Corona Calculator: Critical Disruptive Voltage, Visual Voltage and Corona Loss (Peek's Law)
Find the voltage at which corona starts on a transmission line and how much power it wastes above that.
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How this calculator works
Enter the conductor radius, the spacing between the conductors (the GMD for three phases), the line voltage, the frequency, the air temperature and pressure, and the surface factors.
The calculator finds the air density factor and the critical disruptive voltage Vc, then the visual critical voltage at which the glow can be seen.
If the line voltage is above Vc it gives the corona loss in kW per km for each phase and the total for the three phases.
Formulas used
- \delta = \frac{p}{101.325}\frac{293}{273 + t}
- V_c = 21.1\,m_0\,\delta\,r\ln\frac{D}{r}
- P = \frac{241}{\delta}(f + 25)\sqrt{\frac{r}{D}}(V - V_c)^2\times10^{-5}
Worked example
With the default numbers in the calculator above:
- Air density factor: 0.98
- Critical disruptive voltage (corona starts), per phase rms: 117.88 kV per phase, which is 204.17 kV between lines
- Visual critical voltage (the glow can be seen), per phase rms: 130.06 kV per phase, 225.27 kV between lines
- Corona loss (Peek), per km per phase: 0.54 kW/km per phase, 1.63 kW/km for the three phases
Change the numbers in the calculator to see the full working, every step, for your own case.
Common questions
What is corona?
The breakdown of the air around a conductor when the electric field at its surface is high enough. It shows as a faint glow and a hiss, and it wastes power.
What decreases corona?
A larger conductor radius, bundled conductors, a larger spacing and smooth surfaces.
Why does weather matter?
Rain and fog lower the critical voltage by about 20 percent or more, so the loss in foul weather can be many times that in fair weather.
How accurate is Peek's formula?
It is an empirical formula, good for an order of magnitude. Line designers use more detailed methods for high-voltage lines.
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Got a question about this? Ask an engineering question and get a plain-language answer with references.
Further reading: Kothari and Nagrath, Modern Power System Analysis; Wadhwa, Electrical Power Systems (corona).
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