Enter the breakdown voltage, spark gap distance, pressure, and gas temperature into the calculator to estimate the missing variable.

High Voltage Spark Gap Calculator

Enter any 3 values to estimate the missing one (dry air, near-uniform field approximation).

Related Calculators

High Voltage Spark Gap Formula

The following approximation is used to estimate the breakdown voltage of a spark gap in dry air. Real gas breakdown follows Paschen’s law (and depends on gas type, electrode geometry, and the product of pressure and distance), so results from this simple model should be treated as a rough estimate.

V \approx E_0\,d\,\frac{P}{P_0}\,\frac{T_0}{T}

Variables:

  • V is the breakdown voltage in volts (V)
  • d is the spark gap distance (gap length) in meters (m)
  • P is the absolute gas pressure in pascals (Pa), and P0 = 101,325 Pa (1 atm)
  • T is the absolute gas temperature in kelvin (K), and T0 = 293.15 K (20 Â°C)

To estimate the breakdown voltage, multiply the gap distance by the approximate breakdown field strength of air at reference conditions (E0 ≈ 3×106 V/m, which is about 3 kV/mm or 30 kV/cm) and then scale by the relative air-density factor (P/P0)(T0/T).

What is a High Voltage Spark Gap?

A high voltage spark gap is a device used to create a controlled electrical discharge between two electrodes separated by a gap. The gap can be adjusted to control the voltage at which the spark occurs. Spark gaps are commonly used in high voltage applications such as lightning arresters, radio transmitters, and high voltage testing equipment. They work by ionizing the air or gas in the gap, allowing current to flow and creating a spark. The breakdown voltage depends on the gas (and humidity), electrode shape/spacing, and the gas density (which is affected by pressure and temperature).

How to Calculate High Voltage Spark Gap?

The following steps outline how to estimate the breakdown voltage of a High Voltage Spark Gap using the approximation above.

  1. First, determine the spark gap distance (d).
  2. Next, determine the pressure (P).
  3. Next, determine the gas temperature (T).
  4. Finally, estimate the breakdown voltage using the formula V ≈ E0d(P/P0)(T0/T).
  5. After inserting the values and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge. Using E0 ≈ 30 kV/cm at 1 atm and 20 Â°C, the estimated breakdown voltage for this example is about 45 kV.

Spark gap distance (d) = 1.5 cm

Pressure (P) = 1 atm

Gas temperature (T) = 20 Â°C