The Flashover Voltage Calculator helps engineers and electricians estimate the minimum voltage required to initiate a flashover across an insulating medium like air or solid materials. Flashover is a dangerous electrical discharge over the surface of insulation, and calculating this value is essential in high-voltage system design, equipment testing, and ensuring safety margins in power transmission. The calculator is especially useful in power plants, substations, high-voltage laboratories, and industrial installations where voltage control is critical to system reliability and personnel safety.
Formula of Flashover Voltage Calculator
Flashover Voltage (V) = E_critical × d × K
Where:
V = Flashover voltage in volts
E_critical = Breakdown electric field strength of the medium (V/m)
d = Distance between electrodes or across the insulating path (m)
K = Correction factor based on external factors such as humidity, atmospheric pressure, surface pollution or moisture, and electrode geometry or material properties
Standard Assumption:
In clean, dry air at room temperature and sea level:
E_critical (air) ≈ 3 × 10⁶ V/m
Thus, under standard conditions:
Flashover Voltage (V) = 3 × 10⁶ × d
For example, if the distance is 0.01 meters (10 mm):
V = 3,000,000 × 0.01 = 30,000 volts
In environments with pollution or moisture, a correction factor K is applied. A polluted or humid atmosphere may lower the breakdown strength, so K can range between 0.5 and 1.5 based on test data.
Common Flashover Voltages in Air (Standard Conditions)
| Distance (mm) | Distance (m) | Flashover Voltage (V) |
|---|---|---|
| 1 mm | 0.001 m | 3,000 V |
| 5 mm | 0.005 m | 15,000 V |
| 10 mm | 0.01 m | 30,000 V |
| 25 mm | 0.025 m | 75,000 V |
| 50 mm | 0.05 m | 150,000 V |
| 100 mm | 0.1 m | 300,000 V |
Note: These values assume dry air and no correction factor.
Example of Flashover Voltage Calculator
Let’s say you want to find the flashover voltage for a system with a 20 mm air gap under mildly humid conditions.
Given:
d = 0.02 meters
E_critical = 3 × 10⁶ V/m
K = 0.85 (based on test data for humid conditions)
Then:
V = 3,000,000 × 0.02 × 0.85
V = 51,000 volts
So, under these conditions, the flashover voltage is approximately 51 kV. To avoid flashover, voltage should be kept below this or insulation should be improved.
Most Common FAQs
A: Flashover voltage refers to the voltage at which current arcs across the surface of an insulator or air gap. Breakdown voltage usually refers to the voltage causing internal failure of the insulating material itself.
A: Yes. Higher humidity, pollution, and temperature can reduce the effective breakdown strength of air or insulating materials. Always apply an environmental correction factor (K).
A: Yes. Flashover can cause equipment failure, fires, and safety hazards. It should be prevented through proper insulation design and spacing using reliable calculations.