How does the moisture is controlled in breather fitted on distribution transformer? Changing of breather ?

The breather is a box containing calcium chloride or silica gel to absorb moisture of air entering the conservator as it is a well

Breather of a transformer

known fact that the insulating property of the transformer oil is lost if a small amount of moisture enters in it , so dry air is allowed to pass in through this breather.

The transformer oil should not be allowed to come in contact with atmospheric air. A small amount of moisture causes a great decrease in the dielectric strength of transformer oil.

Internal Constitution of Breather

When oil level in the oil conservator changes, air moves in and out of the conservator. This action is known as breathing.

Breather contains silica gel or some other drying agent such as calcium chloride. This ensures that only dry air enters the transformer. Dry silicas gel is of blue colour. It turns pale pink as it absorbs moisture. The wet silica gel can be regenerated by drying.

Changing of Breather silica gel :-

The breather is sealed at the top with a plug. The cap nut has to be unscrewed to remove the top cap for filling fresh silica gel. Inspect the container for any visible damage or crack. Pipe up the breather to the conservator and fill the foil cup with transformer oil upto the indicated level.

Silica gel breather are usually despatched in position during transit. But in some cases, they may be despatched separately for transport purposes. In such cases, breather should be fitted as soon as possible. While fixing the breather , make sure that all joints are air-tight. Silica gel is blue colour when dry.

With absorption of moisture, its colour changes to violet and then pink. Pink colour indicates that Silica Gel is saturated and is ineffective. It should then be either replaced or reactivated. Various parts of the breather are showing below :

Various Parts of Breather

Some major point to changing of Breather :-

Remove the wing nuts supporting the body.
Glass container should be squarely fitted on its gasket, then pour re-activated or fresh Silica Gel into the container upto a level 1/4 inch from the top.
Fix the assembly to the top plate with inspection window facing outward from the transformer and secure it with the wing nuts. Ensure that top gasket is in position.
Transformer oil should be poured into the oil cup until it overflows through the screw hole and fix it to the assembly with the nut.
Silica Gel is re-activated by applying heat to it or heating it in oven unit its colour is restored to blue. While baking Silica Gel temperature should not exceed 150°C.

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