LOW DIELECTRIC LOSS (TAN DELTA)
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
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
Dielectric Loss is strongly dependant on temperature.