Transformer protection 20.ppt
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1 > Transformer Protection
TRANSFORMER PROTECTION
Target Audiance
•Electrical Engineers
•Protection Engineers
•Test & Commissioning Engineers
•Power System Engineers
•Utility Engineers
•Electrical Technicians
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TRANSFORMER PROTECTION
Introduction
Transformers are acritical and expensive
component of thepower system !ue tolong lead time forrepair and replacementof transformers" ama#or goal oftransformer protectionis limiting the damageto a faultedtransformer Thecomprehensivetransformer protectionprovided $y multiplefunction protectiverelays is appropriate forcritical transformers ofall applications
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TRANSFORMER PROTECTION
The type of protectionfor the transformersvaries depending onthe application and
importance of thetransformerTransformers areprotected primarilyagainst faults andoverloads The type ofprotection used shouldminimi%e the time ofdisconnection for faultswithin the transformerand to reduce the risof catastrophic failureto simplify eventualrepair
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TRANSFORMER PROTECTION
Any extendedoperation of thetransformer under
a$normal conditionsuch as faults oroverloadscompromises the lifeof the transformer"which means
ade'uate protectionshould $e providedfor 'uicer isolationof the transformerunder such condition
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The various possible transformer faults are,
1. Overheating
2. Winding faults
3. Open circuits
4. External faults
. Over fluxing
TYPES OF FAULTS
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The! are due to
"ustained overloads and short circuits
#ailure of cooling s!stem
$rotection
The thermal overload rela!s and temperature rela!s, sounding
the alarm are used
The thermocouples or resistance temperature indicators arealso provided near the %inding.
These are connected in a bridge circuits.
When the bridge balance gets disturbed for more than the
permissible duration circuit brea&er trips.
OVERHEATING
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The %inding faults are called internal faults. The overheating or
mechanical shoc&s deteriorates the %inding insulation. 'f the%inding insulation(is %ea&, there is a possibilit! of
$hase to phase faults
Earth faults
'nter turn faults
$ersistent fault %ould have a possibilit! of oil(fire.
$)OTE*T'O+
ifferential protection
Over current protection is also used as a bac&up protection
#or earth fault protection, the restricted earth fault protection
s!stem, neutral current rela!s or lea&age to frame protection
s!stem is used.
WINDING FAULTS
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The open circuit in one of the three phases causes the
undesirable heating of the transformer.
Open circuits are much harmless compared to other faults.
Transformers can be manuall! disconnected from the s!stem
during such faults.
OPEN CIRCUIT
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Through faults are the external faults %hich occur outside the
protected -one.
These are not detected b! the differential protection.
'f faults persists the transformer gets subected to thermal and
mechanical stresses %hich can damage the transformer.
$)OTE*T'O+
The overcurrent rela!s %ith undervoltage bloc&ing, -erose/uence protection and negative se/uence protection are
used to give protection
The setting of the overcurrent protection not onl! protects
transformer but also covers the station busbar and portion of a
transmission line.
THROUGH FAULTS
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The flux densit! in the transformer core is proportional to the
ratio of the voltage to fre/uenc! i.e. 0f
Transformers are designed to %or& %ith certain value of fluxdensit! in the core. 'n the generator transformer unit, if full
excitation is applied before generator reaches its s!nchronous
speed then due to high 0f the overfluxing of core ma! occur.
$)OTE*T'O+
0f rela! called voltshert- rela! is provided to give the
protection against overfluxing operation.
OVERFLUXING
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Other faults
Tap changer faults
igh voltage surges due to lightning
"%itching surges
'ncipient faults
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Importance of Protecton
etect and isolate fault
aintain s!stem stabilit!
To limit the damage in adacent e/uipment
inimi-e fire ris&
inimi-e ris& to personnel
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Tran!former Connecton!
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19/12119 > Transformer Protection
5
* c
b
aa2a1
b1 b25152
2 1
*2 *1 c1 c2
5*
*2
*1 2
1
5251
a
b
cc2
c1
a2
a1
b1 b2
6*loc& face7 numbers refer to
position of lo% voltage phase (
neutral vector %ith respect to high
voltage phase ( neutral vector.
8ine connections made to highest
numbered %inding terminal available.
8ine phase designation is same as
%inding.
Tran!former Connecton!
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$hase displacement9
:roup 1
$hase displacement1;9
:roup 2
8ag phase displacement39
:roup 3
8ead phase displacement39
:roup 4
d9
=d9
d>->
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6*loc& #ace7 numbers refer to position of lo% voltage
phase(neutral vector %ith respect to high voltage phase
neutral vector
8ine connections made to highest numbered %inding
terminal available
8ine phase designation is same as %inding
E#amp$e % & D' %% Tran!former
B1B2 b2b1
a2a1A1A2
C1C2 c2c1
?uestion @ o% to connect %indings A
HighVoltage
Windings
LowVoltage
Windings
A PhaseWinding
s
B PhaseWindings
C PhaseWinding
s
Tran!former Connecton!
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O(erc"rrent Protecton
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23 > Transformer Protection
)e/uirements
#ast operation for primar! short circuits
iscrimination %ith do%nstream protections
Operation %ithin transformer %ithstand
+on(operation for short or long term overloads
+on(operation for magnetising inrush
Tran!former O(erc"rrent Protecton
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24 > Transformer Protection
B0
80
9
1
9 set to 1.2 ( 1.3 x through fault level
U!e of In!tantaneo"! O(erc"rrent Protecton
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25 > Transformer Protection
*oncerns rela! response to offset %aveforms C*
transientD
efinition
I( ) I*
I* x (++
I1 "tead! state
rms pic& up
current
I2 #ull! offset
rms
pic&up
current
I(
I*
!C
Tran!ent O(erreac)
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26 > Transformer Protection
HV2
51
51
51
LVHV1
Time LV
HV1HV2
CurrentI!LV"
1#2I!LV"
I!HV"
In!tantaneo"! H*) Set O(erc"rrent Re$a' App$e+ to a Tran!former
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27 > Transformer Protection
I,- I,-
I,-
I,-
+.//
C"rrent D!tr,"ton
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28 > Transformer Protection
I,-9.;>> I,-
9.4 sec
80 rela!
0 rela!
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32 > Transformer Protection
P $$ $ T f
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33 > Transformer Protection
:rid suppl!
#eeders
1
1
>F
>F
1
1
Para$$e$ Tran!former!Drectona$ Re$a'! -%.
P $$ $ T f
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34 > Transformer Protection
11
1
1
5us"ection
Para$$e$ Tran!former!Drectona$ Re$a'! -/.
:rid suppl!
#eeders
1
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36 > Transformer Protection
Eart) Fa"$t Protecton
Tran!former Eart) Fa"$t!
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37 > Transformer Protection
1 p.u. turns3 p.u. turns
x'$
$)
) '#$rotective)ela!
:3 ratioturnsEffective
. 3
. currentFault : atfaultaFor
. x3
current,primaryThus, valuesloadfulltocurrentE/FlimitsResistor
F.L.2
F.L.
F.L.
χ
χ χ χ
χ χ
=
Ι=Ι=
Ι=Ι
secondary!.T.thenr,transformeof currentload
fullon"asedisside#primary$onratio!.T.%f
3
circuit2
χ =
Tran!former Eart) Fa"$t!
O(erc"rrent Re$a' Sen!t(t'
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38 > Transformer Protection
χI
&'
(vercurrent
Relay
I$ as multi%le
o$ I#L#
1#&
'
(
)
*
+
,
-tar-ide
.elta-ide
, + * ) ( ' 1#&χ
%#u##/0ercurrent ela -etting 3
I#L#
O(erc"rrent Re$a' Sen!t(t' to Eart) Fa"$t! -%.
O(erc"rrent Re$a' Sen!t(t'
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39 > Transformer Protection
1&
'
(
)
*
5
+
,
2
1
, + * ) ( ' 1#&χ
%#u##
I$ as multi%le
o$ I#L#
-tar-ide
.elta-ide
O(erc"rrent Re$a' Sen!t(t' to Eart) Fa"$t! -/.
χI
&'
(vercurrent
Relay
O(erc"rrent Re$a' Sen!t(t'
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40 > Transformer Protection
χ
I
IP I4
1&
'
(
) *
5
+
,
2 1
, + * ) ( ' 1#&
χ
%#u##
I4
IP
I
O(erc"rrent Re$a' Sen!t(t' to Eart) Fa"$t! -0.
I$ as multi%le
o$ I#L#
Eart) Fa"$t on Tran!former Wn+n*
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41 > Transformer Protection
ifferential )ela! "etting G of "tar Winding $rotected19G ;G
29G 41G
39G 2;G
49G 1FG
9G FG
Eart) Fa"$t on Tran!former Wn+n*
I
ifferential)ela!
"etting I"
χ
#or rela! operation, I H I"
e.g. 'f I" 29G, then H 29G for
operation
i.e. χ H IG
Thus IG of %inding is not protected
χ
2
√ 3I
χ2
√ 3
Unre!trcte+ Eart)fa"$t Protecton -%.
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42 > Transformer Protection
$rovides bac&(up protection for s!stem
Time dela! re/uired for co(ordination
Unre!trcte+ Eart)fa"$t Protecton -%.
51
51
51
514
Unre!trcte+ Eart) fa"$t Protecton
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43 > Transformer Protection
*an provide better sensitivit!
C*.T. ratio not related to full load currentD
C'mproved 6effective7 settingD
$rovides bac& up protection for transformer and s!stem
51
51
51
51451
4
Unre!trcte+ Eart) fa"$t Protecton
Star Wn+n* REF
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44 > Transformer Protection
$rotected
=one
)E
#
)ela! onl! operates for earth faults %ithin protected -one.
Jses high impedance principle.
"tabilit! level @ usuall! maximum through fault level of
transformer
Star Wn+n* REF
Re!trcte+ E1F Protecton
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45 > Transformer Protection
80 restricted E#
protection trips
both 0 and 80 brea&er
)ecommended setting @ 19G
rated
Re!trcte+ E1F Protecton
5 * +
Re!trcte+ E1F Protecton
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46 > Transformer Protection
5 * +
80 restricted E# protection trips both 0 and 80 brea&er
)ecommended setting @ 19G rated
Re!trcte+ E1F Protecton
De$ta Wn+n* Re!trcte+ Eart) Fa"$t
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47 > Transformer Protection
$rotected -one
)E#
"ource
elta %inding cannot suppl! -ero se/uence current tos!stem
"tabilit! @ *onsider max 80 fault level
)ecommended setting @ less than 39G minimum earth fault
level
De$ta Wn+n* Re!trcte+ Eart) Fa"$t
H*) Impe+ance Prncp$e
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48 > Transformer Protection
ProtectedCircuit
6
7
CT
L
6
7
CT
LI
I-
-
T
V-
L L
H*) Impe+ance Prncp$e
0oltage cross )ela! *ircuit 0" I# C)*T K 2)8D
"tabilising resistor )"T limits spill current to I" Crela! settingD
∴ )"T ( )) %here )) rela! burden
*T &nee point
0L$
20"
2I#
C)*T
K 2)8
D
0"
I"
T)e U!e Of Non2Lnear Re!!tor! -3etro!$!.
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49 > Transformer Protection
uring internal faults the high impedance rela! circuit
constitutes an excessive burden to the *TMs.
ver! high voltage develops across the rela! circuit and
the *TMs.
*auses damage to insulation of *T, secondar!%inding and rela!.
agnitude of pea& voltage 0$ is given b! an approximate
formula Cbased on experimental resultsD
0$ 2 √ 20L C0# ( 0LD
Where 0# "%gr. #ault )ating in amps x = of rela!
circuit *T ratio
N setting
etrosil re/uired if 0$ H 3&0
T)e U!e Of Non Lnear Re!!tor! -3etro!$!.
Non2Lnear Re!!tor! -3etro!$!.
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50 > Transformer Protection
I/P
-T
V-V7
etrosil *haracteristic
0 * ' β
"uitable values of * β
chosen based on @
ax secondar! current under fault conditions
)ela! setting voltage
Non Lnear Re!!tor! -3etro!$!.
REF Protecton E#amp$e
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51 > Transformer Protection
17VA!58"11&&&V+15V
1*&&91CT
+#'Ω
(&7VA
-1*&&91
CT
+#(Ω
7CA:1+
I-
Am%2 Core )9*)mm!)#+1Ω9;m"1&&m Long
*alculate @
1D "etting voltage C0"D
2D 0alue of stabilising
resistor re/uired
3D Effective setting
4D $ea& voltage
developed b! *TMs
for internal fault
REF Protecton E#amp$e
So$"ton -%.
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52 > Transformer Protection
Earth fault calculation @(
Jsing ;90 base
"ource impedance 1 p.u.
Transformer impedance 9.9 x ;9 4 p.u.
1
Total impedance 14
p.u.
∴
'1 1 9.9F14 p.u. 14
5ase current ;9 x 19>
√ 3 x 41
1112I> mps
∴ '# 3 x 9.9F14 x 1112I>
23;49 mps Cprimar!D
14.I mps Csecondar!D
1 $.J.1 4
I1
4
I2
4
I9
"e/uence iagram
So$"ton -%.
So$"ton -/.
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53 > Transformer Protection
C1D "etting voltage0" I# C)*T K 2)8D
ssuming 6earth7 *T saturates,
)*T 4.; ohms
2)8 2 x 199 x F.41 x 19(3 1.4;2 ohms
∴ "etting voltage 14.I C4.; K 1.4;2D
I3.> 0olts
C2D "tabilising )esistor C)"D
)" 0" ( 1
I" I"2 Where '" rela! current setting
∴ )" I3.> ( 1 ;3> ohms
9.1 9.12
So$"ton -/.
So$"ton
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54 > Transformer Protection
C4D $ea& voltage 2√20L C0# ( 0LD
0# 14.I x 0" 14.I x I3> 13I4> 0olts
I"
#or PEarthM *T, 0L 1.4 x 23> 339 0olts Cfrom graphD
∴ 0$EL 2√2 x 339 x C13I4> ( 339D
>&0Thus, etrosil voltage limiter %ill be re/uired.
So$"ton
Tra+tona$ Lar*e Tran!former
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55 > Transformer Protection
Tra+tona$ Lar*e Tran!former Protecton Pac4a*e
33L
0
9
1
299
1903311L0 1+ ;F
>99
>4
>99
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Dfferenta$ Protecton
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57 > Transformer Protection
Overall differential protection ma! be ustified for
larger transformers Cgenerall! H 0D. $rovides fast operation on an! %inding
easuring principle @
5ased on the same circulating current principle as the
restricted earth fault protection
o%ever, it emplo!s the biasing techni/ue, to maintain
stabilit! for heav! through fault current
5iasing allo%s mismatch bet%een *T outputs.
't is essential for transformers %ith tap changing
facilit!.
nother important re/uirement of transformer
differential protection is immunit! to magnetising in
rush current.
5a!e+ Dfferenta$ Sc)eme
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58 > Transformer Protection
5'"5'" I*I(
O$E)TE
I( )
I*
ifferential
*urrent
O$E)TE
)E"T)'+
ean Through*urrent
I( 0
I*
*
I( )
I*
Dfferenta$ Protecton
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59 > Transformer Protection
80
)
0
$)OTE*TE
=O+E
*orrect application of differential protection re/uires *T ratio
and %inding connections to match those of transformer.
*T secondar! circuit should be a 6replica7 of primar! s!stem.
*onsider @
C1D ifference in current magnitude
C2D $hase shift
C3D =ero se/uence currents
Dfferenta$ Connecton! An+ po$art' mar4n*!
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60 > Transformer Protection
$1 $2 2 1 a1 a2 $2 $1
5 *
p ' *
U!e of Interpo!n* CT
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61 > Transformer Protection
))
)
$1 $2 2 1 a1 a2 $2 $1
"2 "1 $1 $2
'nterposing *T provides @ 0ector correction
)atio correction
=ero se/uence compensation
"1 "2 "2 "1
p *
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62 > Transformer Protection
Interpo!n* c"rrent tran!former!
Interpo!n* c"rrent tran!former!
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63 > Transformer Protection
Interpo!n* c"rrent tran!former!
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64 > Transformer Protection
Interpo!n* c"rrent tran!former!
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Dfferenta$ Protecton
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81 > Transformer Protection
"2"1
$1$212 a2a1$2
10
>>&0 11&019 ;99
$1
!1
"1"2
:iven above@ +eed to consider (
C1D Winding full load current C2D Effect of tap changer Cif an!D
C3D *.T. polarities
ssuming no tap changer
#ull load currents@( >>&0@ 131 mp 4.3F mps secondar!
11&0@ F;F mp 4.I2 mps secondar!
o%ever, re/uire 11&0 *.T.Ms to be connected in
Thus, secondar! current √3 x 4.I2 ;.2
∴ 1ATI2 C211ECTI23 IS 1E4UI1E!
Dfferenta$ Protecton
19 ;99
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82 > Transformer Protection
))
)
$1 $2 2 1 a1 a2 $2 $1
"1 "2 $1 $2
4.I2
"1 "2 "2 "1
4.3F
C2.>D CD
19 ;99
't is usual to connect 11&0 *.T.Ms in and utilise a interposing *.T. Cthis
method reduces lead 0 burden on the line *.T.MsD
*urrent from >>&0 side 4.3F mpThus, current re/uired from %inding of int. *.T. 4.3F mp
*urrent input to %inding of int. *.T. 4.I2 mp
∴)e/uired int *.T. ratio 4.I2 4.3F 4.I2 2.2
√3
a! also be expressed as @ 2.>
Effect of Tap C)an*er
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83 > Transformer Protection
e.g. ssume >>&0 KG, (1G
'nterposing *.T. ratio should be based on mid tap position
id Tap C(GD >2.F &0
$rimar! current C1 0D 13; mp
"econdar! current 4.> mp
∴ 'nterposing *.T. ratio re/uired 4.I2 4.>
√3
C D
4.I2 2.>>
a! also be expressed as @ 2.F
*ompared %ith 2.> based on nominal voltage
Com,ne+ Dfferenta$ an+ Re!trcte+ Eart) Fa"$t Protecton
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84 > Transformer Protection
To differential rela!
"2
"1
$1
$2)E#
"2
"1$1
$2
"2"1$1 $2
a2a112
Re!trcte+ Eart) Fa"$t Protecton
T)ree Wn+n* Tran!former
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85 > Transformer Protection
20
11L0
>30
132L0
1>99399
90
33L0
1999
4.I
2.;;
19.33
2.;;
.1
All interposing CT ratio5s referto common 67A $ase 8/,67A9
Tra+tona$ U!e of Interpo!n* CT
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86 > Transformer Protection
!1C(39QD
))
)
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87 > Transformer Protection
)ifferentialelement
*umeric Relay
+irtual interposin !T
+ectorialcorrection
Ratio
correction
+irtual interposin !T
Compen!aton
o-er transformer
Tran!former 3a*net!n* C)aracter!tc
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88 > Transformer Protection
T%ice+ormal
#lux
+ormal
#lux
+ormal+o 8oad*urrent
+o 8oad *urrentat T%ice +ormal
#lux
C)aracter!tc
3a*net!n* Inr"!) C"rrent Stea+' State
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89 > Transformer Protection
m
m
0
)
Φ
7
mI
Stea+' State
3a*net!n* Inr"!) C"rrent S6tc) on at Vo$ta*e 7ero 2 No re!+"a$ f$"#
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90 > Transformer Protection
m
Φ
Φm*
7
I
S6tc) on at Vo$ta*e 7ero No re!+"a$ f$"#
Tran!former Dfferenta$ ProtectonEffect of 3a*net!n* C"rrent
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91 > Transformer Protection
Effect of 3a*net!n* C"rrent
ppears on one side of transformer onl!
"een as fault b! differential rela!
+ormal stead! state magnetising current is less thanrela! setting
Transient magnetising inrush could cause rela! to
operate
Tran!former Dfferenta$ ProtectonEffect of 3a*net!n* Inr"!)
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92 > Transformer Protection
Effect of 3a*net!n* Inr"!)
"O8JT'O+ 1 @ T'E E8<
llo%s magnetising current to die a%a! before rela! canoperate
"lo% operation for genuine transformer faults
Tran!former Dfferenta$ ProtectonEffect of 3a*net!n* Inr"!)
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93 > Transformer Protection
Effect of 3a*net!n* Inr"!)
"O8JT'O+ 2 @ 2+ Cand TD )O+'* )E"T)'+T
a&es rela! immune to magnetising inrush
"lo%er operation ma! result for genuine transformer faults
if *T saturation occurs
T'pca$ 3a*net!n* Inr"!)Wa(eform!
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94 > Transformer Protection
A
C
:
Wa(eform!
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95 > Transformer Protection
Inter2T"rn Fa"$t Protecton
Inter2T"rn Fa"$t
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96 > Transformer Protection
+ominal turns ratio
#ault turns ratio
*urrent ratio
( 11,999 249
( 11,999 1
( 1 11,999
)e/uires 5uchhol- rela!
*T
E
"horted
turn
8oad
Intert"rn Fa"$t C"rrent 1 N"m,er of T"rn! S)ort Crc"te+
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97 > Transformer Protection
199
;9
>9
49
29
9 19 1 29 2
19
;
>
4
2
#ault current in short
circuited turns
$rimar! input current
#ault current
Cmultiples of rated currentD
$rimar! current
Cmultiples of rated currentD
Turn short(circuited Cpercentage of %indingD
of T"rn! S)ort Crc"te+
Non2e$ectrca$ Protecton
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98 > Transformer Protection
5uchhol- $rotection
$ressure )elief $rotection
"udden $ressure $rotection
Winding Temperature $rotection
Oil Temperature $rotection
Oil 8evel bnormal $rotection
5"c))o$8 Protecton
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99 > Transformer Protection
The function of the rela! is to detect an abnormal condition
%ithin the tan& and send an alarm or trip signal.
5"c))o$8 operate 6)en&
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100 > Transformer Protection
:as produced from the transformer due to fault
n oil surge from the tan& to the conservator
complete loss of oil from the conservator Cver! lo% oil levelD
Pre!!"re Re$ef De(ce
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101 > Transformer Protection
TransformersM last line of defense against internal pressure
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O$ Temperat"re Protecton
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103 > Transformer Protection
T!picall! sealed spiral(bourdon(tube dial indicators %ith li/uid(
filled bulb sensor
5"c))o$8 Re$a' In!ta$$aton
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104 > Transformer Protection
x internal pipe
diameter CminimumD
3 x internal pipe
diameter CminimumD
Transformer
3 minimum
Oil conservator
*onservator
5"c))o$8 Re$a'
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105 > Transformer Protection
$etcoc&
*ounter balance%eight
Oil level
#rom transformer
perture aduster
eflector platerain plug
Trip buc&et
To oilconservator
ercur! s%itch
larm buc&et
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106 > Transformer Protection
O(erf$"#n* Protecton
Tran!former protecton
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107 > Transformer Protection
Over fluxing protection
Over fluxing arises principall! from the
follo%ing s!stem conditions.
igh s!stem voltage
8o% s!stem fre/uenc!
:eomagnetic disturbances
The latter result in lo% fre/uenc! earthcurrents circulating through a transmission
s!stem.
O(erf$"#n*
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108 > Transformer Protection
:enerator transformers
:rid transformers
Jsuall! onl! a problem during run(up or shut do%n, but can be
caused b! loss of load load shedding etc.
#luxΦ ∝ 0
f
Effects of overfluxing @ 'ncrease in magnetising current
'ncrease in %inding temperature
'ncrease in noise and vibration
Overheating of laminations and metal parts Ccaused b! stra! fluxD
$rotective rela! responds to 0f ratio "tage 1 ( lo%er .0.).
"tage 2 ( Trip field
O(erf$"#n* 5a!c T)eor'
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109 > Transformer Protection
m2
'e
m
0 &fΦ
*J"E"
8o% fre/uenc!
igh voltage
:eomagnetic disturbances
E##E*T"Tripping of differential element CTransient overfluxingD
amage to transformers C$rolonged overfluxingD
V1H8 O(erf$"#n* Protecton
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110 > Transformer Protection
Φ
0 f α
L
Trip and alarm outputs for clearing prolonged overfluxing
larm @ efinite time characteristic to initiate corrective action
Trip @ 'T or T characteristic to clear overfluxing condition
"ettings
$ic&(up 1. to 3.9 i.e. 1190 x 1.9 2.31
9-
T setting range 9.1 to >9 seconds
V1H8 C)aracter!tc!
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111 > Transformer Protection
1999
199
19
11 1.1 1.2 1.3 1.4 1. 1.>
Operating
time CsD
0 -
"etting
L >3L 49
L 29
L
L 1
t 9.; K 9.1; x L
C ( 1D2
Enables co(ordination %ith plant %ithstand characteristics
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112 > Transformer Protection
T)erma$ O(er$oa+ Protecton
O(er temperat"re
: ll d d l d t ti l d l
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113 > Transformer Protection
:enerall! regarded as overload protection also deals
%ith failure of or interference %ith pumps and fans or
shutting of valves to pumps
Winding hot spot temperature is the main issue, but both
oil and %inding temperature are usuall! measured and
used to@
R initiate an alarm
R trip circuit brea&ers
R control fans and pumps
O(er temperat"re
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114 > Transformer Protection
T%o temperatures must be monitored@
SWinding temperature CPWT'MD (Cshort
thermal D this can rise rapidl!, %ithout
much of an increase in oil temperature
SOil temperature CPOT'MD (Clong thermal D
this can rise slo%l! to a critical point
%ithout an unacceptable %inding
temperature increase
T'pca$ a$arm an+ trp $e(e$!
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115 > Transformer Protection
%inding alarm ( I9U* to
119U*
V %inding trip ( 119U* to
13U*
V oil alarm ( ;9U* to IU*
V oil trip ( IU* to 11U*
O(er)eatn* Protecton
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116 > Transformer Protection
' load
Tsetting
' loadTop oil of po%er transformer
eater
Thermalreplica
Temperaturesensing resistor
)emote
Temp. indication8ocal
Off
On
Off
On
larm
Trip
$umpcontrol
#ancontrol
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117 > Transformer Protection
T'pca$ Tran!former Protecton to
Fee+er!
Protecton of Para$$e$Tran!former Fee+er!
iher
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118 > Transformer Protection
iher voltae"us"ar
(!0 (! 0
FT1 FT1
REF
)
h
REF
)
hT T
REF REF
2 ' 2'1EF2 stae 1EF2 stae
)(! (! (! )(!
LoadLoad
Lo-er voltae
"us"ar
Tran!former Fee+er!
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119 > Transformer Protection
#EEE
)
$'8OT
"$W$
W
#or use %here no brea&er separates the transformer from thefeeder.
Transformer inrush current must be considered.
'nrush is a transient condition %hich ma! occur at the instant of
transformer energisation.
ag. 'nrush current is not a fault condition
∴ $rotection must remain stable.
*T provides a bloc&ing signal in the presence of inrush
current and allo%s protection to be used on transformer feeders.
Tran!former Fee+er Protecton
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120 > Transformer Protection
)y''
2'
II
III
I
1' 12
0TW
924F5!
'6
%L(T1 4!%4!%
4!T4!T23
26
!
5
ii
iii
i'2
12 1'
!
5
2&
27
28
29
23
26
2&
27
28
29
27
29
'9
'
;
3
'
'7
'7
'7
'
'9
'
'3'6
'7
'
23
26
2&
27
28
29
23
262&
27
28
29
'9
'7
1'
Protectonof Tran!former Fee+er!
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o-er transformer
&6<
1cheme
+irtual interposin !T
+ectorialcorrection
Ratiocorrection
+irtual interposin !T