Specification of the silica gel used in Transformer Breather 3

[AKassem]

It there any standards or specs. for the silica gel used in the transformer breather ( ranges 2.5-5 MVA)

such as size (in mm or mesh), shape ( spherical , ... ), water absorption capacity , loss on drying , ...

There are many products/manufacturers of blue indication silica gel. Which one could fit for the transformer application ??

specially that the transformer's manual doesn't mention any data about the silica gel.

Thank You

 

[fx007]

Just don't use the blue ones, since they are poisonous. The others are all fine. White ones that turn brownish are fine. Hope it helps....

 

[AKassem]

Thank you fx007,

I have found that blue indicating silica gel consists of cobalt chloride which is toxic and carcinogenic.

It was thus prohibited in European and American markets since 2000.

The new alternative is the ORANGE silica gel which is indicative and depends on organic substance (Methyl Violet).

Some type changes from orange to colorless , others change from orange to dark green.

 

[prc]

Silica gel (silicon dioxide) is a colorless , granular, porous material with desiccating properties, made out of sodium silicate. It can absorb 15-40% by weight of moisture depending on the relative humidity of the exposed atmosphere. 40 % absorption at 100 % humidity. Standards call for 27 % moisture absoption capacity at standard atmosphere. Some National standards for silica gel specification are British Standard 2540-1991,Indian Standard 3401-1992. Some other important properties of silica gel for breather use are-size of bead or crystal ( 4-5mm,powdery material will choke the breathing of air), should not crush easily, loss on drying at 150 C for 4 hours shall be less than 5 % by mass.

Silcagel is doped with humidity indicator ( 0.5-1% by weight cobalt Chloride) so that deep blue will turn to pink when gel is changed from dry to wet stage. This will signal regeneration (drying at 120 C for 2 hours) of gel so that moisture will not get in to transformer. It is a good practice of transformer maintenance that gel should be dried soon the color change starts and not wait for changing the color completely. In 2000, European Union declared Cobalt chloride as a hazardous material and banned its use. Methyl violet replaced the cobalt chloride as humidity indicator where color change is from orange to green or in some brands to colourless,.Some popular brands are Envirogel TM, Trockenperlen TM, sorbead orange etc.One drawback with these new indicators are that they start changing color at a humidity content of 6% by weight.