Transformer oil degasification
Oxygen found in transformer oil leads to oxidation and significantly reduces the dielectric strength of the oil and the insulating system. In general, under normal atmospheric pressure, the insulating oil contains approximately 10% of atmospheric air. The higher the temperature, the better the dissolution of air in oil wll be. It is highly important to understand that the composition of atmospheric air and the air dissolved in oil, differ greatly. Atmospheric air is comprised of 78% nitrogen and 21% oxygen. When that same air is dissolved in oil, it becomes comprised of 69.8% nitrogen and 30.2 oxygen.
Transformer oil degassing is a complex of processes targeted at the removal of water, gasses, and mechanical impurities from the dielectric oil. The following methods may be used for drying the oil:
- centrifugation In this case, mechanical impurities and water are removed from oil, influenced by centrifugal forces. In practice, this method is applied mainly for oils that will be used for equipment with a voltage of no less than 35 kV.
- adsorption Water and impurities are removed by using mineral and synthetic adsorbents. This method allows for the removal of water dissolved in the oil;
- vacuum drying Oil is heated up and then is pumped through a degasifier.
Vacuum processing is considered to be the most effective method since it removes dissolved water and gasses from the oil. This process is realized either by spraying oil in vacuum chambers or using special heaters that are evenly distributed in the vacuum chamber utilizing Raschig rings and grid packings. There are special oil
degassing units used to perform the degassing and vacuumizing processes.
The main part of such equipment is a degasifier that consists of two tanks. The vacuum in the tanks is created by vacuum pump system. Additionally, there are spraying devices on the tank cap that distribute oil evenly in the vacuum chamber. Oil Degassing takes place when oil flows in thin streams on the surface of Raschig rings.
The method of vacuum spraying is based on the spraying of the oil and water solution in the vacuum by a pulverizing jet into a special tank. These processes allow for the removal of free and dissolved moisture as well as dissolved air. If the level of oil dispersion is adequately thin, it easily gets rid of moisture.
Vacuum drying includes three main stages such as:
(1) breakdown voltage increases very sharply due to the removal of emulsion water;
(2) there are minor changes of the breakdown voltage of oil (60 kV) At this time dissolved and loosely-coupled water is removed; and
(3) breakdown voltage increases slowly due to the removal of bound water.
The efficiency of vacuum drying of transformer oil is improved when it is warmed up because the amount of evaporable moisture is increased.
has developed the CMM line of vacuum units for transformer oil purification to solve the problems that arise when mounting, repairing and servicing oil-filled equipment with a voltage up to 1150 kV.
To meet the needs of our customers, each unit is custom made and can be puchased in may come in pad-mounted version, or placed on single axle or tandem trailers. The technical characteristics of the CMM units are described below
The unit can be operated in three operation modes:
- air drying and heating mode
- adsorbent (other equipment filled with) regeneration mode.
- adsorbent regeneration (the unit filled with) mode – (regeneration of technical specifications of damp synthetic zeolite by means of hot air heating up to the temperature of 380 – 400 °С).
The unit pumps air, non-aggressive gases, vapors and air-steam mixtures out of the transformers and hermetical vacuum systems.
The company manufactures three types of units, which differ in components, mode of operation and specifications, but are equally efficient. First type – single module unit consisting of two-stage refrigerator, designed for generation of process cold (to negative 70оС); Second type – twin module unit with vacuum backing pump: