GITAM, Department of Engineering Physics
Dielectric Losses
DIELECTRIC LOSSES result from the heating effect on the dielectric material
between the conductors. Power from the
source is used in heating the dielectric. The heat produced is dissipated into
the surrounding medium. When there is no potential
difference between two conductors, the atoms in the
dielectric material between them are normal and the
orbits of the electrons are circular. When there is a
potential difference between two conductors, the
orbits of the electrons change. The excessive negative
charge on one conductor repels electrons on the
dielectric toward the positive conductor and thus distorts
the orbits of the electrons. A change in the path of
electrons requires more energy, introducing a power
loss. The
atomic structure of rubber is more difficult to distort than the structure of
some other dielectric materials. The
atoms of materials, such as polyethylene, distort easily. Therefore,
polyethylene is often used as a
dielectric because less power is consumed when its electron orbits are
distorted.
The dielectric loss
factor is defined as the tangent of the loss angle, tan
d , i.e. the ratio of the
imaginary part e"
to the real part e'
of the permittivity. In a parallel equivalent circuit of the ceramic
element, the loss factor represents the ratio of conductance Gp
to susceptance B.
tan d is also
the ratio of resistance Rs to reactance X of a
series equivalent circuit. The loss factor can be measured directly using
a capacitance bridge.
