifespan cost.
• Without this work you are locked into the first straight-line survey alignment—a “least-resistant” choice, not the optimal one.

Survey and optimisation (Stages 5 & 6) are much more efficient once the groundwork is done

• Once the alignment is settled and the major constraints known, detailed survey is a focused engineering activity: setting towers, mapping detailed elevations, preparing inputs for optimisation software.
• The modelling step then uses robust data rather than weak “as-surveyed” points with hidden hassles.
• Tower optimisation is more accurate, cost-effective and constructable when based on well‐selected alignment.

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The Consequences of Skipping or Short-Changing Stage 3 & 4

When the early investigative steps are ignored or under-resourced, the project faces multiple risks:

• Major cost overruns due to expensive foundations, long spans, difficult crossings or extra right-of-way compensation.
• Delays from permit/relocation issues, land acquisition problems or unanticipated terrain difficulties.
• Poor alignment that may not optimise the network performance or may create operational issues (e.g., increased losses, difficult maintenance).
• Risk of failure or forced redesign later in the project when the “survey-driven” alignment proves sub-optimal.
• Pseudo claims of “modern survey” and “PLS-CADD modelling” may mask an underlying weak foundation in investigation.

In the end the transmission line may get built, but with poor optimisation, higher lifecycle cost, and reduced reliability. You might say the project “went ahead” but it did so without the discipline and rigor required for sustainable, cost-effective execution.

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Correct Approach – A Disciplined Flow for Transmission Line Projects

Let’s restate the correct approach for a high-voltage transmission-line project, emphasising the principle that investigation precedes survey:

1. Planning & Feasibility
   Define the voltage level, system connection, approximate route region, capacity, permissions, stakeholder map.
2. Comprehensive Desktop Studies & Field Reconnaissance (Stage 3)
   • Map land-use, vegetation, protected areas, urban/forest/agriculture.
   • Study topography, terrain gradient, slope stability, river/stream crossings.
   • Analyse subsurface strata via geological maps, soil bore logs, water-table info if available.
   • Survey existing LT/HT/EHV line networks and major infrastructure crossings (rail/road/bridge).
   • Use handheld GPS and walk-over reconnaissance to validate desk data.
3. Alternative Alignments & Cost Optimisation (Stage 4)
   • Develop multiple route options based on the investigative data.
   • Compare length, terrain difficulty, right-of-way cost, foundation cost, crossing complexity.
   • Select the most feasible and cost-effective alignment.
4. Detailed Survey Along Selected Alignment (Stage 5)
   • Deploy survey teams only after alignment is finalised.
   • Establish control points, measure ground elevations, record tower locations, map obstacles, mark rights-of-way.
5. Tower Optimisation & Modelling (Stage 6)
   • Feed the survey data into PLS-CADD or similar, optimise tower types, spans, clearances.
   • Confirm foundation types, design parameters, conductor sag, network performance.
6. Execution & Construction
   • With a well-engineered alignment and optimised towers in place, construction proceeds with fewer surprises, better cost control and fewer delays.

By following this structured approach, you ensure that each alignment point selected is itself an engineered decision—not just a point measured by a surveyor.

ALSO READ: Nuclear Soil Compaction Test for Transmission Tower Foundations According to SEC Standards

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Conclusion

An EHV transmission line is far more than “a line plotted on paper by a surveyor.” Every alignment point, every tower location, every span is a project component with financial, technical, and regulatory implications. If you ignore the early investigative and alignment stages, you risk cost inefficiency, delays, poor optimisations and long-term operational issues.

The toolset (like modern total stations, GPS and PLS-CADD) matters—but only after you have done your homework. The discipline lies in devoting approximately 90 % of project time to desktop studies, field reconnaissance, alternative alignment analysis—and only 10 % to survey and tower modelling. Any project head who insists on deploying survey crews without prior investigation is failing in leadership and jeopardising project efficiency.

In short: investigation before survey is the only way to ensure sustainable, cost-effective, technically sound EHV transmission line execution. Get the groundwork right, and the rest follows more smoothly. Get it wrong—and you will pay for it in cost, delay and reliability.