ANALYTICAL SERVICES INCORPORATED. TJ H2b Ledicia Salgado Alfonso de Pablo

Transcription

1 ANALYTICAL SERVICES INCORPORATED TJ 2b Ledicia Salgado Alfonso de Pablo

2 Significance of Low Degree of Polymerization of Papers in Transformers Transformer 17 Torun (Poland) 9 11 May 2017)

3 SUMMARY INTRODUCTION DEGRADATION MODELS SORTCOMINGS UNCERTAINTIES IN DP MEASUREMENTS UNCERTEINTIES IN DETERMINING DP 0 ACTUAL AMOUNT OF DEGRADED PAPER TRANSFORMER TERMAL PROFILE EFFECT OF OIL TREATMENTS

4 STRUCTURE OF CELLULOSE

5 STRUCTURE OF CELLULOSE Supramolecular fibers: igh tensile strength due to extensive hydrogen bonds µm long and about 20 µm in diameter Individual fibers: About units of monomer (glucopyranose) End of life: Degree of polymerization < 200 units Tensile strength < 40% original value

6 PUBLISED DATA DP Company Reference NTPC (IN) Chakraborty 87 Alliant (US) Baldyga 150 EDF (FR) Bellesort 140 FK (C) Knab 100 TJ2b (US) anson <200 VP Diagnose (SE) Ardvidsson ydro 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 Q (CA) Duval 173 EDF (FR) Alzieu 145 ELMA (IT) Amirouche 110 EPSA (CO) Jaimes 210 Polimeri Europa De Pablo Israel Electric (IL) Grisaru

7 DEGRADATION MODELS Furans dissolved in the oil of overheated transformers were first reported by Peter Burton (CEGB) in 1982.

8 DEGRADATION MODELS Burton Vuarchex Chendong Stebbins log[2fal] = 2,5 0,005 DP log[2fal] = 2,6 0,0049 DP log[2fal] = 1,51 0,0035 DP log[2fal] = 1,5655 0,0035 DP

9 DEGRADATION MODELS

10 DEGRADATION MODELS CIGRE TF

11 DEGRADATION MODELS CIGRE TF Cellulose Furans + by products y = 30%

12 O O C O 2 O O O O C 2O O O O O CO At relatively low temperatures (<140/150 C), activation energy is relatively constant and reaction yield is close to 30% E A (A. de Pablo and B. Pahlavanpour. Electra 175, 8 32, 1997) 1/T

13 O O C O 2 O O O O C 2O O O O O CO At higher temperatures (>140/150 C), activation energy varies and reaction yield is not constant (from 40 % to 85 %) E A (B. Pahlavanpour, M. A. Martins and A. de Pablo. IEEE ISEI 2002) 1/T

14 DEGRADATION MODELS Normal Kraft vs Thermally up graded paper 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.

15 DEGRADATION MODELS Normal Kraft vs Thermally up graded paper 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,

16 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.

17 Lab DP units Remarks # As received # As received # Vacuum dried at rt # Vacuum dried at 80 C # Vacuum dried at 70 C SORTCOMINGS Uncertainties in DP measurements

18 SORTCOMINGS Uncertainties in DP measurements IEC 450:1974: 5.1 Apparatus for solution Round 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 Solution Put 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.

19 SORTCOMINGS Uncertainties in DP measurements New paper Aged paper Lab Glass balls N 2 purged Glass balls N 2 purged # # # # # # # # #

20 SORTCOMINGS Uncertainties in determining DP 0

21 SORTCOMINGS Uncertainties in determining DP 0 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 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. 7 th Int. Conf. on Properties and Applications of Dielectr. Materials, Nagoya 2003

22 SORTCOMINGS Ignorance of the actual amount of paper degraded at a given time Two unknowns: Amount of degraded paper at any time Ratio paper/oil in the transformer Amount of degraded paper at any time: 2% 10% (V. Sokolov)

23 SORTCOMINGS Ignorance of the actual amount of paper degraded at a given time Italy kv MVA Duty R Step up Step up Transmissio 26 n Transmissio 46 n Distribution Spain nowadays (distribution) kv MVA R kv MVA R < < , , , , ,23 < ,6 < , , , , ,56

24 SORTCOMINGS Ignorance of the actual amount of paper degraded at a given time

25 SORTCOMINGS Ignorance of transformer s thermal profile 110/20 kv, 31.5 MVA substation transformer 1958

26 SORTCOMINGS Ignorance of transformer s thermal profile

27 SORTCOMINGS Effect 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

28 END OF LIFE Statistics CIGRE Berlin 1993 [2FAL] ppm # transformers % < 0, ,0 0,11 0, ,9 0,51 1, ,3 1,01 5, ,3 5,01 10, ,1 > 10, ,4 Electr. Insul. Magazine 2015 Age # % [2FAL] ppm (years) transformers 90 % 95 % 99 % ,622 25,28 0,2 0,4 0, ,77 0,7 1,7 3, ,71 1,1 2 4, ,37 1,8 3,4 6,1 > ,50 2,8 6,9 26,5

29 CONCLUSIONS Relationship between DP and furfural content is not evident because: Uncertainties in DP measurements, Uncertainties in defining value of DP 0, 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.

30 CONCLUSIONS owever, 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

31 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.

32 TANK YOU VERY MUC FOR YOUR ATTENTION