One of the most common transformer problems is the presence of corrosive sulfur in insulation. No matter the source of this sulfur, it disrupts the operation of the entire electrical equipment system. GlobeCore has come up with an efficient solution to remove corrosive sulfur from transformer oil.
The impact of corrosive sulfur on transformer condition
Sulfur causes corrosion. Different metals have different resistance to corrosion. The least stable metal used in transformer design is copper. If corrosion occurs in transformer oil, it generates organic acidic soaps, which increase dielectric loss and accelerate oxidation. Contact resistance also increases, causing transformer to overheat.
Organic sulfur compounds and increased temperature also increase the solubility of water in oil. Elevated temperature, in turn, accelerates the corrosion process, and the oil oxidizes faster. The deterioration of oil and metals in the transformer are connected by the positive feedback process, with negative consequences causing more consequences. Beside the damage to the transformer, it is worth noting that sulfuric compounds are harmful to the environment and personnel.
It is important to understand that certain unfavorable conditions, such as large moisture content, promote the corrosive impact of sulfur.
As the concentration of sulfur increases, so does the corrosion.
Metal sulfides form a sediment on the transformer solid insulation, reducing the dielectric properties of paper. Current leaks or short circuits are the results. Such problems are possible when copper sulfide sediments on the surface of insulation materials, such as ceramics of cellulose.
Corrosive sulfur formation and the process of corrosion
Sulfur in transformer oil is initially a component of crude oil the transformer oil is made from. The original content of sulfur in the product varies. There are vegetable based dielectric oils, but most insulation oils now are made from crude fossil oil, which may contain from less than 0.5 to over 2% sulfur. Some types of crude contains as much as 14% sulfur.
The process of corrosion occurs as follows: sulfur compounds form a complex with metals in the form of a thin film on the metal surface, which temporarily protects the metal from further deterioration. With time, this film dissipates under the influence of the oxidation products and oil temperature.
Desulfurization of transformer oil
The conclusion from the above is that to achieve high quality and reliability of transformer oil, the corrosive sulfur must be removed. There are various processes available for desulfurization of crude oil (alkaline process, hydrotreatment etc). However, acceptable results are difficult to achieve at this stage.
GlobeCore has developed a new desulfurization process. It is similar to the oil regeneration process, which is also based on adsorption. The media captures a certain range of sulfur compounds and separates them from the oil.
The adsorbent medium is loaded into special columns of a regeneration unit, which is then connected directly to a transformer. Oil passes through the sorbent and goes back into the transformer. Apart from sulfur, the process removes other impurities (acids, oxidation products etc). The oil’s dielectric strength and chemical composition are restored. Another important benefit of the GlobeCore process is the ability to reactivate saturated sorbent directly in the machine without the need to unload it.
One of the most efficient oil purification systems are the CMM-R and the UVR-450/16. GlobeCore equipment effectively сorrosive sulfur removal from transformer oil from levels 4b and 4c to 3a. The combination of regeneration of desulfurization is an excellent alternative to oil replacement, and has a noticeable effect on transformer service life extension.
