Whether in infrastructure systems, industry or households, transformers always play a key role in the reliable transmission and distribution of power. The construction, rated power, volta…Descripción completa
power transformer designFull description
Descripción: Whether in infrastructure systems, industry or households, transformers always play a key role in the reliable transmission and distribution of power. The construction, rated power, voltage leve...
Transformer tests
Its testing of Power transformers ABB and its very useful.
Full description
Its testing of Power transformers ABB and its very useful.
This article is limited in scope to standard testing procedures for transformers prior to installation, with their general purpose and methodology.
Full description
Electrical Engineering
Transformer tests
Descrição: Its testing of Power transformers ABB and its very useful.
Its testing of Power transformers ABB and its very useful.
Descripción: Transformer tests
Transformer tests
Transformer tests
Electrical Engineering
For BSNL LDCEFull description
Descripción: Working Group A2.36
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EARTHING TRANSFORMERS FOR POWER SYSTEMS
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ABSTRACT:-
Normally power systems and net works are operated under variable omple! stresses."n power systems t#e $aults are not avodable even a$ter taking utmost are at every stage$rom planning to maintainane. T#e grounding o$ a iruit redues potential stresses under $ault ondition. %ower $eeding $rom delta delta or i$ t#ere is no aessibility $or star onneted trans$ormers oasionally s#orted to ground is very ommon-un-intentional grounding ours any w#ere $rom t#e $eeding system to utili&ation e'uipment T#e main ob(etive o$ grounding neutral is to make a s#ort iruit urrent su$$iient in magnitude $or t#e relay ation. T#is artile restrited to &ig-&ag type wit# oil $illed trans$ormers. T#e neutral point is usually available at every voltage level $rom generator to trans$ormers. "n t#e absene o$ a power trans$ormer o$ suitable apaity) onnetion and design a separate grounding trans$ormer an be used . T#ey are indutive devies intended primarily to provide a neutral point $or grounding purpose. T#e main purpose o$ t#is paper is to disuss about t#e di$$erene between *art#ing trans$ormer and %ower trans$ormer and to disuss about t#e designing o$ eart# trans$ormers.
"NTR+,UCT"+N:A trans$ormer is a devie w#i# eletromagnetially trans$ers A.C. voltage $rom one level to anot#er level. An eart#ing trans$ormer is a trans$ormer primarily to provide a neutral point $or grounding purpose. T#e sole duty o$ t#e grounding trans$ormer is to pass ground urrent during an eart# $ault.) and it arries no use$ul load. T#e desirable 'uantities o$ an eart#ing trans$ormer are low &ero impedane and low losses no load losses. www.Uandistar.org
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/UNCT"+N +/ *ART0"N1 TRANS/+R2*RS:•
Apart $rom providing an easy pat# to ground urrent during an eart# $ault) t#e $ollowing additional $untions are also to be a#ieved
•
0olding t#e neutral s#i$t wit# in t#e limits
•
%ermitting t#e irulation o$ unbalaned load urrent in t#e neutral
•
To limit t#e urrent during line to eart# $aults
•
To eart# t#e system
•
To provide single p#ase line to neutral load
•
Can be used wit# resistane 3reatane3ar suppression oil
C+2%AR"S"+N
B*T4**N
*ART0"N1
AN,
%+4*R
TRANS/+R2*RS:T#e seletion any trans$ormer mainly by two $ators-namely) primary voltage and load ./or an eart#ing trans$ormer load is s#ort time or s#ort duty only at t#e time o$ $ault )normally $rom a $ew seonds to one minute COMPARISION CHARACTERISTICS 2.29MVA (S.C) 6.6KV 600 Amps(ET@)
*T5
2MVA110.!""KV #$%& 1 (PT@)
%T5
%urpose
To provide a neutral point Raiding $or eart#ing voltages
67A rating
S#ort time
Continuous
7oltages in general
Up to 88kv
0ig#er voltageseven 9967 and above
No o$ windings
+ne3two
+ne3two3t#ree
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or
lowering
www.Uandistar.org ,iretion o$ power $low
Uni diretion
B"-diretional
S.C wit# stand duration
;se.to ; min
9 se
No load losses
No load losses and load losses
2agneti&ing urrent
7ery less
Normal
%riority $or impedane
=ero se'uene impedane
S#ort iruit impedane
S#ort iruit urrent
,epends on system $rom Up to 9> times normal $ew #undred amperes to $ew urrent t#ousand amperes
Type o$ voltage mi!ed
Constantin general
Constant3variable3regulation
Transportation
Road
Road3Rail
S#ort iruit temperature "n degrees entigrade
9>
9>
0armoni residuals
$ree
e!ist
0ig#
"nsulation
Uni$orm
Uni$orm3graded
*$$iieny
2ore
Cost
2ore
•
4eig#ts) losses) dimensions and ost $ators are mu# lower.
•
Rise o$ oil 3winding temperature is very less.
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0ig#er spei$i loading and e$$iieny.
•
2ore signi$iant $ator is &ero se'uene impedane.
Significance of zero sequence parameters "n symmetrial omponents t#e positive se'uene is one #aving normal p#ase se'uene? t#e seond is o$ negative se'uene wit# reversed p#ase se'uene? and t#e t#ird t#at #as no se'uene and is alled &ero se'uene @ are important parameters. An eart# $ault is one t#at part o$ t#e urrent in t#e $aulty p#ase returns to t#e supply t#roug# t#e eart#. T#is is due to a symmetrial omponent onsisting o$ t#ree single p#ase urrents - one in ea# line) and all being in p#ase. "n general) t#e impedane o$ t#e trans$ormer is t#e main $ator w#i# in$luenes appliations. T#e &ero se'uene impedane o$ a standard eart#ing trans$ormer an be alulated $rom t#e $ollowing $ormula: 8* =s "n 4#ere =s"mpedane in o#ms 3 p#ase *
www.Uandistar.org negative impedanes. A &ero se'uene reatane is e'ual to or less t#an a positive se'uene and it depends on t#e $orm o$ ore onstrution and disposition o$ t#e windings W'$ %*+,-%%*-*/ s+ %/% s p+*3*++*/ 4
T#e purpose to establis# a suitable ground pat# an be a#ieved wit# t#e #elp o$ t#ree pairs o$ onentri oils onneted to oppose ampere turns. As t#e $lu!es oppose) t#e trans$ormer takes a very small magneti&ing urrent during normal ondition.
4inding #as mu# lower impedane to &ero se'uene urrents.
•
/ree $orm #armoni residuals.
•
Stable neutral an be obtained.
•
2ost eonomial and pratial.
•
Can be used wit# t#ree p#ase system wit#out seondary winding.
•
%ermitting single p#ase line to neutral.
•
Can be eonomially used wit# resistane3reatane3are suppression oil.
•
*'uivalent 67A is appro!imately >D.>E o$ star-delta trans$ormer.
•
Avoidane o$ undesirable stresses in t#e insulation.
•
Can be used wit# eit#er delta or star onneted winding to $eed desired load.
•
"t keeps &ero se'uene impedane onstant even w#en au!iliary winding under load.
•
/ault urrent is not re$leted on to t#e seondary side au!iliary winding.
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www.Uandistar.org /rom t#e above) it is very lear t#at t#e inter-onneted star winding an be utili&ed eit#er as an eart#ing trans$ormer or power trans$ormer) or in ombination @ depending upon t#e re'uirement. R% %/ s %*+,+*&*/ p+m**+s 3 % *+'% +%s3+m*+
T#e eart#ing trans$ormer is o$ s#ort time rating ; seonds to ; minute. T#e rating o$ an eart#ing trans$ormer is entirely di$$erent $rom t#at o$ a power trans$ormer. %ower trans$ormers are designed to arry total load ontinuously) w#ilst an eart#ing trans$ormer arries no load) and supplies urrent only i$ one o$ t#e lines beomes grounded. "t is usual to spei$y t#e single p#ase eart# $ault urrent) t#at t#e eart#ing trans$ormer must arry $or su$$iient time. Sine it is almost working on no-load) ditates to #ave low iron losses. Beause o$ it being a s#ort time devie) its si&e and ost are less t#an t#at o$ a ontinuous duty trans$ormer o$ e'ual 67A rating. T#e 67A rating o$ a t#ree p#ase eart#ing trans$ormer or a bank is t#e produt o$ normal line to neutral voltage 67 and t#e neutral or ground amperes t#at t#e trans$ormer is designed to arry under $ault onditions $or a spei$ied time. T#e total eart# $ault urrent and 7 t#e line voltage) t#e eart#ing trans$ormer s#ort time rating is e'ual to 87".
v/√3 v/√3 v/√3
Three phase inter connected star neutral earthing transformer
1. V&*5, T#e line-to-line voltage o$ t#e system. 2. C++*%5,T#e ma!imum neutral urrent to
arry $or a spei$ied duration. "n a
grounded system it is based on t#e type o$ grounding. ,epending on t#eir duration) several rates o$ s#ort ". Tm*5,,esigned
to arry rated urrent $or a s#ort time duration i.e.) ;
seonds to F seonds .,epending upon t#e time setting o$ t#e protetive gear on t#e system) And t#e loation o$ t#e trans$ormer .*art#ing trans$ormer time is ; se $or protetion) and $or $eeder it " F se. !. R*-%-*5, t#is
'uantity is a $untion o$ t#e initial symmetrial t#ree p#ase
s#ort iruit 67A. "t is also based on t#e type o$ grounding) and type o$ appliation o$ lig#tning arrester and transient over voltages.
T#e desired eletrial parameters o$ t#e eart#ing trans$ormer are to be a#ieved by veri$ying t#e alulations based on eletrial) me#anial and t#ermal omputations. Su# as t#e re'uired eletrial strengt#) me#anial ruggedness) dynami and t#ermal resistane o$ t#e windings in t#e event o$ s#ort iruit) are to be Solved are$ully at t#e designed stage. w#en designed as an eart#ing trans$ormer it is Usually manu$atured as an auto trans$ormer inter-start.
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Schematic winding arrangement of interconnected star earthing transformer
T#e $ollowing brie$ details re$er to a ore type oil $illed trans$ormer wit# ylindrial windings $or &ig-&ag-wit# or wit#out au!iliary winding-w#i# are popular all over t#e world. T#e ore o$ su# a trans$ormer is built in t#e same manner as t#at o$ a www.Uandistar.org
www.Uandistar.org trans$ormer @t#e only di$$erene is t#at instead o$ two windings per limb w#i# is divided into two e'ual portions) and onneted as s#own in $igure. T#e urrents $lowing are in opposition) t#ere by undesirable #armonis are avoided. T#e #oie o$ t#e winding on$igurations are ditated by &ero se'uene impedane in a single winding .wit# an au!iliary by bot# &ero se'uene and s#ort iruit impedane. Au!iliary winding may be used ontinuously to supply station au!ilaries. T#e type o$ windings may be
eit#er multilayer #elial or dis windings mainly based on
urrent and voltages .generally) voltages o$ t#ese trans$ormers are up to 88 67 and urrents up to several kilo amps based on system re'uirements . figure-3
s#ows di$$erent on$igurations .$igure-8bG8are re'uired to meet bot# &ero se'uene impedane and s#ort iruit impedane .magneti and eletri loadings are similar to t#at o$ a power trans$ormer .t#e basis $or intimate temperature rise alulation is t#at all t#e #eat is stored in t#e opper wit#out dissipation to insulating media or surroundings .aording to standards )t#e end temperature rise depends on t#e duration o$ t#e $ault t#e ultimate being 9> $or a opper winding in oil .$or ontinuous rating t#e alulation is similar to t#at o$ a normal power trans$ormer .insulation design is mainly based on deletri onstants o$ paper and oil .t#e ideal stress distribution an be obtained t#roug# $ield plotting by t#e $inite element met#od .beause o$ t#e $re'uent s#ort iruit apability) remedial measures like strengt#ening o$ t#e oils) proper materials) and www.Uandistar.org
www.Uandistar.org avoidane o$ magneti asymmetry are to be observed. Sine only iron losses are to be dissipated) t#e tank dissipation is ade'uate in a ma(ority o$ t#e ases wit# au!iliary loading proper are is neessary in respet o$ #eat dissipation $or t#e reliability o$ t#e trans$ormer. "n ase o$ eart#ing trans$ormers $or industrial appliations and $or #eavily polluted atmosp#ere t#e demand is $or bus#ings o$ #ig#er reep age distanes to avoid $re'uent $las#overs. /urt#ers) t#e e!ternal sur$aes are to be painted wit# epo!y base paint .testing o$ t#ese trans$ormers are in aordane wit# national and international standards to veri$y various parameters. And) transportation o$ t#ese trans$ormers are similar to small power trans$ormers.
C%-&s%5,
T#roug# t#e eart#ing trans$ormers are o$ smaller ratings ompared to normal power and *07 trans$ormers t#ese are very ritial e'uipments in utility and industrial appliations. T#eir $ault urrents are di$$erent $or di$$erent installations. Comparison o$ t#ese industrial trans$ormers are to be are$ully di$$erentiated. A deep study is re'uired $or di$$erent eart#ing met#ods) and $or oordination o$ t#e system e'uipments $or reliable operation. /urt#er resear# study on a distribution trans$ormer wit# out ma(or modi$iation o$ t#eir eletrial parameters is desired. 4#en geomagneti $ield disturbanes aused by ,C indued urrents enter power system at grounded neutral) t#ese are to be are$ully evaluated in omparison wit# line to eart# $ault urrents. R*3*+*%-*5
