40054220 Insulators
Transcript of 40054220 Insulators
-
7/29/2019 40054220 Insulators
1/20
-
7/29/2019 40054220 Insulators
2/20
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 -
7/29/2019 40054220 Insulators
3/20
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.
-
7/29/2019 40054220 Insulators
4/20
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 -
7/29/2019 40054220 Insulators
5/20
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.
-
7/29/2019 40054220 Insulators
6/20
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
-
7/29/2019 40054220 Insulators
7/20
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.
-
7/29/2019 40054220 Insulators
8/20
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
-
7/29/2019 40054220 Insulators
9/20
YPES OF INSULATORS
-
7/29/2019 40054220 Insulators
10/20
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.
-
7/29/2019 40054220 Insulators
11/20
IGH VOLTAGE INSULATORS
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 -
7/29/2019 40054220 Insulators
12/20
IGH VOLTAGE INSULATORS
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.
-
7/29/2019 40054220 Insulators
13/20
IGH VOLTAGE INSULATORS
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 -
7/29/2019 40054220 Insulators
14/20
IGH VOLTAGE INSULATORS
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 -
7/29/2019 40054220 Insulators
15/20
IGH VOLTAGE INSULATORS
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 -
7/29/2019 40054220 Insulators
16/20
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.
-
7/29/2019 40054220 Insulators
17/20
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 -
7/29/2019 40054220 Insulators
18/20
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.
-
7/29/2019 40054220 Insulators
19/20
OMPANIES
-
7/29/2019 40054220 Insulators
20/20
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.