Current version: v0.11.0-beta · Changelog · Live app
A browser-based tool for calculating overhead conductor tension from field sag measurements. Built to solve the practical difficulty of quickly verifying conductor tension in transmission lines using simple field instruments — primarily in mountainous and difficult terrain where traditional sag-tension charts are hard to apply.
Given a few field measurements (tower hook elevations and a single conductor sighting), TL-SAG computes:
- Horizontal Tension (T) in the conductor
- Equivalent mid-span sag for a level span
- Safety factor against Ultimate Tensile Strength (UTS)
- Compliance verdict per IS 398 / utility everyday tension guidelines
All computation runs entirely client-side in the browser — no server, no installation, no data leaves your device.
Shoot Z-elevations at Tower A hook, Tower B hook, and a conductor point using a Total Station or theodolite. The tool solves for tension using the parabolic sag equation:
T = (w × xp × (L − xp)) / (2 × D)
For mountainous terrain where you cannot position directly below the line — measure slant distances and angles from an off-axis viewpoint. The tool projects 3D rangefinder readings into the span plane to extract L, h, xp, and D.
Upload a photo of the span (shot as perpendicular to the span as possible). Mark the two tower hooks, then trace 10–20 points along the conductor — the tool least-squares fits a catenary y = y0 + C·(cosh((x−x0)/C) − 1) through the trace and extracts the catenary constant C = T/w, giving horizontal tension directly from the curve shape, plus max/mid-span sag and an RMS fit-quality score. A quick 3-point mode (hooks + lowest point) is also available.
Workspace features: scroll/pinch zoom, pan, magnifier loupe during point placement, drag-to-adjust any point, undo, and optional camera-roll correction by marking a plumb-vertical reference (e.g. tower body edge).
Image calibration methods:
- Perspective 4-Point (recommended) — mark both hooks and both tower bases; with the span length and tower structural heights, a planar homography rectifies the photo into true metres in the span plane. Handles oblique shots (span receding into a valley) and camera roll exactly.
- Chord calibration (square-on photos; known span L and height difference h)
- Tower height calibration (square-on photos; known tower height from drawings)
Calculate horizontal span L and height difference h from GPS hook elevations + slant distance, or from slant distance + angle of inclination.
Time a mechanical wave pulse reflected along the conductor to estimate sag from wave velocity.
- Catenary SVG visualizer that updates with your inputs
- Sag vs. Tension safety curve with UTS threshold bands
- Statistical sensitivity analysis with RSS error propagation
- Print-ready engineering report — annotated span photograph, span geometry sketch, results & calculation log
- Project-first workflow — work starts by creating/resuming a named project; everything auto-saves to the browser on this device
- Project save/load via local JSON export/import (backup & sharing between devices)
- Dedicated results page for analysis review
- Interactive sandbox visualizer (explanations.html) with sliders for each method
Open index.html in any modern browser. No build step required.
Open the live app once, then:
- iPhone (Safari): Share → Add to Home Screen → the app launches full-screen and works offline.
- Android (Chrome): ⋮ menu → Add to Home screen (or the install prompt).
On the phone, the photo workspace uses touch-native gestures: one finger pans, pinch zooms, and the ＋ Place button drops points exactly at the centre crosshair. Tip: on iPhone, Export projects you care about — iOS may clear browser storage after weeks of disuse.
To deploy as a static site (e.g. GitHub Pages), simply serve the repository root — all files are plain HTML/CSS/JS.
| File | Purpose |
|---|---|
index.html |
Main calculator application |
engine.js |
Pure calculation engine (no DOM) — sag/tension formulas, catenary least-squares fitter, error propagation. Unit-tested; reusable by the future mobile app |
app.js |
UI controller, visualizer logic, export/import |
phototracker.js |
Interactive photo canvas: zoom/pan/loupe, catenary tracing, roll correction |
style.css |
Application styling and layout |
explanations.html |
Interactive sandbox visualizer with physics explanations |
results.html |
Dedicated results analysis page |
tests/engine.test.js |
Engine unit tests — run node tests/engine.test.js, or open tests/index.html in a browser |
This project is released under the MIT License.
Initiated to solve practical field difficulties of quickly calculating conductor tension in transmission lines using simple tools available — primarily for mountainous areas of Himachal Pradesh, India.
Contributors: Keshav Attri, Parikshit Pal, Sanjay Negi — Power Transmission Engineers, Himachal Pradesh.
Conforms to IS 398 & Indian Standard Electricity Utility Guidelines