Silica gel is produced synthetically from sodium silicate, which is a porous but granular form of silica. It is utilized as a desiccant or moisture adsorbent to manage humidity levels locally in order to avoid degradation of the goods. Silica gel blue crystals are known as self-indicating type desiccants and are prepared by infusing white silica crystals in cobalt chloride. These crystals are hard in nature and are placed in a breather because of their quality of absorbing moisture considerably.
The breathing process of a transformer includes in and out the flow of air due to thermal contractions and expansions created because of oil inside it. This process is important because it controls the air pressure inside the transformer. But during breathing process moisture and dust enters the transformer and this can change the dielectric strength of the oil, which in turn can disturb the proper functioning of the transformer, Sometimes leading to the failure. Therefore is particularly required that the air inside the transformer should be free from dust and humidity. This is the reason why we require a desiccant or indicating silica gel blue for breather transformer. Silica gel blue crystals are semi-transparent and glassy. When these beads or crystals of silica gel blue are free from humidity they are dark blue in color because of cobalt in them. As the humidity increases around them, their color changes from dark blue to light blue and then gradually to pink, indicating that humidity level has touched the peak and they need to be regenerated or replaced.
Deep Blue Silica Gel indicates that it is completely dry. Light blue color indicates the 15% absorption of moisture and pink color points that it is fully saturated by absorbing moisture which is about 30%-40% of its weight. Indicating silica gel can be regenerated by reheating it.
The silica gel blue beads are supplied in small pouches and in bulk both. But generally, silica blue crystals are supplied in bulk quantities only.They are available in mesh sizes of 9-12mm(1-2), 6-8 mm(3-4), 4-6mm(5-8), 2-4mm(9-16),1-2mm(16-30).The larger sizes mesh generally ranging from 1-2 Mesh, 3-4 Mesh & 5-8 Mesh are used as silica gel Breathers in transformers and the smaller i.e. 9-16 Mesh, 16-30 Mesh, 30-60 Mesh are utilized as desiccants absorbents in the form of pouches. The use of small particles as desiccants is essential as the little space between them avoids the humidity to intersect between the silica gel blue crystals, which increases its life span.