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Transcript of Transformers-Lec11.pptx
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Three Phase TransformersEE3003 Electrical Machines I
By:A.Paranietharan
Electrical Engineer
Ceylon Electricity Board
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Winding connections
Standard terminal maring of !" # $" %indings of 3Phase Transformer&
'ote: ( "oltage ind)ced in all %indings in a gi*en leg are in(+hase ,-eca)se all
are %o)nd in the same sense
There are three di/erent o+tions of connections&
Star
1 2elta
3 ig(4ag
A A1
B B1
C C1 c c1
- -1
a a1
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Winding connections . . .
. Star
A
A1
B
B1C
C1
"oltage Phasors 5 Star connection
A A1
B B1
C C1
'
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Winding connections . . .
1. 2elta
A
A1B
0
B1
C0
C1
"oltage Phasors 5 2elta connection
A A1
B B1
C C1
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Winding connections . . .
3. ig(4ag
A6
A3
B6
B3
C6
C3
"oltage Phasors 5 ig 4ag connection
C
C1
B
B1
A
A1
A A1
B B1
C C1
A3 A6
B3 B6
C3
C6
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Winding connections . . .
ig(4ag . . .*oltage %ise 4ig(4ag connection gi*es only 78.89 star
*oltage. !o%e*er& 4ig(4ag connection has *ery )sef)l
as+ects s)ch as for creating articial ne)tral +oint in an
isolated +art of a system ,e.g. Earthing transformer&
s)++ressing harmonics in case of harmonic rich loads ,Po%er
Electronic con*erter systems etc.
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Per +hase e;)i*alent circ)it
r5 Primary %inding resistance +er +hase
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"ector Sym-ol
The follo%ing shall -e s+ecied to identify a transformer in f)ll&. $ine *oltage ratio
1. M"A ca+acity
3. "ector sym-ol
e.g. 33? "& @M"A& 2y transformer
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"ector Sym-ol
"ector sym-ol has three +arts&
a ++ercase letter ,2& or signifying !" connection ,2elta&
Star or ig(4ag
- $o%ercase letter ,d& y or 4 signifying $" connection
c "ector n)m-er re+resenting the +hase shift of $" side line
*oltage %ith res+ect to !" side line *oltage
( standard *ector n)m-er is gi*en as the !o)r('o ass)ming
long hand ,min)te hand to -e at cloc +osition 1.
or e
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"ector Sym-ol . . .
Hour NoPhase shift of LV line voltage
w.r.t HV line voltage
0 0
8 70
( 30
D30
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"ector Sym-ol . . .
E.g.d
( !" side is in stard 5 $" side is in delta
5 $" line *oltage is 30 lagging !" line *oltage
If %e ha*e tertiary %inding too& the *ector sym-ol m)st contain its
information too.
E.g:y0d
( !" side is in star
y 5 $" side is in star
0 5 $" line *oltage in(+hase %ith !" line *oltage
d 5 tertiary in delta
5 tertiary line *oltage is 30 leading !" line *oltage
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Classes of 3 +hase transformers:
There are fo)r ,06 -asic classes&. Class transformers
1. Class 1 transformers
3. Class 3 transformers
6. Class 6 transformers
The -asis of classication is +hase shift ,of $" line *oltage %.r.t
!" line *oltage
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Classes of 3 +hase transformers . . .
Class transformers 0+hase shift
Class 1 transformers 70+hase shift
Class 3 transformers ( 30+hase shift
Class 6 transformers D 30+hase shift
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Winding Interconnections
Each %inding in a transformer is ins)lated to %or at some
*oltage rating and %e m)st ens)re that this rating is not
eect to this constraint %e can decide any
s)ita-le interconnection.
To +)t in a di/erent %ay %e can determine the
interconnection as +er the gi*en *ector sym-ol.
Some of these interconnections are ill)strated in the follo%ing
slides&
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Winding Interconnections . . .
Yy0A1
A
B1
BC
1
C
"ector 2iagram
a1
a
-1
-c1
c
a1 a
-1 -
c1 c
A A1
B B1
C C1
Terminal connectio
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Winding Interconnections . . .
Dd0
B
B1
C
C1
"ector 2iagram
A A1
B B1
C C1
a1 a
-1 -
c1 c
Terminal connection
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Winding Interconnections . . .
Yy6A1
A
B1
BC
1
C "ector 2iagram
a
a1
-
-1
c0
c1
a a1
- -1
c c1
A A1
B B1
C C1
Terminal connection
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Winding Interconnections . . .
Dy1
A0
A1
B0
B1
C0
C1
"ector 2iagram
a1 a
-1 -
c1 c
a1
a0
-1 -0
c1
c0
A A1
B B1
C C1
Terminal connectio
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Winding Interconnections . . .
Dy11
A1
A0
B1
B0
C1
C0
"ector 2iagram
a1
a0
-1
-0
c1
c0
a1 a
-1 -
c1 c
Terminal connection
A A1
B B1
C C1
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Winding Interconnections . . .
Dz0
"ector 2iagram
A1
A0
a6
a3
c6
c3
c0
c1a1
a6 a3
-6 -3
c6 c3
a1 a
-1
-
c1 c
A A1
B B1
C C1
Terminalconnection
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Winding Interconnections . . .
i. Zy1
ii. Zy11
iii.Yd11
iv.Yd1
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E/ects of %rong +olarity connectionWhen connecting transformer terminals es+ecially +olarity
connections& %e
sho)ld not mae errors& the conse;)ences may -e either fatal to
the
transformer or )ne
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E/ects of %rong +olarity connection . . .
A1
A
B1
BC
1
C
a1
a
-1
-0
c1
c0
a1 a
-1 -
c c1
A A1
B B1
C C1
Erroneo)s connection %ith$" %inding cc1 connected%ith %rong +olarity
It res)lts& )n-alanced3+hase $" o)t+)t.Also +hase shiftamong 3 +hases are)n-alanced.
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E
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Magneti4ation -eha*io)r of 3 +hase transformers
Magneti4ation:
To magneti4e a transformer means to set magnetic F)< in its iron
core.
Ty+ical Magneti4ation C)r*e
The iron core has a non(linear magnetic -eha*io)r # this leads to
either non(linear magneti4ing c)rrent or non(linear magnetic F)
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Magneti4ation -eha*io)r of 3 +hase transformers . . .If the a++lied *oltage is sin)soidal then the ind)ced emf and
hence F)< %ill -e sin)soidal. 'on(linear Im?-eha*io)r then
res)lts in a non(sin)soidal Im. i.e. !armonic rich Im. The dominant
is third harmonic c)rrent.
Im
Im
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Magneti4ation -eha*io)r of 3 +hase transformers . . .
The gra+h in red sho%s magneti4ing c)rrent containing a
signicant amo)nt of 3rdharmonic com+onent can -e as
high as 109 of f)ndamental com+onent.
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Magneti4ation -eha*io)r of 3 +hase transformers . . .
Gn the other hand& if magneti4ing c)rrent Imis sin)soidal the
res)lting F)< %ill contain harmonics
l)< %a*eforms -ecomes some%hat Fat(to+ %a*eforms
containing 3rdharmonics.
Im
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Magneti4ation -eha*io)r of 3 +hase transformers . . .
This harmonic rich c)rrent or F)< can inF)ence the
o+eration of a three +hase transformer. !armonic F)