transformator - end-of-life management of power...

END-OF-LIFE MANAGEMENT OF POWER TRANSFORMERS. METHANOL AGAINST FURANS

Laboratorio de Análisis para la Industria Energética


Cellulosic paper degradation: • Tensile strength • Folding resistance • Tear strength • Burst strength • Changes in electrical properties

But no in transformers in service due to paper inaccessibility from outside


“While the emphasis on the physical and electrical properties is justified, the omission of the much more fundamental evaluation of the molecular level properties such as chain length has been a drawback because true aging is related to the deterioration of the polymer chain. Thus, if we state that loss of 50 percent of the initial tensile strength is the ˈend of lifeˈ, there is no clear understanding of the degree of aging, though for practical purposes the limit may indicate the loss of useful tensile property to the minimum acceptable level” T. V. Oommen and L. N. Arnold, Cellulose insulation materials evaluated by degree of polymerization measurements, Proc. 15th Electr. Electron. Insul. Conf. 257-261 (1981)


W. G. Lawson, M. A. Simmons and P. S. Gale

IEEE Rrans. Electr. Insul., Vol. EI-12, 61-66 (1977)

T. V. Oommen and L. N. Arnold

Proc. 15th Electr. Electron. Insul. Conf., 257-261 (1981)


Chemical markers of paper degradation: • Carbon oxides

• Furfuraldehyde

• Methanol


Y. Bertrand, C. Tran-duy, V. Murin, A. Schaut, S. Autru and S. Eeckhoudt. CIGRE 2012. Paper D1-103

MeOH (CH3OH)


M. Ryadi, A. Tanguy, J. Jalbert and C. Rajotte, CIGRE SC A2 & D1 Joint Colloquium 2011, Kyoto, Japan. Paper PS2-O-4


A. Schaut and S. Eeckhoudt, CIGRE 2012. Paper A2-107


M. Ryadi, M.-C. Lessard and J. Jalbert, TecCon North America 2017.

Marker a B

H2O (IEC 60422) 2.24 0.04

H2O 2.59 0.04

CH3OH 2.06 0.04

C2H5OH 1.65 0.03

2-FAL 1.23 0.01

Correction factor as per water in IEC 60422


Y. Bertrand, C. Tran-duy, V. Murin, A. Schaut, S. Autru and S. Eeckhoudt. CIGRE 2012. Paper D1-103.


0

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DP

un

its

[2-FAL] (mg/kg)

CHENDONG STEBBINS

Furfuraldehyde (2-FAL)


OO

O O

O

H

HO

H

H

CH OH2

CH OH2

H

HO

H H

HO

H

HH

OH

H

O CHO

30%


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DP

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its

[2-FAL] (mg/kg)

De Pablo 2% De Pablo 5% De Pablo 10%


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[2-FAL] (mg/kg)

CHENDONG STEBBINS De Pablo 2% De Pablo 5% De Pablo 10%


End-of-life

D.H. Schroff and A. W. Stannett, IEE Proc., 132, C, 6, Nov 1985


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[2-FAL] (mg/kg)

CHENDONG De Pablo 2% De Pablo 5% De Pablo 10%


Case History – 25 MVA – 132/11 kV – ONAN – mfg 2008

Date H2 CH4 C2H6 C2H4 C2H2 CO CO2

22/09/17 14 14 14 17 0 541 7735

22/12/17 17 17 16 21 0 941 16743

24/08/18 20 20 19 22 0 913 21307

Date 2-FAL 5-HMF 2-ACF 5-MEF Sampling Temp.

22/09/17 7.26 0.14 0 0.11 30°C

22/12/17 13.91 0.22 0.17 0.28 45°C

24/08/18 12.42 0.24 0.16 0.33 72°C

Chendong: DP = 105


EUROPE - 6 laboratories- 5.005 transformers

Concentration Transformers

< 0,10 ppm 2.700 (54,0 %)

0,11 – 0,50 ppm 1.347 (26,9 %)

0,51 – 1,00 ppm 415 (8,3 %)

1,01 – 5,00 ppm 466 (9,3 %)

5,01 – 10,00 ppm 57 (1,1 %)

> 10,00 ppm 20 (0,4 %)

A. De Pablo et al., CIGRE Symposium Berlin 1993. Paper 110.09


D. Urquiza, B. García and J. C. Burgos, IEEE Electr. Insul. Magazine, 31(4), (2015)

Chendong DP = 25; De Pablo 2% DP = 27 De Pablo 5% DP = 64; De Pablo 10% DP = 119


B. Pahlavanpour, M. A. Martins and A. de Pablo. IEEE ISEI 2002

E A

1/T

Between 90°C and 150°C, activation energy is relatively constant and reaction yield is close to 30%

At higher temperatures (>140/150°C), activation energy is not constant and reaction yield increases up to 83%

A. de Pablo and B. Pahlavanpour. Electra 175, 8-32, 1997


Estimation of transformer remaining life


Reasons for transformers end-of-life other than high furans content

Cupper sulfide deposits

Although Cu2S lowers the PD-initiation level, depositions of copper sulphide on the windings alone are not sufficient to create a short circuit or partial discharge between two turns.

J. Hajek, M. Dahlund, L. Pettersson and G. Bennstam, ABB Review 61-63 (2004)



Switching transients

When a transformer is switched into or out of a system, the transient voltage produced at the terminals of the transformer may contain several high frequency oscillatory components. When this oscillatory transformer terminal voltage has a frequency component near one of the natural frequencies of the transformer and is of sufficient magnitude and duration, permanent damage to the transformer internal insulation structure may result

IEEE Std. C57.142



Lightning impulses

S. P. Balaji et al., IEEE Trans. Dielectr. Electr. Insulation. 18, 2069-2073(2011)



Lightning impulses

W. Sima et al., IEEE Trans. Dielectr. Electr. Insulation. 21(4), 1933-1940 (2014)

Sample number Applied times for the time Interval of 80 s

Applied times for the time Interval of 100 s

1 1183 1248

2 841 1032

3 1272 1459

4 1033 1282

5 1255 1317

Average 1116.8 1267.6

Applied times of OIP samples before breakdown occur with the time Interval of 80 s and 100 s


CONCLUSIONS

Methanol is a promising cellulose degradation marker, but much work is needed to understand some weaknesses of this method (is valid only for the first stages of degradation? How does its dependence on temperature affect the diagnosis? Are there more degradation models other that that of Bertrand?)


CONCLUSIONS

Furfural has been used as cellulose degradation marker for almost 40 years now. However, from the review of several databases, it seems that the widely used Chendong formula does not works because it does not considers the actual amount of paper that is being degraded at any time. How to solve this shortcoming?


CONCLUSIONS

To determine the end-of-life of a transformer, one trick could be to assume that ageing factor is constant all the life of the transformer. Then, the ratio of the consumed life to the total life leads to the residual life


CONCLUSIONS

However, it is important to note that there could be other degradation mechanisms that no necessarily produce furans or alcohols and, thus, paper degradation can not be traced with the aid of chemical markers. These mechanisms are: • Contaminants (i. e., copper sulfide deposits) • Switching transients • Lightning impulses.


THANK YOU VERY MUCH FOR YOUR ATTENTION

transformator - end-of-life management of power...

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