presentation on breakdown in solid insulator
TRANSCRIPT
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BREAKDOWN IN SOLID INSULATING MATERIALS
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The Power Group08EL-02 M. Tariq Mustafa
08EL-47 Muhammad Younis
08EL-49 M. Imran Ali
08EL-50 Umer Hafeez
08EL-51 Mujahid Hussain
08EL-59 Mudassar Nazeer
08EL-60 Shafqat Hussain Sabaaq
University College of Engineering & Technology,
The Islamia University of Bahawalpur, Pakistan.
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BREAKDOWN OF THE INSULATING MATERIAL
It is a state in which a dielectric material loose its insulating properties and provides a conducting path for the current to flow through it.
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Types of Solid Insulator
Paper Porcelain Ceramic
Rubber PVC Mica Wood
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Surface flashover is a breakdown of the medium in which the solid is
immersed.
The role of the solid insulating material is only to distort the field so that
the electric strength of the gas is exceeded.
The three essential components of the surface flashover phenomenon
◦ Presence of the conducting film across the surface of the insulation
◦ Leakage current through the conducting film
◦ Degradation of the insulation.
3.Surface breakdown
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Conducting film is usually moisture from the
atmosphere due to contamination
Moisture is not only a conducting path, it can also
arise from metal dust due to wear and tear of
moving parts.
For discharge to occur, there must be a voltage at
least equal to the Paschen Min. for the particular
state of the gas.
e.g.Paschen min. in air at N.T.P it is 380V, whereas
tracking can occur at well below 100V.
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Tracking
Tracking is the formation of the
permanent conducting path across
a surface of the insulation.
Only organic material.
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Erosion
In a surface discharge, if the products of
decomposition are volatile and there is no
residual conducting carbon on the surface, the
process is simply one of pitting, results erosion.
Occurs in organic materials.
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It is preferable to use materials with erosion
properties rather than tracking properties
As tracking makes insulation immediately
completely ineffective,
Whereas
Erosion only weakens the material but allows
operation until replacement can be made later.
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Electro-Mechanical BreakdownWhen an electric field is applied to a dielectric
between 2 electrodes, a mechanical force will be
exerted on the dielectric due to the force of
attraction between the surface charges.
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This compression decreases the dielectric
thickness thus increasing the effective stress
Pc =1/2 €0 €r V2 /d2