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Transformer Mountings Explained - Breather, Level Indicator and Buchholz (Gas) Relay

 CONSERVATOR: 

This is mounted on top of the oil tank. This should have oil two third of its volume and the remaining filled with air. The conservator is used to accommodate the expanded volume of the transformer oil when ever the oil gets heated up owing to loading of the transformer. Also when the oil cools down, the oil from the conservator will flow into the transformer tank.

The oil level in the conservator varies depending upon the temperature of the oil on various load conditions. Whenever the oil level reduces in the conservator, atmospheric air from outside will flow through the breather into the conservator and during this process the silica gel will absorb the moisture from the atmospheric air. When the oil level in the conservator rises, the air from the conservator will go to atmosphere through the breather. The breather will have oil to arrest the suspended impurities from the atmospheric air.


BREATHER:

The breather is connected through a small pipe line to the conservator top. The breather has dry silica gel in it, which is used for absorbing the moisture from the air when the air goes into the conservator tank. The dry silica gel will be bluish in color and after absorbing moisture will turn Pink.

DEEP BLUE Silica Gel - completely dry

LIGHT BLUE Silica Gel - partly humid.

PINK Silica Gel - saturated with moisture.


EXPLOSION VENT:

•This is also mounted on top of the transformer main tank.

•The free end of the explosion vent has a diaphragm fixed at its mouth. 

When ever the pressure inside the main oil tank increases owing to certain fault, this diaphragm gets punctured and the oil will escape through this vent, in order to prevent the tank from exploding.


OIL TEMPERATURE RELAY:

This indicates the instantaneous temperature of the oil. We can set the pointers in this relay in such a manner as to raise  an alarm at a preset oil temperature or trip the load on the transformer.


OIL DRAIN VALVE:

This is used for draining the oil from the main tank. This can be used for oil sampling also.


Fins:

The oil while flowing through the fins gets cooled.


Level Indicator:

• In conservator tank, a light weight hollow ball or drum floats on the transformer insulating oil. The float arm is attached with bevel gear.

• Naturally the position of the float goes up and down depending upon the oil level in the conservator and consequently the alignment of float arm changes, the bevel gear rotates.

• This movement of bevel gear is transmitted to the pointer outside the conservator, as this pointer is magnetically coupled with the bevel gear. The pointer of magnetic oil level indicator is also incorporated with a mercury switch. 


Buchholz (Gas) Relay

•The Buchholz protection is a mechanical fault detector for electrical faults in oil-immersed transformers. The Buchholz (gas) relay is placed in the piping between the transformer main tank and the oil conservator. 

•This consists of two floats, each float activating a mercuric switch. Whenever there is an inter turn short in a phase winding, there will be additional heat generated in the winding resulting in increased oil temperature and generation of oil vapor.

•This oil vapour, being light, travels from the main tank to the conservator, en route operating a float which will tilt and close a mercuric switch meant for raising alarm.

•Whenever there is a major short inside the transformer winding, the oil in the transformer gets instantaneously over heated, and thereby causing large amount of oil vapour-generation. This oil vapour, at a high velocity, gushes through the Buchholz relay, tilting another float to close the other mercury switch meant for tripping the HT supply of the transformer.

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