First step in the transformer oil purification
The first step in this serial process is to raise the oil temperature to a desired level, generally upto 65 Deg C. This aids to give the oil latent heat which later aids to dissociate the moisture and gases from oil in the degassing chamber. Additionally, the viscosity of the oil drops which aids in better filtration to some extent. Recommended heater design should consider an area of heating of about 1 to 2 W/sq.cm. In the transformer oil purification plant, the heating system is protected against over pressure built up and excess temperature rise.
Second step of transformer oil purification
The second step of transformer oil purification plant is removal of sludge and dirt from the transformer oil.
Field testing of Dielectric strength (BDV) of the Transformer Oil should be carried out in accordance with the provisions of IS 6792 & IS 1866 at regular interval during filtration job. The readings must be submitted to EIC for acceptance before stopping the filtration job.
The BDV test shall only be conducted after giving sufficient time for the oil to settle down after stoppage of the filtration process. Min BDV Value after completion of filtration and cooling down of oil should be min 60KV using 2.5mm gap electrode as per IS 6792 & PPM should be less than 20.
Removal of all suspended particles such as dust, rust, scales, colloidal carbon oxidation sludge etc. up to < 1 micron. Degassing and Dehumidification of Transformer Oil under vacuum. Circulation of heated Oil and Filling of treated oil in Transformer tank. De-acidification by evaporation and adsorption method.
OIL TRANSFER & CIRCULATING SYSTEM
Mainly consists of inlet pump (Gear type positive displacement), Outlet pump (positive displacement Gear type or Multistage Centrifugal) and necessary valves & piping to ensure easy operation and maintenance. Complete system is vacuum tight to have a leak -proof operation.
FILTRATION SYSTEM
It is suitable for removing suspended particles such as colloidal carbon, oxidation sludge, dirt, rust, scales up to < 1 micron. It consists of PRE FILTER and FINE FILTER.
PRE FILTER
It is a metallic strainer with magnet. It removes magnetic and coarse suspended particles and to protect inlet pump from damage due to abrasion.
FINE FILTER
Removes all suspended particles up to < 1 micron. Filter Elements are either non-hygroscopic molded cellulose cartridges or cleanable (with reverse airflow) edge type filter candles. Filter cartridges are easily replaceable. Additional Intermediate filter can be provided to increase life of fine filter.
DEGASSING & DEHYDRATION CHAMBER
It is designed to remove large portion of dissolved impurities (Including Moisture) from oil. Oil dispersing systems are provided to have sufficient exposure of oil to vacuum during filtration. Oil level is controlled with float switch.
VACUUM SYSTEM
Rotary oil-sealed vacuum pump or combination of Mechanical Booster Pump and Rotary oil-sealed pump is provided to get proper working vacuum during filtration. Necessary valves for easy operation and maintenance of the plant.