Leakage Currents
The leakage current is that current which is set up in a dielectric due to its electrical conductivity.
in solid dielectrics the following two types of currents are distinguished :
(i)Volume Leakage current (ii) Surface leakage current
volume leakage current passes through the bulk of the dielectric from one plate to another.
Surface leakage current passes over the surface of dielectric .
Dielectric losses
while calculating the dielectric losses, usually, only the volume leakage current is taken in to
consideration .but there is also loss of certain amount of power due to surface leakage current
but this power is primarily dissipated into heat the surrounding atmosphere and this loss does not
influence the heating of the dielectric in most of the cases.
Breakdown Voltage and Dielectric strength
If the voltage across the plates is increased slowly, a stage is reached at which dielectric breakdown
and short circuiting of the plates may be caused. The voltage at which this occurs is called Breakdown Voltage.
this is also called disruptive voltage.
the intensity of the electric field at which breakdown occurs is called dielectric or electric strength
it is expressed in kv/cm or kv/mm.
Effects of breakdown
the effects of breakdown can be summed up as follows:
1.Electrical effects
the insulating resistance of the material starts deteriorating as the voltage approaches the breakdown value.the current indicates a rise with the time even though the voltage keep unchanged.
When the voltage exceeds this value, the breakdown takes place followed by production of spark and puncturing of medium.
2.Mechanical effects
The breakdown is accompanied by the perforation of the insulation ,whose nature depends on the applied voltage and time of application .it is significantly pronounced in all insulting material
The leakage current is that current which is set up in a dielectric due to its electrical conductivity.
in solid dielectrics the following two types of currents are distinguished :
(i)Volume Leakage current (ii) Surface leakage current
volume leakage current passes through the bulk of the dielectric from one plate to another.
Surface leakage current passes over the surface of dielectric .
Dielectric losses
while calculating the dielectric losses, usually, only the volume leakage current is taken in to
consideration .but there is also loss of certain amount of power due to surface leakage current
but this power is primarily dissipated into heat the surrounding atmosphere and this loss does not
influence the heating of the dielectric in most of the cases.
Breakdown Voltage and Dielectric strength
If the voltage across the plates is increased slowly, a stage is reached at which dielectric breakdown
and short circuiting of the plates may be caused. The voltage at which this occurs is called Breakdown Voltage.
this is also called disruptive voltage.
the intensity of the electric field at which breakdown occurs is called dielectric or electric strength
Effects of breakdown
the effects of breakdown can be summed up as follows:
1.Electrical effects
the insulating resistance of the material starts deteriorating as the voltage approaches the breakdown value.the current indicates a rise with the time even though the voltage keep unchanged.
When the voltage exceeds this value, the breakdown takes place followed by production of spark and puncturing of medium.
2.Mechanical effects
The breakdown is accompanied by the perforation of the insulation ,whose nature depends on the applied voltage and time of application .it is significantly pronounced in all insulting material
0 comments: