impact of oil parameters on reliability

7/24/2019 Impact of Oil Parameters on Reliability

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Impact of Oil Properties andCharacteristics on Transformer

Reliability

Victor Sokolov

Fourth AVO New Zealand Technical Conference 2006


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The oil is an integral part of the

transformer

Many maintenance guides still consider the insulating

oil to e a se!arate com!onent that can e monitored

and treated se!arately from the

fluid"!a!er insulation system

#n fact$ the fluid is an integral !art of the transformer

!laying a dynamic role in the condition

of the entire system


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Fluid is the life blood of the Transformer

Effective diagnostic medium that containsAbout 70% of information

Responsible for dielectric stateResponsible for proper cooling

Dramatic factor for cellulose deterioration

Determines dielectric characteristics:PF, R,PD,FD!


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Outlook

%eliaility of new and ser&ice aged insulation isdetermined y dielectric strength of the oil

Moisture remains a critical reliaility factor in aged

e'ui!ment( )ound water with years is comingas !otential enemy

Oil y"!roducts #m!act on degradation of insulation

systems.Tra!!ing *ffect of electrical field

Oil y"!roducts dramatically accelerate thermal insulation

+ecom!osition !rocesses

,F - conducti&ity of oil determine dielectric characteristics



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Fluid determines Dielectric state of

Insulation integrity



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Reliability of ne insulation is determined

by dielectric strength of the oil

oil

pb

pb

oil

E

E

=

dielectric stress in the oil 1.8-1.9 times

more than in the pressboard.

Dielectric strength of pressboard is 3-4 times more strength of

Technically clean oil.



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Dielectric strength of transformer ma!or

insulation is considered as strength of

the oil duct o"er#under the inding$

Oil-barrier stress

AC Short duration 7-7.2 kV/mm

AC Long duration 6. kV/mm

O!erating voltage " kV/mm

#ressboard AC strength

$"%& kV/mm



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%ithstand strength of insulation

integrity of middle aged

transformer is determined and limited

by the le"el of oil

contamination ith ater and particles


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&ormal condition

characteristics'oisture in oil 2%-2 !!m

'oisture in barriers ().-2.%.*

'oisture in +inding !a!er ( ).%-). *

#articles ?Cigre ,otal m in )%% cm&

&2%%%

,otal &m in )%% cm&)%%%- &2%%%



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Positi"e '( tests and normal insulation

condition are not a guarantee for

reliable ser"ice of insulation

.nless le&el of oil !articles contamination is considered and

oil ga! is !rotected with solid insulation

0actors that cannot be simulated during 1V tests

Oil stirring

Rapid change of temperature

ong duration



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predominant factors

for transformer contaminated ith ater



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Particles are responsible for

dielectric state

Dr"

fibres

"

6

3

)%

)2

#$

mmEbd

)% % )%% umber

per & ml

'et

fibres

Aluminum

45 ur5 alent5ev



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(

)

*

0 ( ) * ', %

#$

mmEbd

*oisture increases particles conducti

Reducing dielectric strength

45 ur5 alent5ev



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+)0 80 (0 )0 , -.

/)

/bd/&

&0ppm

&ppm

(0ppm

10ppm

0(/

0(1

0(

0(6

3(0

-20

+harp reduction of temperature can results in

dramatic reduction of dielectric strength ofoil



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Dielectric strength of oil depends on

relati"e

+aturation due to increasing particles

conducti"ity

2il Relative saturation, %

30

30

*0

)0

(0

(0 )0 *0

,articles

20 g4to

/bd

,articles

50 g4to

9arning

Alarm

echon4 A (00*


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Free ater,repeatable failure cause

orldide

Corrosion

On the bottom



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Free ater fa"ors breakdon of

oil duct under rated "oltage



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*oisture remains a critical

reliability factor in aged

e-uipment$


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.ound ater ith years is

coming as potential enemy

&

))

)%:

37

*

"

Aging product

Bound water

Moisture

particles

5idlife Aged 6ife



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'igh Oil Temperature can add dissol"ed

ater in oil$ Release of bound ater

2bect'ater content in oil, ppm8eforeheating

After heatingat &00 for

* hours

( 5$A, &&0 #$ (9 )0

)* 5$A,&&0 #$ (3 0

&0 5$A, ((0 #$ &7 1(



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Temperature *igration of moisture

in oil contaminated ith particles

10(

0)

1&

&((&

(3

11

13

)1

)3

1

0 ) 3 &( &* (0 () (3 1(

;ours

ppm

0

&0

(0

10

)0

0

*0

70

30

t-

', ppm

;eleasing "-6 1ours Coming back 2" hours


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+tudy of effect of bound ater on dielectric

strength of oil$ 'eating up to /0C

Glasscell

Rubber

Sealing

WeightTested

oil

Electrods


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ncreasing temperature can add bound

ater 1 reduce dielectric strength of oil

Sample State Water,ppm

Breakdownvoltage,kV

1 Initial,20 1!." ##.$

A%ter &eating up to '# (2.1 $$.(

2 Initial,20 2! '$.!

A%ter &eating up to '# () #)

$ Initial,20 2' !#

A%ter &eating up to '# (( (2



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mpact of oil by,products on

degradation of insulation

properties

Oil is trans


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Type of particles

0loating in oil

n solution in oil

On sur


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2ccumulation and depositingconducti"e and polar by,products is

most likely end of life factor



27/59

Corrosi"e sulphur epidemic

!hort+circuit bet


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Degradation of dielectric properties

*an +, -esistivit/&m

aper wit&out

contamination

0.$ #31012

4ow copper sulp&ide

contamination

0.# #31010

5ig& copper sulp&idecontamination

6$07100 #310(


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+ludge ad copper sulphide sediment look

similarly

!ludge

opper sulphide


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2ttraction by field and Deposit

conducti"e sediments

Oil deca5 de!osit

Carbon de!osit


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Change of oil and paper in model parameters after

aging on ser"ice condition3$0 yearsarameter 8o 1 8o 2

rior A%ter rior A%ter

Acidit mg 95:g 0.0! 0.#) 0.01 0.1

Water solu;le acids 0.01 0.21 0.00$ 0.0(

Sludge, 0 0.0# 0 0

il


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Oil by,products contribute to

acceleration of thermal

deterioration process


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2ssessment of aging state of

operating transformer

=>$!#2(

11

? 2'$1$$#0

yearseA

DPDPLifeExpected TStartEnd +

=


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2factor describes influence of

4contamination condition4

%.%%2" %.%%2 %.%%26 %.%%27 %.%%23 %.%%2: %.%%&

)/,abs-)D

-2%

-)3

-)6

-)"

-)2

ln?

ageing

rate@

9et/acidic !a!er

=r5 !a!er

)&%oC

))%oC

:%oC

7%oC

A

Can increase ageing ten


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Predominant influence of lo

molecular acids

45 Lars Lungaard


36/59

"a#er 10 "a#er 1

Outside layers aged

more

8" !a##" van $"#

2ging decomposition of paper in


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2ging decomposition of paper in

566 *(2 7+8

9inding =# average =# outer la5ers

Seriesto! coil "2% &":

Commonto! coil %% (7

,a!to! coil 6% 2:"

,ertiar5 to! coil

o loaded

"2% &:)


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966k( 7+8 from 'ydraulic PP failure after :5 years

O"erheating the coils of '( inding

confined ithin insulating bo;

nsulation com!letel5 destro5ed


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Different life of inhibited oils

%

%%

%)

%)

%2

%2

%&

%&

%"

%"

%

% 2% "% 6% 3% )%% )2% )"% )6% )3% 2%%

time,hours

$olatileacids,

mg=2;>g

Oil F

Oil G


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Different oils gi"e different "alues of

aging characteristics

!ample Acidit"

mg =2;>g

?F

m>m

PF !ludge%

1 0.03$ 2$. 2.3% 0.014

2 0.1$4 21. 11.!% 0.01$

3 0.13 26. 4.1% 0.014

& i hibi d il i I=C d


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&ot,inhibited oil meeting I=C produce

different amount of conducti"e by,products

2@idation time ,hours

+ludge ,free life >0C

Poer Factor (s$ o;idation time


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ts a time to reconsider oil

diagnostic parameters


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Case ith ?5/ *(2 7+8 after ?6 years

#ressboard to!

inside la5ers =#H3):I outside la5ers-=#H::

#ressboard bottominside la5ers =#H3&)I outside la5ers-=#H66)

Aging rate o< outside la5er is 2.& times


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Case ith ?5/ *(2 7+8 after ?6 yearsOil !arameters meet S!ec

Li


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Parameters that characteri@ed

the oil aging state

Speci%ied parameters Additional parameters

Acidit

In&i;itor contentI


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Consider ade-uate oil

temperature during operation

'ean +inding above ambient- 6C

'ean +inding above to! oil &%C

,o! oil above ambient &C'a>imum to! oil at &%C 6(7-3%C

t is t5!ical to !ermit to! oil tem!erature u! to 7-3%C

Oil is cooling medium Some to! coils and leads ma5 have

rise o< tem!erature above oil $"%-%C


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Top oil is a mi;ed temperature from flos

through indingAcore and bulk of oil

'i>ed

'i>ed

2

)

&


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*aintaining inade-uate oil temperature

results in unnecessary aging

;ise o< to! oil above ambient

;ise o< to! coils above to! oil

=ro! o< to!/bottom tem!erature in the cooler=ro! o< oil tem!erature in a>ial duct

9inding time constant

2:

"C

"&%C

& min

,o! oil tem!eratureOil tem!erature entering +inding

Oil tem!erature leaving +inding

9inding to! coils tem!erature

3076

&0*

&(

*06

36

)%

Case +ith )37 'VA SB trans


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8nderestimation of top coils

temperature


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PF and conducti"ity of the oil

Determine "alues of dielectric

characteristicsB

PFA RA PDCA FD+


52/59

Consider factors that impact on

dielectric parameters=ielectric res!onse o< contaminated insulation de!ends

on insulation com!osition

Sensitivit5 o< dielectric !arameters to solid insulationdeterioration de!ends on relative !ortion o< solid insulation

and relative ca!acitance o< the s!ace

,he


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Typical models of oil,barrier

structure

8et


54/59

Dielectric response of pressboard barriers depends

on relati"e share of cellulose in the space

$ariation of =p 07BB01


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8nderestimation of oil parameters

results in rong diagnose#0 o< oil at "%C &*

#0 o< !ressboard %.*

!HoH %.

#0 ?C 1-L@ ).7 *

Looks like +et insulation


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=stimation of moisture content through

tan delta

p

LVHVp

K

K 00 tantantan

=

Assuming % H ! H%. ?22%-&&% kV@

tan% at 6%CH%.2*

,ested tand1V-LVH%.*+e havetan# H%.3* at 6%C

and moisture content '

&3%

p

LVHVp

K

K 00 tantantan

=


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Conclusion%eliaility of new and ser&ice aged insulation isdetermined y dielectric strength of the oil

Aging water and )ound water in oil with years is coming

as !otential enemy

Oil y"!roducts #m!act on degradation of insulation

systems

Oil relati&e saturation and !articles are main factors

+eterminated short term reliaility


58/59

Conclusion

#ts a time to reconsider oil classification of the asis

of o!erating tem!erature range

,F - conducti&ity of oil determine dielectric characteristicsAnd should e considered as for traditional ,F and

%esistance as well and no&el ,+C and F+7

#t s time to reconsider oil diagnostic characteristics


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Thank you

impact of oil parameters on reliability

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