Shield Wire Sag Calculator Inputs
Formula Used
Parabolic sag approximation: s = wL² / 8H, where s is sag, w is distributed load, L is span, and H is horizontal tension.
Ice load per meter: wice = Aice × ρ × g, where the annular ice area is based on wire diameter and radial ice thickness.
Wind load per meter: wwind = p × D, where p is wind pressure and D is the iced outside diameter.
Resultant load: wr = √(wvertical² + wwind²), combining vertical and horizontal distributed loads.
Thermal tension adjustment: ΔH = E × A × α × ΔT. The calculator uses this simplified elastic estimate to adjust the working horizontal tension.
Support tension: T = √(H² + (wL/2)²), giving the resultant end tension under the selected loading condition.
How to Use This Calculator
- Enter the actual span length and both support heights.
- Provide the shield wire geometry, area, and bare weight.
- Enter the initial horizontal tension and material properties.
- Add initial and final temperatures for thermal adjustment.
- Include wind pressure, ice thickness, and ice density for weather loading.
- Provide rated breaking strength and a safety factor for a design check.
- Press the calculate button to show sag, clearance, tension, and utilization above the form.
- Use the chart to compare thermal and loaded profiles, then export the result table as CSV or PDF.
Example Data Table
| Span (m) | Wire Weight (N/m) | Wind Pressure (N/m²) | Ice Thickness (mm) | Horizontal Tension (N) | Loaded Sag (m) |
|---|---|---|---|---|---|
| 180 | 7.20 | 350 | 0 | 15000 | 2.04 |
| 220 | 8.10 | 450 | 2 | 16500 | 3.34 |
| 280 | 8.90 | 500 | 3 | 18000 | 5.29 |
| 320 | 9.50 | 600 | 5 | 19500 | 7.58 |
| 380 | 10.30 | 650 | 6 | 21000 | 10.60 |
FAQs
1. What does this calculator estimate?
It estimates shield wire sag, support tension, weather loading, swing angle, and midspan clearance. It also compares the loaded tension against rated breaking strength using your chosen safety factor.
2. Which sag equation is used here?
The page uses a parabolic sag approximation. It is practical for many design checks and field reviews, especially when the sag-to-span ratio is modest and the span is treated as uniformly loaded.
3. Why include wind and ice?
Wind adds horizontal load, while ice increases vertical load and outside diameter. Together they raise the resultant loading, which can increase sag, change swing angle, and affect support tension significantly.
4. How is temperature handled?
The calculator applies a simplified elastic adjustment to horizontal tension using thermal expansion, material stiffness, area, and temperature change. Higher temperatures generally reduce tension and increase sag.
5. Is the clearance value the lowest conductor point?
The reported clearance is the loaded midspan clearance relative to the ground elevation reference you entered. Actual lowest clearance can shift on uneven terrain or under more detailed catenary analysis.
6. What is design status checking?
The status compares rated breaking strength against the loaded support tension multiplied by the safety factor. A pass means the entered strength meets or exceeds that simplified requirement.
7. Can I use this for final transmission line design?
It works well for preliminary studies, comparisons, and quick checks. Final design should still follow project criteria, code requirements, manufacturer data, and detailed sag-tension methods.
8. What units should I use?
Use meters, millimeters, newtons, square millimeters, kilograms per cubic meter, gigapascals, and degrees Celsius exactly as labeled. Keeping units consistent is essential for meaningful results.