Conservator Tank of a Transformer
Conservator tank is a airtight metallic cylindrical tank mounted on the top of the supporting structure of the transformer. It is one of the important part of the transformer.
It is vented at the top above the main tank and bushings and generally half-filled with the transformer oil to allow expansion and contraction due to change in temperature of the winding of the transformer.
Its main function is to provide the extra space for the expansion and contraction of the transformer oil due to variation in the temperature of the winding of the transformer. It is connected to the main tank through a pipe on which buchholz relay is mounted. A level indicator is also installed on it to measure the quantity of oil.
Function of Conservator Tank of Transformer
The main function of conservator tank is to maintain the oil level in the main tank by entering the extended insulating oil into the it.
When the transformer is over-loaded or other faults occurs due to which winding generates heat that increases the temperature of the insulating oil. Then, the volume of insulating oil inside main tank of transformer increases.
There used a metallic cylindrical tank called conservator tank to provide sufficient space for the expanded insulating oil. It also acts as a reservoir for the insulating oil. It is connected to the main tank through a pipe.
Construction of Conservator Tank of Transformer
Conservator tank is a cylindrical shaped oil container made up of iron closed from both ends. One large inspection cover is provided on either side of the container to facilitate maintenance and cleaning easily from inside of it.
A pipe that comes from main tank is projected inside the conservator tank from bottom portion. Head of the pipe inside it is provided with a cap because this cap prevent oil sludge and sediment to enter into main tank from the it.
A buchholz relay is also mounted on the pipe which connect it to the main tank to protect the transformer from the all kinds of internal faults that generates heat.
Generally, a silica-gel breather is mounted on the pipe enters into the conservator from top portion. If it enters from bottom, it should be projected well above the level of oil inside it. This arrangement ensure that insulating oil does not enter into the silica-gel breather even at highest operating level of insulating oil.
A MOG (Magnetic Oil Gauge) is also installed at the lower half to check the level of the insulating oil in it.
Working principle of Conservator Tank of Transformer
When the transformer is over-load or other faults occurs that causes generation of heat in winding and core due to which temperature of insulating oil increases. Then the insulating oil expand and its volume also increases.
Then, the extended volume of the insulating oil moves upward into the conservator to occupy the vacant space above the oil level inside it which is partially occupied by the insulating oil. Consequently, corresponding quantity of air of that space is pushed outside through the silica-gel breather.
On other hand when the load of transformer decreases or transformer is turned off then, the heat generation stops and temperature of insulating oil also decreases, the oil inside the main tank contracts. Then the atmospheric air enters into the conservator through silica-gel breather.
Types of Conservator Tank
There are mainly two types of conservator tank which are listed below.
- Atmo-seal Type Conservator Tank
- Diaphragm sealed Conservator Tank
Atmo-seal Type Conservator Tank
In this type, an air cell made of NBR material is fitted inside its reservoir. The silica-gel breather is connected at the top of this air cell. The oil level in the main tank rises and falls according to this air cell deflated and inflated.
When the air cell gets deflated the air inside the air cell comes out through silica-gel breather and when the cell is inflated the outside air comes in through silica-gel breather. This arrangement prevents direct contact of oil with air.
The extra space available outside the cell is totally filled by oil. Air vents are provided on the top of atmo-seal type conservator for venting accumulated air outside the air cell. The pressure inside the air cell must be maintained 1.0 PSI.
Diaphragm sealed Conservator Tank
In this type, diaphragm is used as a barrier between insulating oil and atmospheric air. In this case the conservator tank is made of two semi-spherical halves.
The diaphragm is held between the the two halves and bolted. As oil expands it pushes the diaphragm upward. The oil level indicator i.e. magnetic oil gauge ( MOG ) indicates the position of diaphragm as the rod of this MOG is connected to the diaphragm.
When the oil level falls down, the diaphragm deflects and the atmospheric air enters through silica-gel breather to fills the vacant place. Diaphragm sealed conservator tank has one advantage over air cell conservator. If gas is pressurized to a high level, it gets dissolved in insulating oil until the oil reaches its saturation point.
But the load of transformer is suddenly dropped at this state then, the temperature and pressure falls severely and insulating oil becomes supersaturated and bubbles from the gas will be evolved. If a pump is attached to the cooling circuit which helps to generate more bubbles. These bubbles can damage the insulation.
Conclusion
Hope, you have clearly understand about the conservator tank of the transformer, its function, construction, working principle and types. Make sure to leave your opinion and suggestion about this post in the comment section below.