Clearance calculations (based on Back Flash Over)
This tool lets you calculate the risk of an external flashover as a result of a back flash over caused by a lightning strike to a transmission line. This follows the statistical method as described in paper 10288, that was written for the Cigre Paris 2026 sessions and can be downloaded here for Cigre members (B2 package Cigre 2026).
External clearance - backflashover assessment
1. Conductor geometry
Import conductor geometry and all input values from a JSON configuration file.
Export conductor geometry and all input values to a reusable JSON configuration file.
| Type | D (cm) |
# | Spacing (cm) |
X (m) |
H (m) |
Req (m) |
|---|
2. Inputs
3. External clearance sweep
Example: 0.6, 0.8, 1.0, 1.2, 1.4, 1.6. These are absolute external clearance values in meters.
4. Results
Trendline analysis
Trendline formula: -
| External clearance (m) | Internal clearance (m) | Internal Ic (kA) | Closest external Ic (kA) | Rff total without protection |
MTBF without protection |
Rff total with protection |
MTBF with protection |
|---|
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This tool was developed for educational purpose.