Breather delivers an economic and efficient means of regulating the level of moisture entering electrical equipment during the change in volume of the cooling medium and/or airspace caused by temperature gradients.
Breathing is a process where the transformer Breather-In or Breather out the air from its body due to thermal contraction & expansion of oil mass. When the transformer is loaded or unloaded, the oil temperature inside the transformer tank increases or decreases accordingly the air pressure in the tank changes by either breathing in or breathing out the air. This phenomenon is called Breathing of the transformer. Now, the air which is being breathed in contains either dust particles or humidity that change the dielectric strength of the oil. For proper functioning of transformer, it is necessary that dielectric strength of transformer oil remains unimpaired. Hence, it is necessary that, the air incoming into the transformer is free from moistness & dust particles.
The sole function of Silica Gel Breather is to dry out moisture & remove dust particles of the air inhaled in by transformer.
Silica Gel (Air dehydrating) breathers are transparent hollow cylinder tubes which contain chemically pure silicium salt (Silica Gel) with cobalt indicator. This grade of Silica Gel is called as “indicating grade” of Silica Gel. The indicating grade of Silica Gel, which is filled in the breather, is hard blue crystals, which has considerable absorption power for moisture. Silica Gel absorbs moisture signalling the saturation degree by changing colour as follows.
ORANGE Silica Gel completely dry
YELLOW Silica Gel partly humid. (Absorbed water for about 15% of its weight)
DARK GREEN Silica Gel saturated with moisture. (Absorbed water for about 30 - 40% of its weight)
For proper functioning of transformer dehumidification of Silica Gel crystals & removal of dust particles from breathed air is necessary Moisture is removed from Silica Gel crystals by heating it inside a ventilated oven at to 150 C, until the colour becomes deep blue again. Dusts particles are filtered by the oil in the oil cup.Pressure value for air passage into the breather are: 0.003 Kg/cm inlet or 0.005 Kg/cm outlet.
Keeping in view the above functions of Silica Gel Breather the main criteria for selecting the breather becomes
Leakage of air will lead to entrance of air with moisture & particles in the transformer, which ultimately may lead to formation of spark, and short circuit in the transformer.