Measurement of Dielectric Constant and Loss Factor
Introduction to Dielectric Loss
- Dielectric constant is also called relative permittivity of the insulating material.
- Many of the insulating materials have dielectric constant more than unity.
- These materials show dielectric loss when subjected to AC voltages.
- Dielectric constant as well as dielectric loss depends on
- magnitude of voltage stress
- frequency of the applied voltage.
- Dielectric is generally used in ‘capacitors’ or cables. Variation of dielectric constant dielectric low with frequency is very important in such equipments.
- Generally variation of these two quantities w.r.t. frequency is combined together to be known as complex quantity or complex permittivity.
- The value of this is to be determined at different values of frequencies. In the ideal case current IC leads the voltage VC by exactly 90°.
- But in the actual case (capacitance with lossy dielectric) the angle of lead falls by some angle δ.
- This angle θ is called as loss angle. The current leads the voltage by less than 90° i.e.
- θ = (90-δ)o
- This relation is shown in below figures. =
- Loss Component IR = Voltage / Resistance of dielectric = V / R
