40054220 insulators

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NTRODUCTION

An insulator, also called a dielectric,

is a material that resists the flow of

electric current.

An insulating material has atoms withtightly bonded valence electrons.

Glass, plastic and rubberare excellent

insulators.

The term is also used more

specifically to refer to insulating

supports that attach electric power

transmission wires to utility poles or

pylons.
http://en.wikipedia.org/wiki/Dielectrichttp://en.wikipedia.org/wiki/Electric_currenthttp://en.wikipedia.org/wiki/Valence_electronhttp://en.wikipedia.org/wiki/Electric_power_transmissionhttp://en.wikipedia.org/wiki/Electric_power_transmissionhttp://en.wikipedia.org/wiki/Utility_polehttp://en.wikipedia.org/wiki/Electrical_pylonhttp://en.wikipedia.org/wiki/Electrical_pylonhttp://en.wikipedia.org/wiki/Utility_polehttp://en.wikipedia.org/wiki/Electric_power_transmissionhttp://en.wikipedia.org/wiki/Electric_power_transmissionhttp://en.wikipedia.org/wiki/Valence_electronhttp://en.wikipedia.org/wiki/Electric_currenthttp://en.wikipedia.org/wiki/Dielectric

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NTRODUCTION

Electric current flows from high voltage to

low voltage. The power line is high voltage.

The earth, or ground, is low voltage.

Anything in contact with the earth is also at

the same low voltage. That is why there areinsulators between the lines and the poles.

The higher voltage the lines, the bigger the

insulators.

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ISTORY OF INSULATORS

Insulators have been around longer than most people realize.

The first electrical systems to make use of insulators weretelegraphlines

The first rudimentary telegraph line was built between Paris andLille, France in 1793.

There were a number of early experimental lines in Europe andthe United States before Samuel F. B. Morse finally developed afully functional and commercial system using his particular code.

The first insulators were a beeswax soaked rag wrapped aroundthe wire.

Insulators have been around longer than most people realize.

The first electrical systems to make use of insulators were

telegraph lines

The first rudimentary telegraph line was built between Paris

and Lille, France in 1793.

There were a number of early experimental lines in Europe and

the United States before Samuel F. B. Morse finally developeda fully functional and commercial system using his particular

code.

The first insulators were a beeswax soaked rag wrapped

around the wire.
http://en.wikipedia.org/wiki/Telegraphhttp://en.wikipedia.org/wiki/Telegraphhttp://en.wikipedia.org/wiki/Telegraphhttp://en.wikipedia.org/wiki/Telegraphhttp://en.wikipedia.org/wiki/Telegraph

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ISTORY OF INSULATORS

In July 25,1865 that a carpenter,Louis A. Cauvet, invented thethreaded pinhole design we stillfind in insulators lying along oldrailroad tracks throughout thecountry.

It was a method for threadingthe inside pinhole of theinsulator, which then could bescrewed down on a threadedwood or metal pin as shown inthe figure.

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EQUIREMENTS

Mechanically strong.

High dielectricstrength.

Provide high insulationresistance to leakage current.

Free from internalimpurities.Should not b porous.

High range ofPuncturestrength to flash overvoltage.

Not affected by the change oftemperature

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EQUIREMENTS

Resistivity is a measure of how much current will be

drained away from the conductor through the bulk or

along the surface of the dielectric. An insulator with

resistivity equal to or greater than 10^13 ohm-cm maybe considered good.

For high-voltage (on the order of kilovolts) applications,

dielectric strength is the most important single propertyof the insulation.

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YPES OF INSULATORS

Based on material

1.Porcelain

2.Glass

3.EPDM Rubber

4.PVC

Based on use (location)1.Pin insulator

2.Disc insulator(Suspension-Strain)

3.Post insulator

4.long rod insulator

5.Shackle insulator

6.Guy insulator

Based on Voltage

1.L.T (Low Tension)

2.11kv

3.33kv

4.132kv

5.220kv

6.400kv or above

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YPES OF INSULATORS

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IGH VOLTAGE INSULATORS

High voltage insulators, as thename suggests, are used toelectrically insulate pylons from

live electrical cables.

H.V. line insulators may consistof a string of insulatorunits,depending on insulator

type and application.

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Different types of line insulatorsare used, in H.V. lines dependingon voltage and mechanical strain(tension) requirements. The

more widely used types are asfollows.

1)Disc type: where insulationdiscs (also called insulation

units) are strung togetherdepending on the insulation leveldesired.
http://www.adaptaust.com.au/Porcelain_Insulators.htmhttp://www.adaptaust.com.au/Porcelain_Insulators.htm

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Each disc is typicallyrated at 10-12kV, with acapacitance of30-40pF.

Discs are strung togethervia their caps andpins. Lockingmechanisms may be ball-socket or clevis-tongue

type. The cap isinsulated form the pin viathe porcelain (or glass)disc.

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2)Longrod type. These may also bestrung together for higher insulationand may have similar ball-socketand clevis-tongue lockingmechanisms.

Theirlonger length makes themapplicable forphase-to-phaseinsulation to reduce line gallopingduring strong winds.

Both disc and longrod-typeinsulators are commonly used insuspension or strain (tension)insulator applications.
http://www.adaptaust.com.au/Porcelain_Insulators.htmhttp://www.adaptaust.com.au/Porcelain_Insulators.htm

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3)Pin type. Pin types are screwedonto a bolt shank secured on thecross-arm of the transmission poleor pylon. The pin type does nottake main transmission line strain

(tension) , and functions as ajumper line insulator.

4)Shackle type insulators . Theseare mostly applied to support linestrain (tension), such as at changesof transmission line direction .

5)Post type. These may havethicker insulation and more discsthan pin types and can be mountedvia clamp or pinmethod. These areonly be applied in 11kv & 33kv .
http://www.adaptaust.com.au/Porcelain_Insulators.htmhttp://www.utilex.com/lowtension.htmhttp://www.adaptaust.com.au/Porcelain_Insulators.htmhttp://www.adaptaust.com.au/Porcelain_Insulators.htmhttp://www.utilex.com/lowtension.htmhttp://www.adaptaust.com.au/Porcelain_Insulators.htm

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6)Hewlett type. A variation of the disctype, but can take more mechanicalstrain due to internally insulated steelbolt interlocks holding discs togetherinstead of cement. On the other hand,

the Hewlett type has higher internalelectricalstress due to its internalsteel bolts.

7)Pot type[13], which are usually pinmounted and often used with

telephone lines.
http://www.r-infinity.com/Hewlett/index.htmhttp://www.r-infinity.com/Hewlett/Page2.htmhttp://www.r-infinity.com/Hewlett/Page2.htmhttp://teleramics.com/inuse/inuse2003.htmlhttp://knol.google.com/k/adam-junid/overhead-line-insulators/22z3waum2dn6b/2http://knol.google.com/k/adam-junid/overhead-line-insulators/22z3waum2dn6b/2http://teleramics.com/inuse/inuse2003.htmlhttp://www.r-infinity.com/Hewlett/Page2.htmhttp://www.r-infinity.com/Hewlett/Page2.htmhttp://www.r-infinity.com/Hewlett/index.htm

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ERMINOLOGY

When applying insulators it is necessary to desctribe the insulator dimensionusing the following terms:

CREEPAGE DISTANCE : The shortest distance between the metalware atthe 2 ends of the insulator excluding the intermediate metal fittings.

SPECIFIC CREEPAGE DISTANCE : It is the ratio of the creepage distance inmm to the line-to-line rms voltage of the 3-phase system in kv.

CONNECTING LENGTH : It is the axial length of the insulators between thetwo terminals.

ARCING DISTANCE : The distance between the metalware,measured as thelength of a tightly pulled piece of string.

INTERSHED SPACING : Distance between corresponding points on adjacentsheds.

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ESIGN

Design and manufacturing care is taken tohave both electrical insulation andmechanical strength .

1) Dimensions such as shed and

creepage distances may be adjusted forservice in high pollution environments(with or without rainwashing), areas ofairborne sea salts, icing and bird riskareas. Extra creepage distances are usedto avoid inadvertent flashover in suchhighlyionised atmospheres or areas withlarge bird sizes (e.g. Sudan, North

America).

2) Insulation materials may only be drilledor cored parallel sided, and may only behot-punched at forging temperatures.
http://localhost/var/www/apps/conversion/tmp/scratch_10/insulators/Overhead%20Line%20Insulators%20-%20a%20knol%20by%20Adam%20Junid_files/fig11-bird-protection-hillforce-airbase.jpg

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ESIGN

3) Dirt, pollution, salt, and particularly water on the surface of ahigh voltage insulator can create a conductive path across it,causing leakage currents and flashovers.

Hence these are shaped to maximise the length of the leakagepath along the surface from one end to the other, called thecreepage length, to minimize these leakage currents.

Minimum creepage distances are 20-25 mm/kV, but must be

increased in high pollution or airborne sea-salt areas.

4) Also to identify the fault in its top and the flow of rain watereasily insulators are generally made brown.

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OMPANIES

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ONCLUSION

During the earlier part of this century

ceramics,glass & porecelain have been establised

as reliable materials for high voltage insulation.

Over the past few decades,new technologies

involving polymeric materials have increasingly

been used for transmission & distribution

systems.These insulators have many advantagesover other materials.

40054220 insulators

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