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ANALYTICAL SERVICES INCORPORATED
TJ|H2b – Ledicia Salgado
Alfonso de Pablo
Significance of Low Degree of Polymerization of Papers in
Transformers
Transformer 17 – Torun (Poland) – 9‐11 May 2017)
SUMMARY
INTRODUCTIONINTRODUCTION
DEGRADATION MODELSDEGRADATION MODELS
SHORTCOMINGSSHORTCOMINGS
UNCERTAINTIES IN DP MEASUREMENTS
UNCERTEINTIES IN DETERMINING DP0
ACTUAL AMOUNT OF DEGRADED PAPER
TRANSFORMER THERMAL PROFILE
EFFECT OF OIL TREATMENTS
STRUCTURE OF CELLULOSE
STRUCTURE OF CELLULOSE
Supramolecular fibers:•High tensile strength due to extensive hydrogen bonds•600 – 2.000 µm long and about 20 µm in diameter
Individual fibers:•About 1.200 units of monomer (glucopyranose)
End‐of‐life:•Degree of polymerization < 200 units•Tensile strength < 40% original value
PUBLISHED DATADP Company Reference
150‐220 NTPC (IN) Chakraborty
87 Alliant (US) Baldyga
150 EDF (FR) Bellesort
140 FKH (CH) Knab
100 TJH2b (US) Hanson
<200 VP Diagnose (SE) Ardvidsson
100‐150 Hydro One (CA) Figuerola
100 NL Salverada
75 Trafo Service (FR) François
<100 Ameren (US) Bizzoff
DP Company Reference
150 AU/NZ Wright
200 EIMV (SI) Gradnik
150 NZ Bhumiwat
170 HQ (CA) Duval
173 EDF (FR) Alzieu
145 ELMA (IT) Amirouche
110 EPSA (CO) Jaimes
210 Polimeri Europa De Pablo
50‐200 Israel Electric (IL) Grisaru
Furans dissolved in the oil Furans dissolved in the oil of overheated of overheated transformers were first transformers were first reported by Peter Burton reported by Peter Burton (CEGB) in 1982.(CEGB) in 1982.
DEGRADATION MODELS
DEGRADATION MODELS
Burton log[2FAL] = 2,5 – 0,005 DP
Vuarchex log[2FAL] = 2,6 – 0,0049 DP
Chendong log[2FAL] = 1,51 – 0,0035 DP
Stebbins log[2FAL] = 1,5655 – 0,0035 DP
DEGRADATION MODELS
CIGRE TF.15.01.03
DEGRADATION MODELS
CIGRE TF.15.01.03
Cellulose Furans + by‐products y = 30%
DEGRADATION MODELS
OO
O O
O
H
HOH
H
CH OH2
CH OH2
H
HO
H H
HOH
HH
OHH
O CHO
E A
1/T
At relatively low temperatures (<140/150 °C), activation energy is relatively constant and reaction yield is close to 30%
(A. de Pablo and B. Pahlavanpour. Electra 175, 8‐32, 1997)
OO
O O
O
H
HOH
H
CH OH2
CH OH2
H
HO
H H
HOH
HH
OHH
O CHO
E A
1/T
At higher temperatures (>140/150°C), activation energy varies and reaction yield is not constant (from 40 % to 85 %)
(B. Pahlavanpour, M. A. Martins and A. de Pablo. IEEE ISEI 2002)
S. D. Myers experts published a survey on furans formation in transformers having TU paper. They reported furans concentrations in ppb rather than ppm. This has wrongly induced to think that TU paper forms lower amounts of furans than normal Kraft paper.
Normal Kraft vs Thermally up‐graded paper
DEGRADATION MODELS
Influence of type of paper
The results of this study supported the theory that there is a relationship between the concentration of 2‐Furaldehyde and the DP of paper. There was no difference in this relationship between thermally upgraded and non‐thermally upgraded paper,
Normal Kraft vs Thermally up‐graded paper
DEGRADATION MODELS
Normal Kraft vs Thermally up‐graded paper
Lower levels of furans are formed in transformers using TU paper simply because TU paper degrades more slowly than regular Kraft paper does and therefore reaches low DPs more slowly.
DEGRADATION MODELS
SHORTCOMINGSUncertainties in DP measurements
Lab DP units Remarks
# 1 1550 As received
# 2 1500 As received
# 3 1150 Vacuum dried at rt
# 4 1050 Vacuum dried at 80°C
# 5 944 Vacuum dried at 70°C
SHORTCOMINGSUncertainties in DP measurements
IEC 450:1974:“5.1 Apparatus for solutionRound‐bottomed 50 ml flask, preferably with a short narrow neck, or a narrow‐necked 50 ml Erlenmeyer flask.Rubber stopper, fitting the neck of the flask, through which passes a capillary tube fitted with a small‐bore glass cock.Glass balls 4 mm to 6 mm diameter, which shall not be able to enter the bore of the cock.…7.1.2 SolutionPut a few balls in the flask.Add the weighed test sample.Carefully shake or stir by hand, to ensure…Add 22,5 ml of distilled water.Again shake or…Leave for half an hour to allow thorough impregnation with water.Add 22,5 ml 1 M solution of cupriethylene‐diamine.Add a number of glass balls so that, when the stopper with capillary tube, etc., is fitted, the liquid will entirely fill the flask and reach the bore of the cock.…”
SHORTCOMINGSUncertainties in DP measurements
LabNew paper Aged paper
Glass balls N2 purged Glass balls N2 purged
# 1 1206 1206 664 621
# 2 1125 1163 620 603
# 3 1214 1281 657 669
# 4 1303 1303 633 647
# 5 918 1084 494 557
# 6 1260 1215 725 665
# 7 596 1174 152 606
# 8 1197 854
# 9 1291 1387 640 658
SHORTCOMINGSUncertainties in determining DP0
SHORTCOMINGSUncertainties in determining DP0
“Finally, as mentioned earlier, use of a linear relationship between life remaining or life used and DP, with a “beginning life” value for DP of 1200 is not completely appropriate. New paper before being installed in a transformer typically has a degree of polymerization of 1200 to 1400. After factory drying and assembly, our experience is that a new paper in a new transformer has a DP of 800 to 1200, and it is usually more appropriate to figure life assessment based on changes from the lower limit of this range”
R. Stebbins et al., Proc. 7th Int. Conf. on Properties and Applications of Dielectr. Materials, Nagoya 2003
SHORTCOMINGSIgnorance of the actual amount of paper degraded at a given time
Two unknowns: Amount of degraded paper at any timeRatio paper/oil in the transformer
Amount of degraded paper at any time: 2% ‐ 10% (V. Sokolov)
SHORTCOMINGSIgnorance of the actual amount of paper degraded at a given time
Italy 1970‐1990
kV MVA Duty R
420 370 Step‐up 20
240 180 Step‐up 24
420 250 Transmission
26
220 100 Transmission
46
130 30‐40 Distribution 38‐45
Spain nowadays (distribution)
kV MVA R kV MVA R
<66 10 6 <66 65 8,6
66 10 2,6 66 65 6,3
132 10 2,5 132 65 5,23
<66 40 4,6 <66 75 8,75
66 40 4,83 66 75 6,4
132 40 5,24 132 75 5,56
SHORTCOMINGSIgnorance of the actual amount of paper degraded at a given time
661
561
384
SHORTCOMINGSIgnorance of transformer´s thermal profile
110/20 kV, 31.5 MVA substation transformer 1958
SHORTCOMINGSIgnorance of transformer´s thermal profile
SHORTCOMINGSEffect of oil treatments
• Degassing the oil partially removes furfural because furfural is relatively volatile.
• Oil reclamation with Fuller´s earths almost completely removes furfural because its polarity.
• After oil replacement may soon appear some furfural because part of the old furfural is absorbed on paper and dissolved again by the new oil
END OF LIFEStatistics
CIGRE Berlin 1993
[2FAL] ppm # transformers %
< 0,10 2.700 54,0
0,11 – 0,50 1.347 26,9
0,51 – 1,00 415 8,3
1,01 – 5,00 466 9,3
5,01 – 10,00 57 1,1
> 10,00 20 0,4
Electr. Insul. Magazine 2015
Age (years)
# transformers
% [2FAL] ppm
90 % 95 % 99 %
0 – 10 4,622 25,28 0,2 0,4 0,9
11 – 20 4.528 24,77 0,7 1,7 3,7
21 – 30 4.517 24,71 1,1 2 4,3
31 ‐ 40 3.540 19,37 1,8 3,4 6,1
> 40 1.006 5,50 2,8 6,9 26,5
CONCLUSIONS
Relationship between DP and furfural content is not evident because:
•Uncertainties in DP measurements,•Uncertainties in defining value of DP0,•Ignorance of the actual amount of paper degraded at any time,•Ignorance of transformer thermal profile•Effect of oil treatments
Low degree of polymerization observed in many transformers working correctly may be true or may be due to these uncertainties.
CONCLUSIONS
However, analysis of furans, mainly furfuraldehyde, if considered with due regard and proper engineering
judgement, constitute a very important tool to estimate transformer cellulosic paper condition
CONCLUSIONS
The End of Life (EOL) criteria, now considered to be at DP of 200 units, needs to be revised.
Lower limit does not represent a serious risk for the transformer and may assist in saving asset investments.
THANK YOU VERY MUCH FOR YOUR ATTENTION