Dielectric

In reality the dielectric is not an ideal insulator, i.e. a certain number of electrons penetrate it. Due to these processes and also to changing polarization in the material, part of the electric energy is lost as dissipated heat:

a)	Ohmic losses: there is a difference between insulation resistance = volume resistance Rv (current flow through the interior of the insulator) and surface resistance = the external resistance Rs (current flow over the surface of the insulator due to humidity or dirt). Together they make up the complete resistance



The ohmic losses are to be seen in the rise of the temperature of the insulator which is often quite considerable.

b)	Dielectric losses (dissipation) are the result of the changing polarization of the elementary particles of the dielectric caused by alternating fields. They are transformed into oscillations (like little compass needles) and thus produce frictional heat. So, here too, part of the electric energy is lost in heat.

The losses amount to:



tan is the dissipation factor, it is the measurement of dielectric losses and is dependent on frequency. .