Page 13 - North American Clean Energy January/February 2020 Issue

The second stage deserves a more in-depth look. Adsorbents are natural
or synthetic materials that absorb contaminants from the oil on contact. Transformer oil regeneration works well with a porous absorbent called fuller’s earth*. Oil is pumped through a layer of fuller’s earth, which traps contaminants in its granules, removing both soluble and insoluble sludge from the transformer
oil. Sludge can be especially dangerous because it concentrates in the solid insulation, and its acidity is much higher than that of the oil.
In the third stage, the oil is pumped into a vacuum chamber with activator elements to increase the contact surface area of the oil. Heat and vacuum
extract water and gas from the oil. Figure 1 shows two samples of the
same transformer oil before and after regeneration. The color of the oil has been restored. Laboratory analysis confirms that oil quality parameters (acid number, dielectric strength, water and gas content etc.) are just as good as those of new oil (Table 1).In the fourth stage, the oil goes into a tank for mixing with an antioxidant additive.
When the adsorbent becomes saturated with the contaminants, it can be recycled. Saturated fuller’s earth can be reactivated and used again and again, up to 300 times. The reactivation process clears the pores of the adsorbent, extracting and removing the contaminants into a special collection vessel. After the adsorbent
is completely exhausted and cannot be reactivated, the process is performed once more to remove any remaining oil - the deactivated former adsorbent can then be used as a construction material or soil conditioner.
It is important to note that oil regeneration not only improves the oil, but also cleans the transformer (including noticeable restoration of solid insulation performance).
Transformer oil regeneration is a powerful tool for waste oil recycling. The economics and efficiency of the process stand out among all other methods. Regeneration saves the costs of oil replacement (the cost of the regeneration process is 40-70 percent lower than
the cost of new oil). It aids transformer maintenance by improving transformer reliability and, if done correctly, does
not create waste for disposal or storage. Instead, it allows insulation oil to be restored to good as new condition so it can be reused for insulation and cooling. Moreover, combining the regeneration system with special transformer protection devices (Transformer Safety System) makes it possible to regenerate oil in energized transformers. This eliminates power outages, and makes transformer maintenance easy - with no need to drain oil.
Frank May is a field service engineer at GlobeCore in Oldenburg, Germany. He has more than 30 years of practical experience
in testing, commissioning, and maintenance of industrial equipment. He’s currently researching electrical insulation oil purification and regeneration to improve transformer reliability and extend service life.
GlobeCore /// globecore.com
*The English word “fuller” originally meant a textile worker cleaning or “fulling” wool. “Earth” refers to the materials used by the fullers in their work. These materials were mostly minerals based on montmorillonite, which is known to have been used in Cyprus to clean wool as far back as 5000 B.C.
North American Clean Energy
13