# Dielectric Strength Definition

The dielectric strength is a property of a material which enables it to withstand electric stress without damage. It is usually expressed in terms of minimum electric stress (potential difference per unit distance) that will cause breakdown of dielectric under certain conditions of service. The dielectric strength of an insulator or dielectric material is given by the maximum potential difference which a unit thickness of the material can withstand without breaking down. It is usually expressed in kV/mm. For example, when we say that the dielectric strength of mica is 60 kV/mm, then it means that the maximum potential difference which one mm thickness of mica can withstand across it without breaking down is 60 kV or 60000 volts. If the potential difference exceeds this value, then mica insulation breaks down allowing a large current to pass through it.## Dielectric Constant

## Dielectric Constant Definition

**Dielectric constant is the ratio of the capacitance of a capacitor having a certain dielectric to the capacitance of the same capacitor with vacuum (or air) as the medium.**

- Let there be a parallel plate capacitor of capacitance C, which has no dielectric material.
- and when we place a dielectric material between its plates, its capacitance becomes C’.
- then, the dielectric constant of the dielectric material will be C’/C.

**The importance of dielectric constant lies in the fact that when an alternating voltage is applied to such a composite insulation, the voltage distribution across the insulation is found in inverse proportion to the dielectric constants of the materials involved.**For example, suppose there is an equal thickness of oil of dielectric constant 3 and paper of dielectric constant 4 in series. When a voltage is applied across it, 57% of voltage act across the oil and 43% across the paper. Therefore, while designing a composite insulation care must be taken that the composite insulating materials have an appropriate dielectric constant in order that dangerously high voltage does not appear across any one of them.

## Dielectric Loss

^{o}exactly and there will be no consumption of power. Only vacuum and purified gases approach this perfection.

## Dielectric Loss Definition

In most insulating materials that is not the case. There is a definite amount of dissipation of energy when an insulator is subjected to AC voltage. This dissipated energy is known as the dielectric loss.^{o}. The phase angle is always less than 90

^{o}. The complementary angle δ = 90 – θ is known as

**dielectric loss angle**. For an insulator having a capacitance

**C**and having a voltage

**V**applied to it at a frequency

**f**Hz, the

**dielectric power loss**can be calculated as:

**P = V**From the above equation, it is clear that power loss is dependent on tan δ so long as other factors are constant. Tan δ is known as power factor of the insulator. Thanks for reading about “dielectric strength definition, dielectric constant definition and dielectric loss definition”.

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