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The dielectric loss is also referred as Tan delta , Dissipation factor or Loss tangent.

When alternating current passes through the capacitor current leads the voltage by 900 when dielectric K is introduced between the capacitor the molecules of dielectric fail to align instantaneously with the alternating electric field. These molecules do not keep in phase with changing field. The angle of leading current is slightly reduced. New lead angle is Ø. Value 90-Ø is known as loss angle and is given by symbol δ . The power factor is defined as cos Ø and the dissipation factor as tan δ. For small values of d sin d (Power Factor) and tan d (dissipation factor) are almost equivalent. Also quoted in the literature is the loss factor which is numerically the product of dissipation factor and the dielectric constant.

Polar molecules exhibit high dielectric power losses at certain frequencies. The maximum power loss corresponds to the point of inflection in dielectric constant frequency curve. At low frequencies dipoles are able to keep in phase with changes in electric field and power losses are low. As frequency is increased the point is reached when dipole orientation cannot be completed in time available and the dipole becomes out of phase. This internal friction leads to generation of heat. Power factor and dissipation factor are measure of this energy absorbed by dielectric from the electric field per cycle.

When frequency is increased further there is no time for substantial dipole movement so power losses are reduced.

Dielectric Loss is strongly dependant on temperature.