- Conservator Tank Definition: A conservator tank is a cylindrical container on a transformer, providing space for the oil to expand and contract.
- Function: The conservator tank allows transformer oil to expand when hot and contract when cool, preventing overflow and ensuring efficient operation.
- Construction: It is a cylindrical tank with an inspection cover for maintenance, connected to the main tank via a pipe that prevents sludge from entering.
- Atmoseal Type Conservator: This type uses an air cell to separate oil from air, reducing the aging effect on the oil by preventing direct air contact.
- Diaphragm Sealed Conservator: This conservator uses a diaphragm to keep oil and air separate, preventing gas bubble formation that can cause insulation failure.
Conservator Tank of a Transformer
A conservator is an auxiliary tank mounted above the transformer main tank. The main function of a conservator tank of transformer is to accommodate changes in insulating-liquid volume while keeping the main tank filled under normal operating conditions.
Function of Conservator Tank of a Transformer
When the transformer warms because of load or ambient temperature, its liquid expands and flows into the conservator. As it cools, liquid returns to the main tank. The conservator therefore provides expansion space and a reserve of transformer insulating oil. It is not the pressure-relief device.
Construction of Conservator Tank
A conservator is commonly a horizontal cylindrical vessel with sealed ends, an inspection opening and fittings for filling, draining, venting and level indication. The exact construction and access arrangement depend on the transformer design.
The conservator pipe connects the lower part of the conservator to the main transformer tank, often through a gas-actuated relay. Some designs extend or shield the pipe inside the conservator to reduce the chance that settled material will return to the main tank. The breathing connection must open into the air side of the conservator. Its position and internal projection depend on whether the conservator is free-breathing, uses an air cell or uses a diaphragm. This arrangement keeps oil from entering the silica gel breather at the specified maximum oil level.
Working of Conservator Tank
In a free-breathing conservator, expanding insulating liquid reduces the air space and expels air through the breather. When load or ambient temperature falls, the liquid contracts and outside air enters the conservator tank of transformer through the breather. A dehydrating breather reduces moisture in that incoming air. Sealed air-cell and diaphragm systems allow the same liquid-volume change while limiting direct contact between oil and atmospheric air.
Atmoseal Type Conservator
In an air-cell conservator, a flexible bag is fitted inside the conservator reservoir. Nitrile rubber is one material used for these cells, but the material is product-specific. The silica gel breather connects to the air side of the cell. When transformer liquid expands, it compresses the cell and air leaves through the breather. When the liquid contracts, the cell expands and draws air through the breather. The power transformer oil remains outside the cell.
This arrangement limits direct contact between the insulating liquid and atmospheric air, which reduces the entry of moisture and oxygen. It does not make the system maintenance-free, because the cell, breather and oil level still require inspection.
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The space outside the cell in the conservator tank is occupied by insulating liquid. Vent fittings allow trapped gas outside the cell to be removed during filling and maintenance.
The cell’s inflation pressure and test procedure are set by its manufacturer; a universal value such as 1.0 psi should not be assumed.
Diaphragm Sealed Conservator
A diaphragm-sealed conservator uses a flexible membrane as the barrier between transformer liquid and atmospheric air. In one common arrangement, the conservator has two sections with the diaphragm clamped between them.
As the liquid expands and contracts, the diaphragm moves to change the liquid-side volume. A compatible magnetic oil gauge can indicate this movement. The atmospheric side of the conservator tank of transformer breathes through a silica gel breather, while the diaphragm limits direct contact between air and oil. Construction, gauge linkage, venting and filling procedures vary, so the manufacturer’s drawing and instructions control. A damaged diaphragm can defeat the separation barrier and must be investigated. Dissolved-gas behaviour, gas accumulation and bubble formation depend on the complete preservation and cooling system, not simply on choosing a diaphragm instead of an air cell.
The condition of the transformer should therefore be assessed using its specified alarms, inspections and oil tests.
