Calculate dielectric strength from breakdown voltage and thickness, or estimate breakdown voltage or insulation thickness using air, SF6 or your own value.

Illustrative derating
Blank = 1 (no derating).

Related Calculators

Dielectric Strength Formula

The following formula is used to calculate the dielectric strength of a material.

DS = BV / T

Variables:

  • DS is the dielectric strength (kV/mm)
  • BV is the breakdown voltage (kV)
  • T is the material thickness (mm)

To calculate measured dielectric strength, divide the breakdown voltage by specimen thickness. The ideal reverse model uses BV = DS × T. Modeled thickness = operating voltage × chosen margin factor ÷ DS; derated voltage = BV ÷ chosen factor. Blank factor means 1 (no derating). Strength generally varies with thickness, so these relationships do not replace material-specific testing or qualified insulation design.

What is Dielectric Strength?

Dielectric strength is a measure of the electrical strength of a material as an insulator. It is the breakdown voltage divided by specimen thickness under specified test conditions. Values depend on specimen thickness, electrodes, temperature, humidity, frequency and test method; they are not universal safe working-field limits. Dielectric strength is typically expressed in kilovolts per millimeter (kV/mm). It is an important property for materials used in electrical insulation, as it indicates how much electric stress the material can endure before it fails.

How to Calculate Dielectric Strength?

The following steps outline how to calculate the Dielectric Strength.

  1. First, determine the breakdown voltage (BV) in kilovolts (kV).
  2. Next, determine the material thickness (T) in millimeters (mm).
  3. Use the formula from above = DS = BV / T.
  4. Finally, calculate the Dielectric Strength (DS) in kV/mm.
  5. After inserting the variables 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.

Breakdown Voltage (BV) = 30 kV

Material Thickness (T) = 2 mm. Therefore DS = 30/2 = 15 kV/mm under those test conditions.