submission_ISTANBUL_2012.doc

8/12/2019 submission_ISTANBUL_2012.doc

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Experimental diagnostics measurement of Power Transformers in Industry

A. Aibeche 1*, S !rouni 1," and # A$roum 1

1 Laboratory of Applied Automation (LAA), FHC, University UMBB of Boumerdes, !""", AL#$%&A' epartments of *ysi+s, F , University UMBB of Boumerdes, !""", AL#$%&A

- Correspondin Aut*or/ $mail/ nababd'""10ya*oo.fr , said. rouni0ya*oo.+om and a roum0ya*oo.fr

Abstract%

2o analy3e t*e 4uality and dia nosti+ 5e used dissipation fa+tor for appli+ation to po5ertransformer ('!" M6A, 1!.7!8''" 6). 2*e insulation system is evaluated by multiplemeasurements of t*e insulation resistan+e 5indin and t*e diele+tri+ dissipation fa+tor and+apa+itan+e. 2*e use of dissipation fa+tor measurement at t*e end of t*e produ+tion +y+le notonly assures t*at t*e 4uality of t*e transformer meets t*e spe+ified levels but also provides insi *tinto t*e subtleties of t*e manufa+turin pro+ess. 2*is tool is used for many years for dia nosint*e *ealt* of ele+tri+al apparatus. 2*e test +ondu+ted in site to no5 t*e dryness of transformersinsulation. 2*is paper *i *li *ts e9perien+es on t*e measurements of t*e dissipation fa+tor usin# 2 and #uard mode te+*ni4ues of eart*lin systems ot*er t*an dryness of transformersinsulation.

&eywords% o5er 2ransformer, &nsulation %esistan+e, issipation Fa+tor, ia nosti+s.

1 Introduction:*ile operatin prin+iples of transformers remain t*esame, t*e +*allen es of maintainin and testintransformers *ave evolved alon 5it* transformerdesi n and +onstru+tion. Modern transformers are

desi ned to +loser toleran+es t*an transformers in t*e past. 2*us effe+tive re ular maintenan+e and testinis even more essential to +ontinued operation 5*entraditional ;over desi n< +annot be relied on toover+ome abnormal +onditions.2*e utility en ineer must be familiar 5it* all aspe+tsof maintenan+e and testin and ma e use of state oft*e art tools and te+*ni4ues for evaluatin transformer+ondition. :*ile on=line dia nosti+ systems and+omputeri3ed testin met*ods are very *elpful, t*eyare not a substitute for sound en ineerin >ud mentand e9pertise.

o5er 2ransformer is t*e si nifi+ant e4uipment in po5er transmission and distribution systems due to its*i * pri+e. ?ormally, t*e po5er transformer isdesi ned to *ave a lon operational life, 5*i+*depends on its operation and maintenan+e.$le+tri+al properties of insulation +*an e due to a e+onditions of operatin and +ontinuous stress. 2*emain +ontributor to t*e brea do5n of *i * volta ee4uipments is t*e insulation failure. &nsulation in

po5er transformer is tested by t5o met*ods/

1' olari3ation &nde9 (PI) of &nsulation%esistan+e (I )

"' iele+tri+ insulation fa+tor test (Tan delta)measurement.

2*is paper deals 5it* dis+ussion of t*e dissipationfa+tor measurements t*at +an be +arried out on t*einsulation of *i * po5er transformers durin routinemaintenan+e pro+edures. 2*is presentation in+ludest*e outlines setup of measurements and +al+ulationsare presented of test results 5it* summary+on+lusions.

" Principal Physical parameters" 1 Insulation resistance2*is test *as been t*e most usual *istori+ally, bein+alled to ;me er< t*e transformer (t*e term +omesfrom t*e firm of t*e first Me er systems).2*is test is performed on a measurin tester able to

enerate *i * +ontinuous volta es usually of !"""6t*at applied bet5een bot* diele+tri+ terminals of t*e

po5er transformer (one terminal to all t*e bus*in s >oined in *i * volta e, t*e ot*er to lo5 volta e and

round) allo5 evaluatin t*e pun+tual diele+tri+status inside. 2*e tester *as a *i * volta e testeroperatin from batteries or from t*e main. Measurin

prin+iple is based in measurin +urrent 8 volta e in a

1
mailto:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]


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+ontinuous 5ay t*at evolves as an ans5er to a volta estep.&nsulation %esistan+e 5ill be t*e 4uotient bet5eenvolta e and +urrent at t*e end of minute 1 of t*e test.2*is parameter s*ould be above a minimumnormali3ed value. &t +ontains dire+t information fromt*e diele+tri+ system status in t*e transformer, but isvery influen+ed by temperature (and s*ould betemperature normali3ed 8 +orre+ted). o, it@s usualanot*er parameter named olari3ation &nde9 ( &). 2omeasure it, t*e test is e9tended from minute 1 tominute 1", bein &, t*e 4uotient of +urrents in bot*time instants. 2*is value is no5 independent fromtemperature and s*ould be +omparable in +onse+utivetests.

min)1"(min)1(

)min1"()min1(

L

L

I I

reading IRreading IR

IP ==

(1)

" " +apacitance and issipation -actorissipation fa+tor is defined as t*e ratio of t*e real

po5er enerated by losses in a diele+tri+ divided byt*e total volta e applied to t*e diele+tri+ times t*ema nitude of t*e +urrent flo5in t*rou * it.

issipation fa+tor measurements are also +alled)tan( measurements in &nternational $le+tro

te+*ni+al Commission (&$C) and ot*er test standards.2*is is be+ause t*e dissipation fa+tor is numeri+allye4ual to t*e tan ent of t*e an le )( bet5een t*e+urrent flo5in t*rou * a diele+tri+ and a 4uadrate+urrent t*at 5ould flo5 t*rou * a loss free +apa+itor(Fi .1).Capa+itan+e and issipation Fa+tor are testin ofele+tri+al insulation *as been embra+ed by many in t*einsulation field as it provides information on t*ediele+tri+ +onstant of t*e insulatin materials as 5ellas t*e diele+tri+ losses. 2*e diele+tri+ +onstant is anintrinsi+ material property t*at influen+es t*e+apa+itan+e bet5een t5o ele+trodes at different

potential. &n turn, t*e +apa+itan+e influen+es t*evolta e radient distribution 5it*in assembly+omponents. Uneven +on+entration of *i * volta e

radients in t*e insulation, typi+ally measured in68mm, +ontributes to in+reased diele+tri+ po5er loss5*ere t*e radient is *i *er. &n turn, *i *er po5er loss*eats t*e insulation. Lo+ali3ed *ot spots may develop5*i+* start deterioratin t*e insulation t*at 5ouldeventually lead to diele+tri+ failure. o5er fa+tor is

parti+ularly re+ommended for dete+tin moisture andot*er loss=produ+in +ontaminants in transformer5indin s and bus*in s.

" . elationship between current capacitance anddissipation factor&n an ideal insulation system +onne+ted to analternatin volta e sour+e, t*e +apa+itan+e +urrent

c I and t*e volta e are in perfe+t 4uadrate 5it* t*e+urrent leadin . &n addition to t*e +apa+itan+e+urrent, t*ere appears in pra+ti+e a loss +urrent r I in

p*ase 5it* t*e volta e as s*o5n in Fi 1.2*e +urrent ta en by an ideal insulation (no losses,

"=r I ) is a pure +apa+itive +urrent leadin t*evolta e by " )A"( = . &n pra+ti+e, no insulationis perfe+t but *as a +ertain amount of loss and t*etotal +urrent I leads t*e volta e by a p*ase an le

)A"(


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less t*an ",! D of readin 5*ile for po5er fa+torvalues less t*an '" D t*e differen+e 5ill be less t*an 'D of readin .2*e values of c I 5ill be 5it*in ,! D of t*e value I for po5er fa+tor )(sin values up to 1" D and5it*in E D for po5er fa+tor values up to '" D.

&f it is desired to find t*e value of t*e +*ar in +urrentc I at a iven test volta e and fre4uen+y, it may be

determined from t*e follo5in relations*ip/C V I c = (!)

&n reality, a +apa+itor possesses bot* a series and parallel loss resistan+e as s*o5n in Fi '. 2*efre4uen+y of t*e applied volta e determines 5*i+* lossdominates, *o5ever, at lo5 fre4uen+ies (!"8 " H3)only t*e parallel losses p R , predominately eneratedin t*e diele+tri+, are enerally measured. For a

parti+ular fre4uen+y, any loss +an be e9pressed interms of eit*er a series or parallel e4uivalent +ir+uit

5it* e4ual a++ura+y. 2*e +*oi+e is a matter of+onvenien+e. 2*e dissipation fa+tor )(tan for t*eseries e4uivalent +ir+uit is definedas/

s s C R =tan ( )

2*e +onversion formulas are presented by t*ee4uivalent parallel impedan+e pC and p R /

p p C R 1tan = (7)

( ) s s s

s

s p C R

C C C

+=

+=

1tan1 ' (E)

( )

+=

+= s s

s s

s p

C R R R R

11

tan

11 ' ( )

. Significance of +apacitance and dissipation-actorA lar e per+enta e of ele+tri+al apparatus failures aredue to a deteriorated +ondition of t*e insulation. Manyof t*ese failures +an be anti+ipated by re ularappli+ation of simple tests and 5it* timelymaintenan+e indi+ated by t*e tests. An insulation

system or apparatus s*ould not be +ondemned until it*as been +ompletely isolated, +leaned, or servi+ed andmeasurements +ompensated for temperature. 2*e+orre+t interpretation of +apa+itan+e and dissipationfa+tor tests enerally re4uires no5led e of t*eapparatus +onstru+tion and t*e +*ara+teristi+s of t*e

parti+ular types of insulation used.C*an e in t*e normal +apa+itan+e of an insulationindi+ate su+* abnormal +onditions as presen+e of amoisture layer, s*ort +ir+uit, or open +ir+uits in t*e+apa+itan+e net5or . issipation fa+tormeasurements indi+ate t*e follo5in +onditions in t*einsulation of a 5ide ran e of ele+tri+al apparatus/

C*emi+al deterioration due to time andtemperature, in+ludin +ertain +ases of a+utedeterioration +aused by lo+ali3ed over*eatin .

Contamination by 5ater, +arbon deposits, bad oil,dirt and ot*er +*emi+als.

evere lea a e t*rou * +ra+ s and over surfa+es. &oni3ation.

2*e interpretation of measurement is usually basedon e9perien+e, re+ommendation of t*e manufa+turerof t*e e4uipment bein tested, and by observin t*esedifferen+es/

Bet5een measurements on t*e same unit aftersu++essive intervals of time.

Bet5een measurements on dupli+ate units or asimilar part of one unit, tested under t*e same+onditions around t*e same time, e. ., severalidenti+al transformers or one 5indin of a t*ree=

p*ase transformer tested separately. Bet5een measurements made at different test

volta es on one part of a unitG an in+rease in slope(tip=up) of a dissipation fa+tor versus volta e+urve at a iven volta e is an indi+ation ofioni3ation +ommen+in at t*at volta e.

An in+rease of dissipation fa+tor above a typi+alvalue may indi+ate +onditions su+* as t*ose iven int*e previous para rap*, any of 5*i+* may be eneral

or lo+ali3ed in +*ara+ter. &f t*e dissipation fa+torvaries si nifi+antly 5it* volta e do5n to somevolta e belo5 5*i+* it is substantially +onstant, t*enioni3ation is indi+ated. &f t*is e9tin+tion volta e is

belo5 t*e operatin level, t*en ioni3ation may pro ress in operation 5it* +onse4uent deterioration.

-ig "% $4uivalent Cir+uit for Capa+itorLosses

+p

p

s


4/8

Table 1% C%%$C2& ? FAC2 % A $% &$$$ C!7.1'. "

Test Temperature

(/+) +orrection -actor &"1" ",E"1! ", "'" 1,""'! 1,1'

" 1,'!! 1, "" 1,!!! 1,7!

!" 1, !!! ',1E

" ', '! ',7"

7" ,""

ome in+rease of +apa+itan+e (in+rease in +*ar in+urrent) may also be observed above t*e e9tin+tionvolta e be+ause of t*e s*ort +ir+uitin of numerousvoids by t*e ioni3ation pro+ess.An in+rease of dissipation fa+tor a++ompanied by amar ed in+rease in +apa+itan+e usually indi+atese9+essive moisture in t*e insulation. &n+rease ofdissipation fa+tor alone may be +aused by t*ermal

deterioration or by +ontamination ot*er t*an 5ater.Unless bus*in and pot*ead surfa+es, terminal boards,et+., are +lean and dry. Measured 4uantities may notne+essarily apply to t*e volume of t*e insulation undertest. Any lea a e over terminal surfa+e may add to t*elosses of t*e insulation it self and may, if e9+essive,

ive a false indi+ation of its +ondition.

0 Setup and Procedures tests

0 1 Insulation resistance testing2*e follo5in tests and +orrespondin 5irindia rams 5ill +ompletely test a t*ree p*asetransformer. Allo5 at least 1 minute (or 1" minutes)for ea+* test or until t*e readin stabili3es. Can betested as follo5s/Test 1% H.6 5indin s I $art*ed metal5or J netest +*e+ s all J as 5indin are internally +onne+ted/Test "% L.6 5indin s I $art*ed metal5or J netest +*e+ s all J

? 2$/ 2*ere may be lin on t*e transformer from ?$U2%AL to $A%2H,2*is 5ill *ave to be removed prior to +arryin out t*e&nsulation 2est.Test .% Bet5een H.6 5indin s I L.6 5indin s.

0 " issipation factor test use Schering ridgeissipation fa+tor is usually determined by a brid e

measurin te+*ni4ue, su+* as t*e +*erin Brid e ortransformer ratio Arm Brid e, use $L2A '""",5*i+* in+ludes po5er sour+e, standard +apa+itor and

balan+in brid e.2an elta test is +ondu+ted at 1" 6, !" H3 ACvolta e. &t is +ombined +apa+itan+e I dissipationfa+tor (2an delta) brid e.#enerally 2an delta measured in t*ree modes as iven

belo5/2ode 1% Un rounded spe+imen test (U 2).2ode "% #rounded spe+imen test (# 2) I2ode .% #uard modeConne+tions are s*o5n in -ig 3 .

4 esults and iscussions2*e tan delta issipation fa+tor test +ondu+ted as per+lause ?o. 1".1". in A? & C !7 1'. ".

-ig .% eries= arallel $4uivalent Cir+uit

* s+ s

SE*IES I2PE,A5+E

* p+ p

PA*A66E6 I2PE,A5+E


5/8

F is very sensitive to temperature. F (2an delta)values do not +*an e 5it* applied volta e. 2*ereferen+e temperature +ommonly used is '" de ree+enti radeG avera e oil temperature I ambienttemperature are re+orded 5*ile testin .&n +ase of oil filled transformer I rea+tors tan deltas*ould not e9+eed ",! D at '" C. 6alues ofCorre+tion Fa+tor K are listed belo5 in 2able 1.

!

#1 #" #.

Tan$

61

6" 6.n 6in$

7

'

# % *i * volta e 6 % Lo5 volta e7 % $art* terminal ' % Lineterminal

2egger

-ig 0% Hi * volta e 5indin to lo5 volta e 5indinand round (test 1).

-ig 4% Lo5 volta e 5indin to *i * volta e 5indin andround (test ').

#1 #" #.

Tan$

6

1

6" 6.

n

7

'

2egger

-ig 8% Hi * volta e 5indin to lo5 volta e5indin (test ).

#1 #" #.

Tan$

61 6" 6.n

7'

-ig% (a)

CAP

% DF

DETECTOR

H

G

L

POWER

SUPPLYREF

STD

HV LEAD

BLACK

BLUE

RED

CAP

% DF

DETECTOR

H

G

L

POWER

SUPPLYREF

STD

HV LEAD

BLACK

BLUE

RED

2*is mode used for testin 'terminal spe+imens (1 term I#round)

-ig% (b)

CAP

% DF

DETECTOR

H

G

L

POWERSUPPLY

REFSTD

HV LEAD

BLACK

BLUE

RED

-ig% (c)

-ig 3% implified measurin +ir+uit dia ram(25o=:indin 2ransformer 2ests).(a) 9ST % M$A U%$ %$ , #% U?BLU$(b) !ST ! :95 % #% U? %$ IBLU$(c) !ST % #UA% %$ I BLU$


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T A5S-: 2E TEST EP: T'!" M6A, 1!,7!8''" 6 t5o 5indin transformer

A2$ 1'8" 8'"1"2EAS9 E2E5T :- I5S96ATI:5

ESISTA5+E ;I5 I5!2op il 2emp / ' .' CC MB&?A2& ? 1" se+ " se+ "" se+

H68$art* 1 M '"M " ML68$art* '' M !

M! " M

H68L6 !'! M E"!M

11 "M

:I6 TESTSBrea =do5nvolta e

7! 6

Moisture +ontent 1 M2an elta ",""%esistivity at

" C'""-1" 1'

2able (1)/ data measurement insulation resistan+e

-ig 14% +urves of variation insulation resistan+e

-ig 10% Corre+tion Fa+tor (2an elta)

0,00

0,50

1,00

1,50

2,00

2,50

3,00

3,50

10 15 20 25 30 35 40 45 50 55 60 65 70

Temperature ( /+)

- a c

t o r

( & )

20 30 40 50 60 70 8020

30

40

50

60

70

80

90

100

110

120

P-

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submission_ISTANBUL_2012.doc