Corrosive sulfur removal

REOIL transformer oil regeneration with corrosive sulfur removal removes corrosive sulfur compounds from transformer oils. Sulfur is removed so that treated transformer oil meet the IEC 62697-1 and IEC 62535 standards. Corrosive sulfur removal is done onsite and can be performed on a live transformer. During the sulfur removal process oil is also fully regenerated.

  • Complete removal of corrosive sulfur from transformer oil
  • Service carried out on side and on live transformer
  • Safe and reliable technology

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Corrosive sulfur removal

Corrosive sulfur inside a transformer represents a risk that could lead to a failure or a complete breakdown of a transformer as was the case in a number of incidents worldwide. The cause of these failures was the growth of conductive layers of copper sulfide trough out the paper insulation as well as on other surfaces inside the transformer. It is therefore highly recommended to identify corrosive sulfur compounds in transformer oils and subsequently remove them. Corrosive compound found in transformer oil are removed in steps.

  • At the inlet of the equipment, oil is filtered through a coarse filter to prevent any particles from entering the equipment.
  • It is then heated to the desired temperature to elevate the removal effect. After the oil has been heated, it enters the back section of the equipment.
  • Oil is pumped through the back section which houses columns with sorbent media which is specifically designed to absorb corrosive sulfur molecules. It is important to note that the oil is also regenerated together with sulfur removal.
  • Oil is then pumped through a vacuum breaking valve into the degassing section where it is dehydrated and degassed.
  • Treated oil is then pumped back to the transformer by the outlet pump. After a given period, sorbent in the back section of the equipment achieves full saturation and is no longer corrosive sulfur molecules from oil.
  • At this stage, the sorbent needs to be reactivated (restored to its original state but more importantly stripped of the absorbed sulfur molecules) to be able to continue the removal process.
  • Reactivation stage starts by draining the columns in the back section of saturated oil. After the oil has been drained, a vacuum is created and maintained throughout the whole reactivation process in the back section.
  • Then by selective use of heating elements on the top parts of individual columns, the reactivation process is initiated.
  • After the reactivation process has ended a unique process inside the equipment is initiated to remove any left-over corrosive residues inside the equipment.
  • This entire process is then repeated many times until the oil has been fully regenerated and completely stripped of any corrosive sulfur compounds.

Before the beginning of the corrosive sulfur removal process, the responsible staff member always conducts an onsite inspection to ensure accessibility of the transformer and the possibility of connecting corrosive sulfur removal equipment to the transformer. Many of the main factors need to be checked and measured, such as local power source availability, flange sizes for connection, distances from and to the transformer, check valves below the conservator and any other factors that might play a role in the following corrosive sulfur removal process. After a successful onsite inspection, exact dates for connecting and disconnecting of equipment are set. At the time of the connection to the transformer, equipment is brought onsite and connected to the transformer. The connection process takes several hours to ensure that all safety requirements are fully met.

After a successful connection corrosive, sulfur removal process begins. Corrosive sulfur removal lasts for some days up to several weeks depending on the oil contamination but mainly on the total quantity of oil inside the transformer.

Once our staff determines that the removal process has been successful, the last phase of the corrosive sulfur removal process is started.  In the last step, the oil is inhibited to improve its anti-aging capabilities. Oil is then inspected in a certified laboratory to ensure that it meets the requirement of IEC 60422 standard for mineral insulating oils as well as the standard IEC 62697-1 and IEC 62535 for the presence of corrosive sulfur compounds. Equipment is then disconnected from the transformer and moved off site.

Removing corrosive sulfur is a complicated process that needs to be performed for a longer period than standard oil regeneration. The process is done on site at the transformer and can also be carried out on a live transformer. Due to the nature of the removal process oil is also completely regenerated surpassing the requirements of IEC 60422 standard. The level of contamination with corrosive sulfur is irrelevant to the treatment process, and corrosive sulfur is always completely removed from the oil. Therefore, all treated oils meet the requirement of IEC 62697-1 (Test method for quantitative determination of dibenzyl disulfide) and IEC 62535 (Test method for detection of potentially corrosive sulfur in used and unused insulating oil).

REOIL DBDS removal 400/110 kV transformer 85 000 kg of oil


Property Unit IEC 60422 Before regeneration After regeneration 5 years after regeneration
Corrosive sulfur DIN 51353 corrosive non-corrosive non-corrosive
Corrosive sulfur ASTM D 1275 B corrosive non-corrosive non-corrosive
Potentially corrosive sulfur IEC 62535 corrosive non-corrosive non-corrosive
DBDS mg/kg IEC 62697-1 110 <5 <5
Break down voltage kV/2,5 mm > 60 40 90 81
DDF at 90 C <0,01 0,0823 0,001 0,0029
Acidity mg KOH/h <0,03 0,16 0,01 0,018
Water content mg/kg <10 35 4 9
Interfacial tension mN/m >35 21 45 41

Ekofluid sees safety as one of the key factors to successful oil regeneration. It is precisely for this reason our onsite teams are specially trained to operate under strict safety guidelines to ensure maximum safety of all equipment present on site. All our personal is certified according the SCC safety guidelines. In order to maximize safety onsite our oil regeneration and oil treatment devices have implemented numerous safety features to minimize the possibility of risk. Fast closing electrics safety valves on the side of the transformer and on the side of oil regeneration equipment ensure that in case of a malfunction the transformer is completely sealed off therefore preventing any leakage of oil into the environment. Manual overheating protection inside the oil regeneration equipment ensures that in case of a software malfunction or misuse oil is not overheated and damaged. Entire oil regeneration equipment servers as an oil catch pan with level switch inside preventing of any leakage of oil into environment in case of a local malfunction of the unit. Constant monitoring of temperature, flow and vacuum parameters across the equipment ensures that in case of an unforeseen situation the equipment switches itself into a fail-safe mode. It is also very important to note that our personal never leaves the site during the operation of the equipment and therefore all our equipment is under constant supervision during its operation.

Fully automatic REOIL unit capable of transformer oil regeneration as well as corrosive sulfur removal.

Fully automatic REOIL unit working on site of the transformer carrying out oil regeneration online.

All Ekofluid transformer oil regeneration units are capable of working on location and on a live transformer.