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Properties And Behavior Of

Composite & SolidInsulating Materials

By

Sachin Bhandari (EE03-64)

Tanmay Adke (EE03-67)

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Classifications Of Insulators

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Classes of Insulation

Following are the different classes ofinsulation

Y class (up to 90o C)

A class(up to 105o

C) E class (up to 120o C)

B class (up to 130o C)

F class (up to 155o

C) H class (up to 180o C)

C class (above 180o C)

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Solid Insulators

Following are the solid insulators

Glass Insulator Egg shapedstrain insulators

Ceramic

insulator

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Composite Insulators

Two commonly used elastomericmaterials are silicon rubber & EDPM(Ethylene propylene diene monomer)rubber

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A continuous strand of glass fiber is wetted in a controlled manner

in a liquid resin bath, and then wound between and aroundbushings.

The shield layer and weather sheds, both made of a polymer are

then injection molded over the body.

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Characteristics of Insulating Materials

Good insulating materials shall have thefollowing characteristics Good mechanical strength. Good heat conductivity.

Non-hygroscopic Must have the ability to withstand theallowable temperature without any changein the physical and chemical properties.

Composite insulators are less costly, lighterin weight, and have excellent hydrophobiccapability.

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Behavior of solid insulating materials

The highest breakdown strengthobtained under carefully controlledconditions is known as the "intrinsic

strength" of the dielectric.

Dielectrics usually fail at stresses

well below the intrinsic strength dueusually to one of the following

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Causes

electro-mechanical breakdown

breakdown due to internal

discharges surface breakdown (tracking and

erosion)

thermal breakdown electro-chemical breakdown

chemical deterioration

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Behaviour Of Different Insulating Materials

Fig. The switching impulse voltage is generated with a marxgenerator.

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Electro-mechanical breakdown

When an electric field is applied to adielectric between two electrodes, amechanical force will be exerted on thedielectric due to the force of attraction

between the surface charges. Thiscompression decreases the dielectricthickness thus increasing the effectivestress.

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Breakdown due to internal discharges

the electric field strength in the voids is

higher than that across the dielectric. Thuseven under normal working voltages, thefield in the voids may exceed theirbreakdown value and breakdown may

occur.

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Applications:

In over head Transmission lines Power Transformers

Rotating Machines

Circuit Breakers Cables

Power Capacitors

Electronic Equipments