Calculator
Example Data Table
| Example | Span m | Weight N/m | Tension N | Wind N/m² | Ice mm | Temperature Change °C | Use Case |
|---|---|---|---|---|---|---|---|
| Level light span | 150 | 8 | 12000 | 0 | 0 | 20 | Basic classroom sag example |
| Wind loaded span | 250 | 12 | 18000 | 350 | 0 | 35 | Preliminary design check |
| Iced conductor | 300 | 14 | 22000 | 250 | 8 | 10 | Cold weather load review |
| Unequal supports | 220 | 10 | 16000 | 150 | 0 | 25 | Sloped terrain example |
Formula Used
Ice load: wi = π[(D/2 + t)² - (D/2)²] × ρ × g
Wind load: ww = p × (D + 2t)
Resultant load: W = √[(wc + wi)² + ww²]
Midspan sag: S = W × L² ÷ (8H)
Conductor profile: y(x) = left height + Δheight × x/L - W × x(L - x) ÷ (2H)
Thermal elongation: ΔLt = arc length × α × ΔT
Elastic elongation: ΔLe = arc length × H ÷ (E × A)
Final length: final length = sagged arc length + thermal elongation + elastic elongation
How To Use This Calculator
Enter the span length, conductor weight, and horizontal tension first. Add both support heights when the line is not level.
Enter diameter, wind pressure, ice thickness, and ice density when weather loading should be included. Use zero for wind or ice when they do not apply.
Enter the initial and final temperatures. Add the thermal expansion coefficient, modulus, and conductor area for elongation checks.
Press Calculate to show results below the header and above the form. Use the CSV or PDF buttons to export the same calculation.
Transmission Line Sag And Elongation Guide
Why Sag Matters
Overhead conductors do not stay straight between supports. They form a curve because weight acts downward. Wind and ice can add more load. Sag is the vertical drop between the support chord and the conductor. Too much sag can reduce ground clearance. Too little sag can raise tension and stress the conductor. Both conditions can create unsafe designs.
How The Calculator Helps
This calculator combines span length, conductor weight, wind pressure, ice loading, tension, support heights, temperature change, area, and modulus. It estimates resultant load first. Then it calculates midspan sag and the lowest point location. It also samples the conductor profile to find the minimum clearance above level ground. This makes the result useful for quick examples and early design checks.
Elongation In Practice
Conductors become longer when temperature rises. They also stretch under tension. Thermal elongation depends on the coefficient of expansion and the temperature difference. Elastic elongation depends on stress, modulus, and area. The final length is the sagged arc length plus both elongation values. This estimate helps explain why hot weather often increases sag.
Important Engineering Notes
The formulas use a parabolic sag model. This is common for moderate spans where sag is small compared with span length. Very long spans may need a catenary method. Real projects should also include code rules, vibration, creep, construction tolerances, emergency loading, and conductor manufacturer data. Always verify field decisions with a qualified engineer.
Example Workflow
Start with span and support attachment heights. Enter conductor unit weight and horizontal tension. Add diameter, wind pressure, and ice thickness when weather loading matters. Enter temperature data for elongation. Review sag, final length, clearance margin, and load components. Export the calculation when you need a record for review or comparison.
Best Use Cases
Use this tool for classroom examples, preliminary routing, maintenance discussions, and quick what if checks. It can compare several span choices before detailed design starts. Change one input at a time. Watch how sag, length, and clearance respond. That habit builds better judgment and reduces mistakes during planning. Keep records of assumptions. Small input changes can move results. Compare normal, cold, and hot cases carefully before selecting final stringing values.
FAQs
What is transmission line sag?
Sag is the vertical drop of a conductor below the straight chord between two supports. It happens because the conductor has weight and is held under tension.
What is conductor elongation?
Conductor elongation is the increase in conductor length. It can come from temperature rise, elastic stretch under tension, long term creep, or installation conditions.
Which sag model does this tool use?
This tool uses a parabolic sag model. It is suitable for many moderate span examples where sag is small compared with the span length.
Does wind increase sag?
Wind adds horizontal load. The calculator combines vertical and wind loads into a resultant load. That resultant load changes sag and conductor length estimates.
How does ice affect the result?
Ice adds weight around the conductor. More ice increases vertical load, sag, arc length, and clearance risk. Enter zero when ice is not present.
Why is tension important?
Higher horizontal tension reduces sag, but it increases conductor stress. Lower tension increases sag and may reduce ground clearance.
Can I use unequal support heights?
Yes. Enter different left and right support heights. The calculator estimates the line profile and finds the lowest clearance by sampling points across the span.
Is this enough for final design?
No. Use it for examples and preliminary checks. Final transmission designs should follow local codes, utility standards, field surveys, and qualified engineering review.