Dielectric properties of transformer oil (e.g., voltage or dielectric loss factor) can be significantly improved by filtering, degassing and removal of moisture. Only oil properly and adequately drained and filtered is suitable for transformer insulation. Often, even new transformer oil cannot be considered clean and safe for use in power systems as it accumulates pollutants during transportation.
During its use in the transformer, oil absorbs moisture, dirt particles, fibers, soot and other products of aging. Purification removes solids, free and dissolved water and dissolved gases from transformer oil. Purification also increases oil viscosity and dielectric loss tangent.
Purification is a complex procedure of removing the above contaminants to acceptable levels.
Research reveals the serious problems that arise with the contact of oil and moisture. Constant monitoring is required to identify and correct the issues in a timely manner. Analysis shows that 99% of poor dielectric strength indications are due to negligent sampling and test method selection.
Regarding the main issue of transformer oil purification, not so long ago, when diagnostics indicated high moisture content and other contamination, the following measures were taken:
- Subcontractors were selected to perform transformer oil purification
- Oil test results were submitted to the subcontractors
- A purification technique and process were selected, then a contract was signed with the subcontractor.
All of the above were not only time consuming, but also quite costly. At this time, the process of oil purification is no longer the sole area of specialized subcontracts, but can be performed by the customer onsite, using oil purification machinery.
Oil processing equipment producers offer a wide range of solutions for many applications, such as transformer oil filtration equipment, insulation oil regeneration systems, lube oil purification equipment, hydraulic oil filtration machines, turbine oil dehydration units etc.
In the last decade, such companies offer a complete systems and spare parts for transformer oil purification, available worldwide.
The process of transformer oil purification involves continuous circulation of oil through the purification system. The oil passes several coarse and fine filters, a vacuum drying and degassing section, adsorption to remove sludge and acids, etc. Besides, oil purification units are equipped with sensors to monitor oil quality at all times during purification.
Oil purification systems incorporate safety devices, such as transformer oil level sensors. These are required to automatically maintain the correct level of oil in an energized transformer when processing oil online. Oil heating is also managed automatically to prevent burning the oil, oil pressure is also controlled. The design of the units allows to perform oil processing so as not to pause or otherwise disrupt operation of power systems. Process rate is assessed by flow rate sensors.
The demand for oil purification units is growing, since increased loads on power transformer insulation systems require high quality and purity of the oil.
Industrial customers are only prepared to make a purchase, if the investment will pay off in the future in terms of finance and other resources. The extended service life of power systems and the oil makes in-house purification a popular and profitable solution.