Oil filled transformers 'breath'. As the temperature increases, volume of oil increases and when temerature goes down, its volume decreases. So, during expansion, volume of oil increases. As a result, air, present inside the transformer tank is displaced by oil. Now, this air has to be evacuated from the tank. Otherwise, the air will get compressed which will result in increased pressure inside the tank. To make way for the air to the atmosphere, a pipe is provided from the top side of the conservator. Displaced air passes to atmosphere through this pipe. While volume of oil decreases, air enteres from atmosphere through this pipe.
A "breather" is provided at the end of the pipe from where the air enters/exit into/from the transformer tank. This breather is a chamber filled with silica gel which can absorb water ( moisture), that may be present in the air. Air must be free from moisture while it enters the transformer. Presence of moisture may contaminate transformer oil. Contaminated oil may, in turn, damage the insulation - by bringing down the value of insulation resistance
There is a cup at the bottom of the breather. This cup is filled to a certain level with transformer oil. Air exits/enters through this oil. Oil is provided as an extra filter.
The bubble that we saw in the vedio clipping of the Breathing action is the exit of air from the tank through the silica gel and then through the transformer oil in the cup.
Please note that the pipe which is called the breather pipe will not carry any oil. This is meant only to carry air.
There are certain small capacity transformers that are completely sealed. There will be no conservator in these transformers. These transformers are filled with transformer oil to a certain level and the remaining part of the tank will be filled with nitrogen. While transformer oil expands, pressure increases. Due to pressure, nitrogen dissolves in the oil. This neutralises the pressure. While oil cools down, nitrogen will be leberated from the oil and thus complimenting the decreased pressure.
This article is contributed by Sri. Natesan P. P.