BREAKDOWN IN SOLID INSULATING MATERIALS

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.

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.

Types of Solid Insulator

Paper Porcelain Ceramic

Rubber PVC Mica Wood

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

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.

Tracking

Tracking is the formation of the

permanent conducting path across

a surface of the insulation.

Only organic material.

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.

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.

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.

This compression decreases the dielectric

thickness thus increasing the effective stress

Pc =1/2 €0 €r V2 /d2