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High Voltage Lectures-dr Ali Albakry

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   High Voltage Engineering By  Al-Mussaib Technical College / Elec. Depart. / Fourth Class Dr. Ali Albakry HIGH VOLTAGE ENGINEERING  By  Dr. Ali A. Albakry  Al - Mussaib Technical College o Engineering For  Fourth Class  Depart!ent o Electrical o#er Techni$ues Engineering   Main %eerences &-'High Voltage Engineering()by E. *uel an+ M. Ab+ullah.,-'Electric o#er yste!s() by B. M. ee+y.-'High Voltage Technology() by B. Alston.0-'Electric o#er yste!s() 1ol.,) by A. E. 2uil an+ eterson. 1    High Voltage Engineering By  Al-Mussaib Technical College / Elec. Depart. / Fourth Class Dr. Ali Albakry  3ecture '&(&.& 4ntro+uction In the initial stages D.C was used for electric ower trans!ission. This was due to two i!ortant reasons #$Ease of control%$D.C !otors were the onl& electro$!echanical energ& con'erters.Howe'er with the introduction of transfor!ers in #((# and the three hase s&ste!s in #((() the o*'ious ad'antages of alternating current co!*ined with the successful alication of associated e+ui!ents soon aears to *e !ore econo!ical.Electrical ower !a& *e trans!itted using high and e,tra 'oltages. The ter! e,tra high 'oltage -EHV has generall& acceted to descri*e the s&ste!s of %/0 1V u to 234 1V and for the 'oltage a*o'e 234 1V) the ter! 5ltra High Voltages -5HV is alied) while the 'oltage the *elow %/0 1V na!ed High Voltage -HV. #.% Ad'antage and Disad'antage of using HV &.,.& A+1antage o using High Voltage in trans!ission an+ +istribution syste!s 5 #$ To trans!it certain ower o'er certain distance) the conductor 'olu!e will *e less under high 'oltage condition as follow  V c  6 -7 #  L %  8   9 7 %  . -#9 -V % cos % :;here L length of the line.V hase 'oltage.7 # ower trans!itted 9 hase.7 % ower loss 9 hase.cos : 6 ower factor. 2    High Voltage Engineering By  Al-Mussaib Technical College / Elec. Depart. / Fourth Class Dr. Ali Albakry ,- %egulation The regulation !a& *e defied as the ercentage 'ariationof recei'ing end 'oltage when the sending end 'oltage constant. Trans!ission lines suffer fro! inherent 'oltage 'ariations at the recei'ing end with changes in loads< howe'er the 'oltage 'ariations are undesira*le) where the regulation of the line !a& *e gi'en *&  Reg = 6 --7.R > ?.@ 9 V % res    =;here R and ? are resistance and reactance of line) V res is the recei'ing 'oltage of the line. 7 and @ are the real and i!aginar& ower.ro! the a*o'e e+uation one can see that< the regulation is in'ersel& roortional with the s+uare of the recei'ing end 'oltage./$ The ower trans!ission caacit& of a trans!ission line is roortional to the s+uare of the oeration 'oltage) *ut the trans!ission line and ter!inal e+ui!ents costs are also increases with an& increase of 'oltage. As a conse+uence the o'erall caital cost of trans!ission decreases as a 'oltage increases. &.,., Disa+1antages o using H.V in trans!ission an+ +istribution electrical syste!s5  #$ Due to the 'oltage stress at the surface of a conductor in air) discharges occur if this stress e,ceeds a critical 'alue. These discharges gi'e rise to ower loss fro! the conductor and also ro'ide a source of interference with radio co!!unication. It can *e shown that the 'oltage stress at the surface conductor is gi'en -aro,i!atel& as 3    High Voltage Engineering By  Al-Mussaib Technical College / Elec. Depart. / Fourth Class Dr. Ali Albakry  E !a, 6 V 9 - r. log -D9r r!s 1V 9 !;here r radius of conductors in !eters. D distance *etween conductors.B& increasing r) the 'alue of E !a, is reduced. or this urose the hollow conductors can *e used *ut *oth e,ensi'e in !anufacture and difficult to erect. Conse+uentl& the usual solution is to increase the nu!*er of the conductors er hase -*undle conductors. A further ad'antage of *undle conductors is that< the& are !ore fle,i*le and easier to handle than a single conductor or e+ui'alent cross section.  ,( 4nsulation 3e1el  The le'el of insulation re+uired on a H.V Trans!ission Line-TL is deter!ined *& the !agnitude of the 'oltage surgeswhich are liel& to occur. These surges can *e internall& generated *& switching) or the& can *e e,ternall& induced due to at!osheric cause -lighting.To withstand these surges the insulation !ust *e sufficient) *ut it is o*'iousl& unecono!ic to ro'ide against allcontingencies) conse+uentl&) e+ui!ent is designed to withstand 'oltages u to a certain 'alues called the I!ulse 'oltage le'el or Basic Insulation Le'el -BIL) and surge di'erters or sar gas are e!lo&ed to rotect the nor!al insulation against a*nor!al 'oltages. ( tability The e,ression for ower trans!itted *etween two ac s&ste!s is gi'en *&  7 6 -V  . V r / X) sin  4 
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