Muhsin Transformer protection 2015.ppt

8/20/2019 Muhsin Transformer protection 2015.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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7/1147 > Transformer Protection


Introduction

Transformers are a critical and expensivecomponent of the power system !ue tolong lead time for repair and replacementof transformers" a ma#or goal oftransformer protection is limiting thedamage to a faulted transformer The

comprehensive transformer protectionprovided $y multiple function protectiverelays is appropriate for criticaltransformers of all applications




The type of protection for thetransformers varies depending on theapplication and importance of the

transformer Transformers are protectedprimarily against faults and overloads Thetype of protection used should minimi%ethe time of disconnection for faults withinthe transformer and to reduce the ris of

catastrophic failure to simplify eventualrepair



TRANSFORMER

PROTECTION

Any extended operation of thetransformer under a$normalcondition such as faults or

overloads compromises the lifespan of the transformer" whichmeans ade'uate protection should$e provided for 'uicer isolation ofthe transformer under suchcondition



Types of Transformer Failures

( )inding failures due to short circuits*turn+turn faults" phase+phase faults"phase+ground" open winding,

-Core faults *core insulation failure"

shorted laminations,.Terminal failures *open leads" loose

connections" short circuits,

/0n+load tap changer failures*mechanical" electrical" short circuit"

overheating,

1A$normal operating conditions *over

2uxing" overloading" overvoltage,



CAUSES OF FAILURES

Lightning Surges

Line Surges/ External Short Circuits

Over-loading

Deterioration Of insulation

Moisture Ingress

Poor maintenance

Poor Wormanshi!/Manufacturing



Failure Statistics

Lightning Surges- "#$

Line Surges/ Short Circuits- %&$

Over Loading- '$

Moisture Ingress- ($

Deterioration Of Insulation- ")$

Poor Wormanshi!/ Manufacturing- $

Inade*uate Maintenance- "%$

Loose Connection- +$

Others- %&$



Line Surges

Line Surge ,or Line Disturance. is the numer one

cause for all t!es of transformers failures0

1his categor includes s2itching surges3 voltage s!ies3

line faults/flashovers3 and other transmission anddistriution ,14D. anormalities0

1his significant !ortion of transformer losses indicates

that more attention should e given to !roviding surge

!rotection3 or testing the ade*uac of existing surge

!rotection0



Deterioration of Insulation

Insulation Deterioration is found to e the second

leading cause of failure0 1he average age of the

transformers that fails due to insulation deterioration is

around %& ears against a general life ex!ectanc of #&

to #) ears0



Factors Affecting LifeExpectancy Of Insulation

Misa!!lication

5iration

6igh O!erating 1em!erature

Overloading

Care of Control E*ui!ment

Lac of Cleanliness

Care of Idle or S!are E*ui!ment

Careless or 7egligent O!eration



Inadeuate !aintenance

Inade*uate Maintenance 2as the third leading cause of

transformer failures0

1his categor includes disconnected or im!ro!erl set

controls3 loss of coolant3 accumulation of dirt and oil3and corrosion0

Inade*uate maintenance has to ear the lame for not

discovering inci!ient troules 2hen there 2as am!le

time to correct it



"oor#$or%mans&ip'!anufacture

8 lo2 !ercent of the total failures are attriuted to Poor

Wormanshi! or Manufacturer9s Defects these das0

Loose or unsu!!orted leads3 loose locing3 !oor

ra:ing3 inade*uate core insulation3 inferior short circuitstrength3 and foreign o;ects left in the tan are the

reasons falling under the aove categor0



O(erloading

It includes onl those transformers that

ex!erienced a sustained load that exceeded the

name!late ca!acit0

Often3 the overloading occurs 2hen the !lant or theutilit slo2l increases the load in small increments

over time0 1he ca!acit of the transformer is

eventuall exceeded3 resulting in excessive

tem!eratures that !rematurel ages the insulation0

8s the transformer9s !a!er insulation ages3 the

strength of the !a!er is reduced0

1hen3 forces from an outside fault ma cause a

deterioration of the insulation3 leading to failure0



!oisture

1he Moisture categor includes failures caused

floods3 lea !i!es3 leaing roofs3 2ater entering the

tans through leaing ushings or fittings3 and

confirmed !resence of moisture in the insulating oil0



Loose Connections

Loose Connections could e included in the

Maintenance categor0

1his categor includes 2ormanshi! and maintenance

in maing electrical connections0One !rolem is the im!ro!er mating of dissimilar metals3

although this has decreased some2hat in recent ears0

8nother !rolem is im!ro!er tor*uing of olted

connections0



Protection Of

1ransformer



Auxiliary Faults

- Mainly related to the Tank, Oil, etc

- Detection by Pressure Switches /

Temp Switches

- !inked with the trip circuit lo"ic


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Trans#ormer

Proection Philosophy

$ Main Protection %&nternal Faults'

( )ack up Protection % *xternal #aults'

+ !ocation

Si-e


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!&ST OF P.OT*T&O0S

Main Protections

Di##erential

.estricted */F

)ack up Protections

O/ 1 */F % Primary Side'

O/ 1 */F % Secondary Side'

urrent 2nbalance

Thermal O3erload

O3er Fluxin"

O3er 4olta"e/2nder 4olta"e

O3er Fre5uency / 2nder Fre5uency

Directional O/ 1 Directional */F

Power %Forward / .e3erse'

6ero Se5uence 4olta"e

4olta"e 2nbalance

)reaker Failure

Auxiliary Protections

Oil Temperature

7as pressure

Oil !e3el

4ibration

oolin" Fans trip


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Trans#ormer

89 8$ 890 8$0

89 8$ 890 8$0

(: 8;

*xternal Faults

89/8$ &DMT O3er urrent

890/8$0 &DMT *arth Fault

(: 2nder 4olta"e

8; O3er 4olta"e

!ess than $ M4A


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T.A0SFO.M*. P.OT*T&O0

Trans#ormer

89 8$ 890 8$0

89 8$ 890 8$0

(: 8;

*xternal Faults

89/8$ &DMT O3er urrent

890/8$0 &DMT *arth Fault

(: 2nder 4olta"e

8; O3er 4olta"e

; Thermal O3er !oad

= urrent 2nbalance

( O3er Fluxin"

More than $9 M4A; =

(


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Transformer Connections

T f C ti


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8

<

C c

aa%a"

" % numers refer to

!osition of lo2 voltage !hase -

neutral vector 2ith res!ect to high

voltage !hase - neutral vector0

Line connections made to highestnumered 2inding terminal availale0

Line !hase designation is same as

2inding0


T f ) t *


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Phase dis!lacement&

?rou! "

Phase dis!lacement"@&

?rou! %

Lag !hase dis!lacement#&

?rou! #

Lead !hase dis!lacement#&

?rou! '

A&

Dd&

Bd&

A+

Dd+D:+

Ad"

D"

A:"

Ad""

D""

A:""

Transformer )ector *roups

T f C ti


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=Cloc ace> numers refer to !osition of lo2 voltage

!hase-neutral vector 2ith res!ect to high voltage !hase

neutral vector

Line connections made to highest numered 2inding

terminal availale

Line !hase designation is same as 2inding

Example + , Dy ++ Transformer

B1B2 b2b1

a2a1A1A2

C1C2 c2c1

uestion 6o2 to connect 2indings F

HighVoltage

Windings

LowVoltage

Windings

A PhaseWinding

s

B PhaseWindings

C PhaseWinding

s



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O(ercurrent "rotection

T f O t " t ti


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Ge*uirements

ast o!eration for !rimar short circuits

Discrimination 2ith do2nstream !rotections

O!eration 2ithin transformer 2ithstand

7on-o!eration for short or long term overloads

7on-o!eration for magnetising inrush

Transformer O(ercurrent "rotection

U f I t t O t " t ti


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H65

L5

)&

)"

)& set to "0% - "0# x through fault level

Use of Instantaneous O(ercurrent "rotection

Transient O erreac&


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Concerns rela res!onse to offset 2aveforms ,DC

transient.

Definition

&( + &-

&- x (44

&" Stead state

rms !ic u!

current

&% ull offset

rms

!icu!

current

&(

&-

!C

Transient O(erreac&

Instantaneous -ig& Set O(ercurrent


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HV2

51

51

51

LVHV1

Time LV

HV1HV2

CurrentI!LV"

1#2I!LV"

I!HV"

Instantaneous -ig& Set O(ercurrent Relay Applied to a Transformer

C t Di t i. ti


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&.5 &.5

&.5

&.5

4633

Current Distri.ution


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&.5&0@++ &.5

&0' sec

L5 rela

65 rela

"arallel Transformers


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?rid su!!l

eeders

)"

)"

+(

+(

)"

)"

"arallel TransformersDirectional Relays /+0

"arallel Transformers


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)")"

)"

)"


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Eart& Fault "rotection

Transformer Eart& Faults


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" !0u0 turns# !0u0 turns

xIP

PG

G IProtectiveGela

: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 =

Transformer Eart& Faults

O(ercurrent Relay Sensiti(ity


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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(ercurrent Relay Sensiti(ity to Eart& Faults /+0

O(ercurrent Relay Sensiti(ity


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1&

'

(

)

*

5

+

,

2

1

, + * ) ( ' 1#&χ

%#u##

I$ as multi%le

o$ I#L#

-tar-ide

.elta-ide

O(ercurrent Relay Sensiti(ity to Eart& Faults /10

χI

&'

(vercurrent

Relay

Unrestricted Eart&fault "rotection /+0


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Provides ac-u! !rotection for sstem

1ime dela re*uired for co-ordination

Unrestricted Eart&fault "rotection /+0

51

51

51

514

Unrestricted Eart& fault "rotection


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Can !rovide etter sensitivit

,C010 ratio not related to full load current.

,Im!roved =effective> setting.

Provides ac u! !rotection for transformer and sstem

51

51

51

51451

4

Unrestricted Eart& fault "rotection

Star $inding REF


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Protected

Bone

GE

Gela onl o!erates for earth faults 2ithin !rotected :one0

Jses high im!edance !rinci!le0

Stailit level usuall maximum through fault level of

transformer

Star $inding REF

Restricted E'F "rotection


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L5 restricted E/

!rotection tri!s

oth 65 and L5 reaer

Gecommended setting "&$

rated


8 < C 7



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8 < C 7

L5 restricted E/ !rotection tri!s oth 65 and L5 reaer

Gecommended setting "&$ rated


Delta $inding Restricted Eart& Fault


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Protected :one

GE

Source

Delta 2inding cannot su!!l :ero se*uence current tosstem

Stailit Consider max L5 fault level

Gecommended setting less than #&$ minimum earth fault

level

Delta $inding Restricted Eart& Fault

-ig& Impedance "rinciple


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ProtectedCircuit

6

CT

L

6

CT

LI

I-

-

T

V-

L L

-ig& Impedance "rinciple

5oltage 8cross Gela Circuit 5S & ,GC1 K %GL.

Stailising resistor GS1 limits s!ill current to &S ,rela setting.

∴ GS1 - GG 2here GG rela urden

C1 nee !oint

5P

%5S

%&

,GC1

K %GL

.

5S

&S

T&e Use Of 2on#Linear Resistors /!etrosils0


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During internal faults the high im!edance rela circuit

constitutes an excessive urden to the C19s0

8 ver high voltage develo!s across the rela circuit and

the C19s0

Causes damage to insulation of C13 secondar2inding and rela0

Magnitude of !ea voltage 5P is given an a!!roximate

formula ,ased on ex!erimental results.

5P % √ %5 ,5 - 5.

Where 5 S2gr0 ault Gating in am!s x B of rela

circuit C1 ratio

setting

Metrosil re*uired if 5P N #5

T&e Use Of 2on Linear Resistors /!etrosils0

2on#Linear Resistors /!etrosils0


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I/P

-T

V-V6

Metrosil Characteristic

5 C I β

Suitale values of C 4β

chosen ased on

Max secondar current under fault conditions

Gela setting voltage

2on Linear Resistors /!etrosils0

REF "rotection Example


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16VA!57"

11&&&V+15V

1*&&81CT 9

+#'Ω

(&6VA

-1*&&81

CT 9

+#(Ω

6CA:1+

I- 9

Am%2 Core )8*)mm!)#+1Ω8;m"1&&m Long

Calculate

". Setting voltage ,5S.

%. 5alue of stailising

resistor re*uired

#. Effective setting

'. Pea voltage

develo!ed C19s

for internal fault

otect o a p e

Solution /+0


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Earth fault calculation -

Jsing @&M58 ase

Source im!edance " !0u0

1ransformer im!edance &0&) x @& ' !0u0

"

1otal im!edance "'

!0u0

∴

I" " &0&("' !0u0 "'


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,". Setting voltage5S & ,GC1 K %GL.

8ssuming =earth> C1 saturates3

GC1 '0@ ohms

%GL % x "&& x (0'" x "&-# "0'@% ohms

∴ Setting voltage "'0 ,'0@ K "0'@%.

#0+ 5olts

,%. Stailising Gesistor ,GS.

GS 5S - "

&S &S% Where IS rela current setting

∴ GS #0+ - " @#+ ohms

&0" &0"%

/ 0

Solution


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,'. Pea voltage %√%5 ,5 - 5.

5 "'0 x 5S "'0 x #+ "#'+ 5olts

&S

or Earth9 C13 5 "0' x %#+ ##& 5olts ,from gra!h.

∴ 5PE8 %√% x ##& x ,"#'+ - ##&.

+51hus3 Metrosil voltage limiter 2ill e re*uired0


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Differential "rotection

Fundamental of differential protection


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p

Types of differential -ig& impedance differential,,

-ere a &ig& impedance is added to relay circuit to pre(ent relay

operation due to CT saturation under t&roug& fault conditions3

T&is is (ery sensiti(e and fast operating for internal faults3

4iased differential ,

-ere t&e operation depends upon differential current exceeding

t&e .ias current3

T&e .ias c&aracteristics is (aria.le so t&at it is applica.le to a

5ide (ariation in transformer design and configuration3 T&is

.ias slope is set to sta.ili6e t&e protection for small differential

currents7 5&ic& flo5 due to tap c&anger (ariation and CT

tolerance under t&roug& fault conditions3


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-armonic Restraint


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.*ST.A&0TS &0 D&FF*.*0T&A! .*!A>S

(0D ?A.MO0& .*ST.A&0T

@?*0 A T.A0SFO.M*. &S S@&T?*D O0,

T?* D&FF*.*0T&A! .*!A> MA> S*0S* A

D&FF*.*0T&A! 2..*0T A0D &0&T&AT* T.&P

T?&S &S D2* TO T?* MA70*T&S&07 2..*0T

&0.2S? O0 O0* S&D* OF T?* T.A0SFO.M*.

T?&S @&!! .*S2!T &0 A !A.7* 4A!2* OF

&$&( FO. A)O2T O. 8 >!*S


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.*ST.A&0TS &0 D&FF*.*0T&A! .*!A>S

8T? ?A.MO0& .*ST.A&0T

@?*0 O4*. F!2B&07 O2.S &0 A T.A0SFO.M*.

T?* D&FF*.*0T&A! .*!A> MA> S*0S* A

D&FF*.*0T&A! 2..*0T A0D &0&T&AT* T.&P

T?&S &S D2* TO T?* ?&7? !*4*! OF F!2B

P.*S*0T &0 T?* O.* A2S&07 A0 A.T&F&&A!

&$&( FO. A S?O.T T&M*


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-armonics present in transformer c&arging in rus&current


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E(olution Of "rotecti(e Relaying3

Electromechanical single function

Static single function

Digital single function

Digital multifunction relas

7umerical multifunction relas

7umerical multifunction sstems

Functions of 2umerical Transformer


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"rotection


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Overall differential !rotection ma e ;ustified for

larger transformers ,generall N )M58.0 Provides fast o!eration on an 2inding

Measuring !rinci!le


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L5

G

65

PGO1EC1ED

BO7E

Correct a!!lication of differential !rotection re*uires C1 ratio

and 2inding connections to match those of transformer0

C1 secondar circuit should e a =re!lica> of !rimar sstem0

Consider

,". Difference in current magnitude

,%. Phase shift

,#. Bero se*uence currents

Differential Connections And polarity mar%ings


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P" P% 8% 8" a" a% P% P"

8 < C

Use of Interposing CT


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GG

G

P" P% 8% 8" a" a% P% P"

S% S" P" P%

Inter!osing C1 !rovides 5ector correction

Gatio correction

Bero se*uence com!ensation

S" S% S% S"


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Interposing current transformers



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S%S"

P"P%8"8% a%a"P%

")M58

++5 / ""5")&/) @&&/)

P"

D"

S"S%

?iven aove 7eed to consider -

,". Winding full load current ,%. Effect of ta! changer ,if an.

,#. C010 !olarities

8ssuming no ta! changer

ull load currents- ++5 "#" 8m! '0#( 8m!s secondar

""5 (@( 8m! '0% 8m!s secondar

6o2ever3 re*uire ""5 C0109s to e connected in

1hus3 secondar current √# x '0% @0)%8

∴ 8ATI0 C088ECTI09 IS 8E:UI8E!


")&/) @&&/)


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GG

G

P" P% 8% 8" a" a% P% P"

S" S% P" P%

'0%8

S" S% S% S"

'0#(8

,%0)+. ,).

")&/) @&&/)

It is usual to connect ""5 C0109s in and utilise a / inter!osing C010 ,this

method reduces lead 58 urden on the line C0109s.

Current from ++5 side '0#( 8m!1hus3 current re*uired from 2inding of int0 C010 '0#( 8m!

Current in!ut to 2inding of int0 C010 '0% 8m!

∴Ge*uired int C010 ratio '0% / '0#( '0% / %0)%

√#

Ma also e ex!ressed as ) / %0)+

Effect of Tap C&anger


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e0g0 8ssume ++5 K)$3 -")$

Inter!osing C010 ratio should e ased on mid ta! !osition

Mid 1a! ,-)$. +%0( 5

Primar current ,") M58. "#@ 8m!

Secondar current '0+ 8m!

∴ Inter!osing C010 ratio re*uired '0% / '0+

√#

, / .

'0% / %0++

Ma also e ex!ressed as ) / %0(

Com!ared 2ith ) / %0)+ ased on nominal voltage

Com.ined Differential and Restricted Eart& Fault "rotection


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1o differential rela

S%

S"

P"

P%GE

S%

S"P"

P%

S%S"

P" P%a%a"8"8%

Restricted Eart& Fault "rotection

T&ree $inding Transformer


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%)M5

8

""5

+#M5

8

"#%5 "+&&/)#&&/)

)&M5

8

##5

"&&&/)

'0)

%0@@

"&0##

%0@@

)0)"

)

)

All interposing CT ratio;s referto common


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D",-#&Q.

GG

G

Ad"",K#&Q.

Inter!osing C1 !rovides

5ector correction

Gatio correction

Bero se*uence com!ensation

2on#electrical "rotection


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1he function of the rela is to detect an anormal condition

2ithin the tan and send an alarm or tri! signal0

4uc&&ol6 operate 5&en,


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?as !roduced from the transformer due to

fault

8n oil surge from the tan to the conservator

8 com!lete loss of oil from the conservator

,ver lo2 oil level.

"ressure Relief De(ice


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1ransformers9 last line of defense against internal !ressure

Sudden "ressure "rotection


99/114


Jsed to detect sudden increase in gas !ressure caused

internal arcing

Set to o!erate efore !ressure relief device

Oil Temperature "rotection


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1!icall sealed s!iral-ourdon-tue dial indicators 2ith li*uid-

filled ul sensor

4uc&&ol6 Relay Installation


101/114


) x internal !i!e

diameter ,minimum.

# x internal !i!e

diameter ,minimum.

1ransformer

# minimum

Oil conservator

Conservator

4uc&&ol6 Relay


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Petcoc

Counter alance2eight

Oil level

rom transformer

8!erture ad;uster

Deflector !lateDrain !lug

1ri! ucet

1o oilconservator

Mercur s2itch

8larm ucet


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O(er fluxing "rotection

Transformer protection


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Over fluxing !rotection

Over fluxing arises !rinci!all from the

follo2ing sstem conditions0

6igh sstem voltage

Lo2 sstem fre*uenc

?eomagnetic disturances

1he latter result in lo2 fre*uenc earthcurrents circulating through a transmission

sstem0

O(er fluxing


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?enerator transformers

?rid transformers

Jsuall onl a !rolem during run-u! or shut do2n3 ut can e

caused loss of load / load shedding etc0

luxΦ ∝ 5

f

Effects of overfluxing Increase in magnetising current

Increase in 2inding tem!erature

Increase in noise and viration

Overheating of laminations and metal !arts ,caused stra flux.

Protective rela res!onds to 5/f ratio Stage " - lo2er 8050G0

Stage % - 1ri! field

O(er fluxing 4asic T&eory


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m%

Ie

m

5 fΦ

C8JSES

Lo2 fre*uenc

6igh voltage

?eomagnetic disturances

EEC1S1ri!!ing of differential element ,1ransient overfluxing.

Damage to transformers ,Prolonged overfluxing.

)'-6 O(erfluxing "rotection


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Φ

5 f α

1ri! and alarm out!uts for clearing !rolonged overfluxing

8larm Definite time characteristic to initiate corrective action

1ri! IDM1 or D1 characteristic to clear overfluxing condition

Settings

Pic-u! "0) to #0& i0e0 ""&5 x "0&) %0#"

)&6:

D1 setting range &0" to +& seconds

)'-6 C&aracteristics


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"&&&

"&&

"&

"" "0" "0% "0# "0' "0) "0+

M

O!erating

time ,s.

5 6:

Setting

+# '&

%&

)

"

t &0@ K &0"@ x

,M - ".%

Enales co-ordination 2ith !lant 2ithstand characteristics


109/114


T&ermal O(erload "rotection

O(er temperature

? ll d d l d t ti l d l


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?enerall regarded as overload !rotection also deals

2ith failure of or interference 2ith !um!s and fans or

shutting of valves to !um!s

Winding hot s!ot tem!erature is the main issue3 ut oth

oil and 2inding tem!erature are usuall measured and

used to

R initiate an alarm

R tri! circuit reaers

R control fans and !um!s

O(er temperature


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12o tem!eratures must e monitored

Winding tem!erature ,W1I9. -,short

thermal T. this can rise ra!idl3 2ithout

much of an increase in oil tem!erature

Oil tem!erature ,O1I9. -,long thermal T.

this can rise slo2l to a critical !oint

2ithout an unacce!tale 2inding

tem!erature increase

Typical alarm and trip le(els


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2inding alarm - &UC to

""&UC

V 2inding tri! - ""&UC to

"#)UC

V oil alarm - @&UC to )UC

V oil tri! - )UC to "")UC

O(er&eating "rotection


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I load

1Dsetting

I load1o! oil of !o2er transformer

6eater

1hermalre!lica

1em!eraturesensing resistor

Gemote

1em!0 indicationLocal

Off

On

Off

On

8larm

1ri!

Pum!control

ancontrol


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Muhsin Transformer protection 2015.ppt

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Transcript of Muhsin Transformer protection 2015.ppt