Electrical Engineering ⇒ Topic : Different type of Dielectric materials
Dielectric materials are essentially insulating materials. However while the function of an insulating material is to obstruct the flow of current, the function of dielectric material is to store electrical energy.
In solid dielectrics the following two types of currents are distinguished :
(i) Volume leakage current (ii) Surface leakage current.
The dielectric power loss may be given by
P = 2ΠfCV2 tan 6 watts
where V = voltage (volts)
C = actual capacitance of the dielectric (farads)
tan δ = dielectric loss tangent.
The intensity Of the electric field at which breakdown occurs is called the 'dielectric or 'electiic strength'.
It is expressed in kV/cm or kV/mm.
Elevation of temperature invariably reduces the dielectric strength.
In solid dielectrics three types of breakdown are possible :
(i) Electro-thermal (ii) Electro-chemical (iii) Purely electrical.
The quantity of heat given off by the solid dielectric to the cooler surrounding medium is directly proportional to
(i) temperature difference (ii) thermal conductivity of dielectric (iii) co-efficient of heat transmission of the surface of the dielectric to t.he ambient medium.
'Flashover' is an insulation failure by discharge between the electrodes over the surface of an insulator.
When the dipoles are created the dielectrics is said to be polarised or in a state of polarisation. Polarisation is a vector quantity.
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