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TRANSFORMER OIL TESTING & QUALITY :: Furan Analysis :: HGE120025 HGE120018 HGE120023 HGE120021

| Slide 1

Ling Wei Zui Komaleshwari Shahrizal Jelani Shefian

:: Furan Analysis :: >>Overview | Slide 2

>>Overview 1. Transformer is an important component in the electricity network. 2. Transformer insulation consists of the following & the performance of the transformer itself depends on the integrity of these materials eg. mineral oil, paper insulation or cellulosic materials i.e pressboard or woods 3. Life of transformer is determined by the life of its paper insulation. 4. Age of the paper insulation is determined by the mechanical strength of the paper and is measured in terms of its Degree of Polymerisation (DP). 5. Estimating DP from the oil furan concentration in particular is a non-intrusive method as it need not take the transformer out of service as it is not possible to take paper samples during running operation. 6. Therefore, the DP value is determined on the basis of cellulose decomposition products i. e. furans. These are partly oil-soluble and give some indication of the rates of decomposition of the solid insulation.

| Slide 3

:: Furan Analysis :: >>Introduction (Komal) | Slide 4

>>Introduction 1. Main objective of furan testing is to determine whether the paper in a given transformer has been or is being damaged by: • Heat • Oxygen • Moisture 2. Furanic compounds found in transformers are solely formed by the degradation of the cellulosic insulation. 3. The causes of paper to degrade from original state could be due to: • Mechanical stresses i.e internal mechanical vibration & design weaknesses reduces the paper insulation mechanical tension • Electrical stresses i.e high loading, overheating, arching & partial discharges causes paper insulation to loose its polymerisation integrity • Environmental i.e high humidity & moisture content in air around the transformer contributes to cellulose paper insulation deterioration • Type & quality of paper • Type & quality of oil • Operating condition i.e high loading or operation at maximum loading affects the paper insulation mechanical and chemical strength. | Slide 5

>>Introduction Moisture Content

Acid Number

Furans

Oil

Analysis Dissolved Gas Analysis

Dielectric Strength

Power Factor | Slide 6

>>Introduction  Furan derivatives are a measure of the degradation of cellulose paper. When the paper ages, its degree of polymerization reduces, so its mechanical strength decreases.  The degree of polymerization can only be determined directly by taking a sample of paper, a very complex operation and almost never performed in practice.  However, the degree of polymerization of the paper can be directly related to the concentration of furan derivatives in the oil. | Slide 7

>>Introduction  Furan derivate are formed as a direct result of the breakdown of the polymeric structure of cellulose paper.  The content of furan derivatives is relatively easy to measure in the oil, using HPLC and is thus a way of measuring the aging of the paper.

| Slide 8

:: Furan Analysis :: >>Types & Properties | Slide 9

>>Types and Properties  Furan is a heterocyclic aromatic system consisting of four carbons and one oxygen in five membered ring with each of the carbons having a hydrogen attached, hence the molecular formula is C4H4O. Full Structure Formula

| Slide 10

Ball-Stick Model

Skeletal Formula

>>Types and Properties  The five most prevalent derivatives of furan that arise from the degradation of the cellulose that are soluble in the oil to an appreciable degree are the following:     

| Slide 11

2-Furaldehyde or 2FAL 2-Acetylfuran or 2ACF 5-Methyl-2-Furaldehyde or 5M2F 2-Furfurol or 2FOL 5-Hydroxymethyl-2-Furaldehyde or 5HM2F

>>Types and Properties

| Slide 12

:: Furan Analysis :: >>Procedure | Slide 13

>>Procedure (Sampling) Proper Transformer Sampling (ASTM D923)  The ability of insulating oil analysis to provide an early sign of a problem condition is dependent on the quality of the oil sample that is sent to the lab.

| Slide 14

>>Procedure (Sampling) Proper Transformer Sampling (ASTM D923)  Fluids with specific gravity greater then 1.0 should be sampled from the top because free water will float.  For fluids with a specific gravity less than 1.0, such as mineral-based transformer oils, synthetic fluids and silicone oils, the sample should be taken from the bottom since water will tend to drop to the bottom in these fluids.

| Slide 15

>>Procedure (Sampling)

| Slide 16

>>Procedure (Sampling) Proper Transformer Sampling (ASTM D923)  The ideal situation for collecting a sample from an electrical apparatus is 95°F (35°C) or higher, zero percent humidity and no wind.  Cold conditions, or conditions when relative humidity is in excess of 70 percent, should be avoided, as this will increase moisture in the sample.  Collecting a sample during windy conditions is also not recommended because dust and debris enter the clean sample easily and disrupt accurate particle counts.

| Slide 17

>>Procedure (Sampling)

| Slide 18

>>Procedure (Sampling)

| Slide 19

>>Procedure (Analysis)  High-Performance Liquid Chromatography (HPLC) is a reliable method to perform furan analysis on transformer oil. The standards are IEC 61198 and ASTM D5837.  Using the High Performance Liquid Chromatography (HPLC) test method, it is prerequisite that the sample is soluble in a solvent as the measured substances cannot be transferred into the gaseous phase without decomposition (by contrast to a gas chromatography). | Slide 20

>>Procedure

| Slide 21

>>Procedure (Analysis)

| Slide 22

>>Procedure  The five compounds mentioned above are separated on an appropriate column and each is detected by use an ultraviolet detector that is adjusted automatically to the appropriate wavelength for each of the five components.

| Slide 23

>>Procedure (Analysis)  IEC 61198: Method for the determination of 2-furfural and related compounds in mineral insulating oils.  ASTM D5837: Standard test method for furanic compounds in electrical insulating liquids by HighPerformance Liquid Chromatography (HPLC).  10g of oil are solved in 10 ml of pentane for the measurement. This mixture is drawn through a silica gel column by negative pressure where the polar cellulose elements (furan derivates) accumulate. | Slide 24

>>Procedure (Analysis)  After that 20 ml of pentane are flushed through the column to remove all remaining oil components. After drying of the silica gel column in a vacuum, the adsorbed furan derivates are extracted by 10ml of acentonitrile into a volumentric flask.  After flushing of the chromatograph column the extracted mixture is injected into the sample loop out of the volumetric flask and the measurement is started. The sample is pumped through a column. Depending on the kind of the furan derivates there is an interaction between the derivates and the stationary phase of the column.

| Slide 25

>>Procedure (Analysis)  If there is a strong interaction, the substance remains relatively long in the column (long retention time). If there is a weak interaction, the respective substance passes the column quicker (short retention time).  A UV/VIS detector at the end of the column can at the same time measure the intensity and the kind of the furan derivates.

| Slide 26

>>Procedure  Calibration solutions are made up for each of the components to be analyzed and there are used to standardize the instrument responses.  From the data on the standard solutions, the extraction efficiencies for each component can be calculated and corrections can be made accordingly.  The results are usually reported in terms of parts per billion (ppb).  0 – 100 ppb = Acceptable; 101- 1000 ppb = Marginal; Greater than 1000ppb = Unacceptable

| Slide 27

:: Furan Analysis :: >>Case Studies | Slide 28

>>Direct Evaluation 

Mechanical properties of insulating paper can be established by direct measurement of its tensile strength or degree of polymerization (DP).



DP are used to evaluate the end of reliable life of paper insulation.



Suggested that DP values of 150-250 represent the lower for end-of-life criteria for paper insulation.



Below 150 the paper is without mechanical strength.



Direct measurement of these properties is not practical for in service transformer.

| Slide 29

>>Analysis of Paper Insulation 

Analysis of this paper insulation for its DP value requires removal of few strips of paper from suspect sites.



This procedure can be carried out during transformer repairs.



This result of this test will be a deciding factor in rebuilding or scrapping a transformer.



Obtain a paper sample usually is not practical and often dangerous to the transformer from a de-energized.



In service transformer an alternative method has been found.



When a cellulose molecule de-polymerises (breaks into smaller lengths or ring structure), a chemical compound known as a furan is formed.

| Slide 30

>>Furan Analysis 

Measuring the quantity and types of furan present in a transformer oil sample, the paper insulation overall DP can be inferred with a high degree of confidence.



The types and concentration of furans in an oil sample can also indicate abnormal stress in a transformer, whether intense, short duration overheating or prolonged, general overheating.

| Slide 31

Furan Content (ppm)

| Slide 32

DP Value

Significance

0-0.1

1200-700

Healthy transformer

0.1-1.0

700-450

Moderate deterioration

1-10

450-250

Extensive deterioration

>10

10 End of life criteria

Predicted Degree of polymersation

218

< 250 End of life criteria

Water in paper: % Dry Weight

3.08

2.0 (max)

Water in paper: Total Litres

7.87

| Slide 38

Extensive solid (paper) insulation deterioration

| Slide 39

| Slide 40

RESIDUAL SLUDGE BY PRODUCTS OF OIL OXIDATION

| Slide 41

>>Conclusion • The use of furanic compounds can greatly aid in the assessment of the condition of the solid paper insulation which is useful in analysis of incipient fault condition and causes of failures. • Some of the furanic compounds have sufficient stability in transformer that they may provide useful information about the long term aging of the cellulosic insulation. • Furan analysis enables test to be carried out without affecting the operation of the transformer

| Slide 42