Transformer Oil Analysis

Laboratory develops the following analysis methods and standards:

Step One - First Analysis:

DGA is use as a tool to identify incipient faults or problems in oil filled power transformers.

The use of DGA as a powerful diagnosis tool is a critical and important aspect of determining the condition and health of a transformer.

There are different methods for the interpretation of the results:

  1. Typical faults described in UNE EN 60599

  2. Gas ratios method, including Rogers Code

  3. Duval Triangle method

  4. And sometimes, Gas Pattern Method

-Sulfur contained in insulating oil may range from .001 to 0.5% - Forms ( in increasingorder of corrosivity)

  1. 1. Thiophens

  2. 2. Disulfides and poly sulfides

  3. 3. Thio-esters

  4. 4. Mercaptans

  5. 5. Elemental sulfur

- Disulfides appear to be the most commonly occurring corrosivity causing compounds.

- DBDS has been identified as culprit in number of cases where failures have beenattributed to corrosive sulfur in oil.

- Can measure with a gas chromatograph with an elemental specific detector based onatomic absorption spectroscopy (GC-AED).

Triazoles (BZT&TT)

- Passivation is a term used in corrosion science to describe the formation of nonpermeableprotective layers on metal surfaces.

- The formation of such layers prevents corrosion and dissolution by decreasing theexchange currents between the electrolyte and the metal.

- Passivators - thus create a chemical layer that protects the copper from the oil, andthe oil from the copper.

- This prevents formation of oil soluble copper complexes that can catalyse oiloxidation.

- The protective layer thus fills two functions; to prevent direct copper transport andto prevent formation of corrosive oil oxidation products.

- In the electrical industry the organic passivators most commonly used arederivatives of benzotriazole (BTA). The methyl-substituted variant known astolytriazole (TTA) is slightly more oil soluble than BTA. But only when it is madesignificantly less hydrophilic by N-aminomethylation does it becomes fully misciblewith oils (One such example is Irgamet 39™ -CIBA Specialty Chemicals).

- Sulphur present refined as sulphur-containing is in oil sulphur molecules.

- The amount depends on oil refining processes, degree of refining and crude oiltype.

- Due to poor refining or contamination, reactive compounds giving corrosion atnormal operating temperatures may be present.

- They are detected by standard tests:

* ASTM 1275 Method B

* IEC 62535.

Furfural and Related Compounds (IEC 61198)

- Specifies test methods for the analysis of 2-furfural and related furan compoundsresulting from the degradation of cellulosic insulation and found in mineral insulatingoil samples taken from electrical equipment.

- The compounds are analysed by high performance liquid chromatography. Prior toHPLC analysis, furan derivatives are extracted from the oil by use of a suitable extraction method such as liquid-liquid extraction (method A) or solid-phaseseparation on a silica cartridge (method B).

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