Transmission Line Route Survey and Profile Design 

Designing a transmission line involves two critical steps at the initial stage:

1. Route Survey – identifying the most feasible and economical path for the transmission line.

2. Profile Design – creating the longitudinal profile (vertical alignment) of the selected route to assist in tower spotting and design.

Below is a detailed methodology for both:

1. Transmission Line Route Survey

Objective:

To determine the most optimal, technically feasible, economically viable, and environmentally acceptable route for the transmission line.

Methodology:

A. Pre-Survey Activities

1. Desktop Study:

   • Collect topo maps, satellite imagery, and GIS data.

   • Review terrain (plains, hills, rivers), land use (forests, agriculture, urban areas), and access roads.

   • Identify constraints: national parks, heritage zones, aviation paths, etc.

2. Regulatory Checks:

   • Review right-of-way (ROW) regulations.

   • Check permissible clearances from railways, roads, buildings, and rivers.

   • Study environmental and forest clearance requirements.

3. Initial Route Planning:

   • Identify 2–3 alternate alignments on maps or GIS tools.

   • Prefer straight and short routes minimizing angle points and crossings.

B. Field Survey

1. Reconnaissance Survey:

   • Verify alignment on the ground.

   • Note terrain conditions, obstacles, settlements, and access roads.

   • Modify alignment where necessary.

2. Detailed Route Survey:

   • Use GPS, Total Station, or Drone Survey methods.

   • Fix angle points and intermediate points at regular intervals (~300–400 m in plains; closer in hilly terrain).

   • Take levels at each point.

   • Record coordinates (latitude, longitude), elevation, and terrain features.

   • Identify river crossings, highway crossings, railway crossings, etc.

3. Soil Investigation (Preliminary):

   • Visual soil classification or shallow boreholes at key locations.

2. Profile Design of Transmission Line

Objective:

To create a longitudinal section along the finalized route to assist in tower spotting and structure design.

Methodology:

A. Data Collection:

• Use data from route survey: coordinates, elevation points.

• Employ surveying tools: Theodolite, Total Station, GPS, LiDAR, or Drone Survey.

B. Preparation of Longitudinal Profile:

1. Plot Chainage vs Elevation:

   • Plot ground profile (elevation) along the route at measured intervals.

   • Indicate angle points, terrain features, and crossing locations.

2. Superimpose Tower Positioning:

   • Decide tower spans based on terrain, conductor sag, and clearances.

   • Use tower spotting software or manual calculation.

   • Show tower type (suspension, tension, angle) and position.

3. Clearance and Sag Calculations:

   • Ensure minimum clearance from ground, roads, buildings, etc.

   • Check conductor sag and tension under various conditions (max temperature, wind load).

4. Drawing Preparation:

   • Generate profile drawing showing:

     • Terrain

     • Tower locations

     • Ground clearance

     • Span lengths

     • Obstructions

Tools and Technologies Used

ToolPurpose

GIS/Remote SensingRoute alignment & terrain mapping

GPSGround positioning and route tracking

Total StationAccurate elevation and distance measurement

Drone/LiDAR SurveyHigh-resolution terrain and profile data

AutoCAD/Civil 3DProfile drawing preparation

PLS-CADD / SAG10Tower spotting, sag-tension calculations

Best Practices

• Avoid forest land, if possible, to reduce environmental clearances.

• Avoid high-cost crossings like wide rivers or highways unless necessary.

• Coordinate with stakeholders early (utility companies, local authorities, etc.).

• Ensure all data is geo-referenced and well documented.