Ehv Ac Intro

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 EHV AC  CHAPTER I. INTRODUCTION High voltage is used in electric power distribution,in cathode ray tubes,to generate x-rays and particle beams and high power vacuum tubes and other scientific and industrial applications.Many Industrialcentered countries of the world thrive for a vast amount of energy in which electrical energy forms a major portion.There are se ve ral ty pe s of ener gy su ch as na tu ra l ga s for domest ic an d in du st ri al cons umpt io n, wh ic h form a co ns ider ab le proport io n of th e tota l energy consumption. Thus,we can say that theelectrical energy is not the only form in which energy is consumed but it is also an important part nevertheless.Today the world is on the verge of consuming the major portion of its natural resources in a very short spam of time and is already looing for alternative sources of energy excluding hydro and thermal to cater for the rapid rate of consumption which is outpacing the discovery of new resources.This will however does not slow down with respect to time and therefore there exists a need to reduce the rate at which energy consumption is increasing.Therefore,a tremendous need for energy is very urgent in many developing countries and their relation to other countries are sometimes based on the energy re!uirements."sually the Hydroelectric and coal or oil-fired stations are located very far from the load centres for various reasons which re!uires the transmission of the generated electric power over very long distances.This led to the re!uirement of very high voltages for transmission.  #xtra High $oltage %#H$& '.(. transmission may be considered to come when the first )*+++ $ line was put into service in weden. 'fter then,all the industriali/edcount ries all over the world have adopted the higher voltage levels. 0a te r it was ob served that the impact of such hi gh vo ltage levels on the environment needed careful attention because the use of high surface voltage gradients on conductors led to the interference problems from powerfre!uency to T$ fre !ue ncies. Thus cor ona effects,elec trosta tic fields in the line vic ini ty , losses,audible noise, carrier interference and radio interference became recogni/ed as steadystate problems which governs the line conductor design, line height, and  phase-spacing used to e ep the interfering fields wi thin prescribed limits."se o f synchronous condensers due to high line charging currents at load end only became impractical to control voltages at the sending-end and receiving-end  buses."se of hunt compensating reactors for voltage control at no load and switched capacitors at load conditions became necessary. . 'll these are still 1

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  EHV AC

  CHAPTER I. INTRODUCTION

High voltage is used in electric power distribution,in cathode ray tubes,to generate

x-rays and particle beams and high power vacuum tubes and other scientific and

industrial applications.Many Industrialcentered countries of the world thrive for a

vast amount of energy in which electrical energy forms a major portion.There are

several types of energy such as natural gas for domestic and industrial

consumption, which form a considerable proportion of the total energy

consumption. Thus,we can say that theelectrical energy is not the only form in

which energy is consumed but it is also an important part nevertheless.Today the

world is on the verge of consuming the major portion of its natural resources

in a very short spam of time and is already looing for alternative sources of 

energy excluding hydro and thermal to cater for the rapid rate of consumptionwhich is outpacing the discovery of new resources.This will however does not

slow down with respect to time and therefore there exists a need to reduce the rate

at which energy consumption is increasing.Therefore,a tremendous need for energy

is very urgent in many developing countries and their relation to other countries are

sometimes based on the energy re!uirements."sually the Hydroelectric and coal or 

oil-fired stations are located very far from the load centres for various reasons

which re!uires the transmission of the generated electric power over very long

distances.This led to the re!uirement of very high voltages for transmission.

 #xtra High $oltage %#H$& '.(. transmission may be considered to come when

the first )*+++ $ line was put into service in weden. 'fter then,all the

industriali/edcountries all over the world have adopted the higher voltage levels.

0ater it was observed that the impact of such high voltage levels on the

environment needed careful attention because the use of high surface voltage

gradients on conductors led to the interference problems from powerfre!uency to

T$ fre!uencies. Thus corona effects,electrostatic fields in the line vicinity,

losses,audible noise, carrier interference and radio interference became recogni/ed

as steadystate problems which governs the line conductor design, line height, and phase-spacing used to eep the interfering fields within prescribed limits."se of 

synchronous condensers due to high line charging currents at load end only became

impractical to control voltages at the sending-end and receiving-end

 buses."se of hunt compensating reactors for voltage control at no load and

switched capacitors at load conditions became necessary.. 'll these are still

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categori/ed as steady-state problems.However, the single major problem

considered with e.h.v. voltagelevels is the overvoltages during switching

operations which is commonly nown as switching-surge

overvoltages.

1.1 ROLE OF EHV AC TRANSMISSION

Industrial-minded countries of the world re!uire a vast amount of energy of which

electrical energy forms a major fraction. There are other types of energy such as oil

for transportation and industry, natural gas for domestic and industrial

consumption, which form a considerable proportion of the total energy

consumption. Thus, electrical energy does not represent the only form in which

energy is consumed but an important part nevertheless. It is only 12+ years since

the invention of the dynamo by 3araday and 14+ years since the installation of thefirst central station by #dison using dc. 5ut the world has already consumed major 

 portion of its natural resources in this short period and is looing for sources of 

energy other than hydro and thermal to cater for the rapid rate of consumption

which is outpacing the discovery of new resources. This will not slow down with

time and therefore there exists a need to reduce the rate of annual increase in

energy consumption by any intelligent society if resources have to be preserved for 

 posterity. 'fter the end of the econd 6orld 6ar, countries all over the world

have become independent and are showing a tremendous rate of industrial

development, mostly on the lines of 7orth-'merican and #uropean countries, the"...8. and 9apan. Therefore, the need for energy is very urgent in these

developing countries, and national policies and their relation to other countries are

sometimes based on energy re!uirements, chiefly nuclear. Hydro-electric and coal

or oil-fired stations are located very far from load centres for various reasons

which re!uires the transmission of the generated electric power over very long

distances. This re!uires very high voltages for transmission. The very rapid strides

taen by development of dc transmission since 1:2+ is playing a major role in

extra-long-distance transmission, complementing or supplementing e.h.v. ac

transmission. They have their roles to play and a country must mae intelligent

assessment of both in order to decide which is best suited for the country;seconomy. This boo concerns itself with problems of e.h.v. ac transmission only.

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  CHAPTER II. DESIGN METHODOLOGY

3ig 1<#.H.$ Tower 

3ollowing parameters should be carefully considered while designing a #.H.$ ac

transmission line.

• (ollecting preliminary line design data and

gathering available climatic data.

• electing 8eliability level.• (alculating climatic loading on components.

• (alculating loads corresponding to security

re!uirements.

• (alculating loads according to safety

re!uirements.

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• electing appropriate correction factors.

• =esigning the components for the above load

and strengths.

2.1 A. Reliability Levels• 8eliability 0evel ≥ 1

• Higher the 8eliability higher is the safety

factor and hence, more is the cost.

2.2 . Sele!ti"# "$ T%a#s&issi"# V"lta'e

• tandard voltage >>,11+,1)4,44+,++ ?$

• election criterion of #conomic $oltage

1. @uantum of power is evaluated

4. 0ength of line). $oltage regulation

. Aower loss in transmission

2. Initial and operating cost

 2.( C. E!"#"&i! V"lta'e "$ T%a#s&issi"#

"$ P")e%

# B 5.5 √(km/1.61+(load in kva)/150)Table 1* E!"#"&i! V"lta'e "$ 

T%a#s&issi"# "$ P")e%

#(C7CMI( $C0T'D#

=8CA

=IT'7(#%miles&

E>2$ 411>

2++$ 11)

)2$ 2:1+

 2.+ D. Ty,es "$ T")e%s

• Type ' Tower <

Tangent tower with suspension string• Type 5 Tower 

mall angle tower with tension string

• Type ( Tower 

Medium angle tower with tension

string

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• Type = Tower 

0arge angle tower with tension string

• Type # Tower 

=ead end tower with tension string

•pecial Tower 

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3ig < Tower tructure

 2.- E. Sele!ti"# "$ T")e% St%!t%e

• ingle circuit towerF=ouble circuittower 

• 0ength of insulator assembly

• Minimum clearances between ground

conductors,and between conductors

and ground

• 0ocation of ground wires with respect

to outermost conductor 

• Minimum clearance of the lowest

conductor above ground level

 2./ 0. Sele!ti"# "$ C"#!t"% Sie

• Mechanical 8e!uirement

• #lectrical 8e!uirement

1. Mechanical 8e!uirement

• Tensile strength%for tension&

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• train strength%for vibration&

4. #lectrical 8e!uirement

• (ontinuous current rating

• hort time current carrying rating

• $oltage drop• Aower loss

• 0ength of line

• (harging current

2.3 G. I#slat"% Re4i%e&e#t

Insulators are used to support line

conductor and it also provides clearance

from ground and structure.

Insulator material are as followsG

• Toughened glass• 3iber class

• High grade electric porcelain

Types of Insulators are categori/ed as G

• =isc type

• Strut type

• on! rod in"ulator

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  CHAPTER III. PROLEMS ENCOUNTERED

The problems encountered while using such high voltages are different from those

encountered at lower voltages. These problems are<

%a& Increase in (urrent =ensity due to increase in line loading by using series

capacitors.

%b& "se of bundled conductors.

%c& High surface voltage gradient on conductors.

%d& (orona problems< 'udible 7oise, 8adio Interference, (orona #nergy 0oss,

(arrier Interference, and T$ Interference.

%e& High electrostatic field under the line.%f& witching urge Cvervoltages which cause more havoc to air-gap insulation

than lightning or power fre!uency voltages.

%g& Increased hort-(ircuit currents and possibility of ferro resonance conditions.

%h& "se of gapless metal-oxide arresters which replaces the conventional gap-type

ilicon (arbide arresters, for both lightning and switching-surge duty.

%i& hunt reactor compensation and use of series capcitors, resulting in possible

subsynchronous resonance conditions and high shortcircuit currents.

%j& Insulation coordination based upon switching impulse levels.

%& ingle-pole reclosing to improve stability, but causing problems with arcing.

(.1 A. Ove%v"lta'es

Cvervoltages in #H$ systems are caused by switching operations.overvoltages due

to the release of internally trapped electromagnetic and electrostatic energy in an

e.h.v. system which can further cause serious damages to the e!uipment

insulation.These damages could, under many circumstances, be more severe than

lightning damage.Therefore,urge diverters and resistances are included purposely

while maing switching operations as well as other schemes to reduce the danger 

to a considerable extent. Investigation of switching overvoltages has ac!uired

very great importance since the transmission voltages are on the increase and linelengths and capacity of generating stations are also increased. It is assumed that the

short-circuit capacity of sources is mainly responsible for a large amount of 

damage to the insulation.

(.2 . Li'5t#i#' St%"6es T" Li#es

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0ightning is considered as one of the major source of danger and damage to e.h.v.

transmission lines, resulting in the loss of transmission up to a few hours to

complete destruction of a line. This entails a lot of expense to power utilities and

consumers.0ightning protection methods are based on sound scientific and

engineering principles and practiceGhowever, extensive damages do tae place in

 power systems in spite of this.Thus,no transmission line design can be considered

lightning-proof, nor do designers aim for this goal. 0ine outages, or a line being

taen out of service for a short time,and line designs against these are based on

statistical procedures. 'n acceptable design would be to allow a certain number 7t

outages per year per 1++ m of line, or other time durations and other line lengths.

The possibility of an outage depends on so many factors which are statistical in

nature that a worstcase design is neither practical nor economical.It is evident that

the number of stroes contacting a tower or ground wire along the span can

only depend on the number of thunderstorm days in a year called the ;eraunic

level; or also called ;isoeraunic level;, and denoted by Il. Cn the basis of a vastamount of experience from all over the world, it is estimated that the number of 

lightning stroes occurring over 1 s!. m. per year at any location is fairly well

given by

#s7 st%"6es t" ea%t586&2 9 yea% 7 :;.1- t" ;.2<I6l

The actual factor must therefore be determined from observational data in any

given region. 'lso, from experience, the area intercepted by a line with its

metallic structures is taen to be proportional to

%a& %height of tower, ht 4 height of 

ground wire at mid span, hg& and

%b& the distance sg between ground wires if 

there is more than 1 ground wire on the tower. (ombining all these factors, it is

estimated that the number of stroes intercepted by 1++ m of line per year is

given by

 7s B %+.12 to +.4& Il J+.+1)) %ht 4 hg&

1.1 sgK with hg,and sg in metres.

 

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  CHAPTER IV. PROTECTION MEASURES

everal measures are being taen to overcomes theproblems faced while using

#.H.$ ac transmission line.

0ightning arresters which are also called ;surge absorbers; because they are also

meant for switching surge protection.Their purpose is to protect primarily the

major e!uipment such as transformers, rotating machines,shunt reactors, and even

entire substations. 0ess expensive protective devices such as rod gaps can be used

for protection of transformer and circuitbreaer bushings and open contacts.6hen

substations are to be protected,they are located at the entrance of the incoming andoutgoing lines.Modern surge absorbers re!uired for e.h.v. levels are designed to

offer protection to the e!uipments and lines for both lightning overvoltages and

currents as well as switching surge over-voltages where the energy involved is

much higher.'rresters can be classified into three important types and categorised

according to their internal structure.They are G

%1& Dap type arrester without current-limiting functions.

%4& Dap type arrester with current-limiting capability.

%)& Dapless metal oxide varistors. The Dap type arrester is commonly nown by

different names such as Thyrite, Magnavalve, 'utovalve,Miurite.The non-linear

resistance material is usually sintered ilicon-(arbide %i(& and is designed to

dissipate the energy in short duration lightning-stroe current and the current at

 power fre!uency that will follow this current when the series gap conducts.The

current is then finally interrupted at a power-fre!uency /ero.The second type of

arrester nown as the current-limiting gap type, is the one in which a magnetic

action on the arc between the gap establishes a lengthening of the arc withconse!uent large resistance which is capable of limiting the current.In such type of

design,the power-fre!uency current can be extinguished before it reaches a current

/ero.uch an arrester can perform switching surge function also.The non-linear

resistance is still i(.

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The third and the last one,the gapless MC$,is designed for low-voltage low-current

electronic circuitary but recently it is sufficiently well developed to fulfill the e.h.v.

re!uirements.

  CHAPTER V. E.H.V Testi#' a# Te!5#"l"'y Use

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'll the e.h.v. e!uipment voltage levels are governed by tandard

specification.#!uipment manufacturers produce goods not only meant for domestic

use but also for export so that a design or testing engineer must be familiar withthese specifications from all over theworld.ome of the major specifications are

I.#.(., I..I., $.=.#., .'.#., '.7..I., 5..., (..'.., 9apan and others.

-.1 Te!5#"l"'y se i# EHV AC t%a#s&issi"#*

3'(T technologies have a small footprint and minimal impact on the

environment. Aroject implementation times are considerably faster and investment

costs substantially lower than the alternative of building more transmission lines or new power generation facilities.

3'(T consists of three technology branches<

• series compensation

• dynamic shunt compensation

• dynamic energy storage

-.2 Se%ies !"&,e#sati"#< eries compensation was invented by '55 in 1:2+. It

made possible the world;s first ++ $ transmission in the 1:2+s by resolving the

issue of how to transmit power over long distances.

 

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&i! 5' Serie" ompen"ation

 *e ene,t" o- "erie" ompen"ation improved "y"tem "taility

inrea"ed tran"mi""ion apaity and redued overall poer

lo""e".

" tran"mi""ion apaitie" ro"e "o did t*e need -or *i!*er

"erie" ompen"ation volta!e".

ontrollale "erie" ompen"ation a" in"talled y in t*e

late 1%%0" and i" al"o part o- t*e &S -amily.

-.( SVC Li'5t*

In 1::*, '55 launched a new generation of dynamic shunt compensation

technology for transmission, steel and rail applications - $( 0ight.

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  3ig >< $( 0ight

SVC Li'5t )it5 E#e%'y St"%a'e*

The integration of dynamic energy storage into transmission and distribution

systems has the potential.

The new technology is based on $( 0ight, combined with 0i-ion battery

storage.

CHAPTER VI. MERITS AND DEMERITS O0 E.H.V

AC TRANSMISSION LINE

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A. Me%its

• 8eduction in the (urrent

• 8eduction in the losses• 8eduction of the conductor material re!uired

• 8eduction in voltage drop

• Improvement of voltage regulation

• Increase in Transmission fre!uency

• Increased power handling capability

• The total line cost per M6 per m decreases considerably with the increase

in line voltage

. De&e%its

• (orona loss and 8adio interference

• 0ine supports

• #rection difficulties

• Insulation needs

• The cost of transformers,switch gear 

e!uipments and protective e!uipmentsincreases with increase in transmission line

voltage

• The #H$ lines generate electrostatic effects

which are harmful to human beings and animals

 

CHAPTER VII. CONCLUSION AND 0UTURE

=OR> 

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In this article,we have outlined the design methodology of #H$ ac transmission

lines including the various factors re!uired for their designs.This paper also

 presents the problems encountered while using #H$ ac transmission line and it

 presents the various techni!ues adopted to overcome these problems.#H$

transmission lines uses #H$ cables which are used for high voltages and power when necessary.The future wor where #H$ ac transmission will prove effective

follows<

• upport is going for a national #H$ interstate transmission grid

• 3or "H$,fewer lines would be needed and for voltage above E>2 $

more lines would be needed.

• It is understood,however,that the completion of this grid re!uires

collaboration among staeholders,especially transmission owners

and operators.

  RE0ERENCES

• www.rcerooree.inFpdfFpdfoFT##+)).pdf 

• http<FFwww.ijert.orgFview-pdfF4)EFa-survey-paper-on-extra-high-voltage-

ac-transmission-lines

• https<FFboos.google.co.inFboosFaboutF#xtraLHighL$oltageL'L(LTransmis

sionL#ngi.htmlidBe437d$4'ro(.

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• #lectric Aower 8esearch Institute. 1:*4.Transmission 0ine econd #dition.

• 5onneville Aower 'dministration. 1:EE. =escription of #!uations and

(omputer Arogram for Aredicting 'udible 7oise, 8adio Interference,

Television Interference, and C/one from '-( Transmission 0ines. Technical

8eport #89-EE-1>E.• (.0 6adhwa< #lectrical power systems, fifth edition. 8aosh =as

5egumudre< #xtra High $oltge '( Transmission #ngineering.

1#