On March 1, 2021, Paralec Energy removed the Transformer Online Filtration Unit (TRANSEC) of EGAT as the trial planned schedule. After more than a year of installation for online TRANSEC on a 200MVA transformer at Nong Chok substation, Bangkok, before the installation of the transformer, it was observed high moisture levels. Also, laboratory oil test result shows that the transformers have a moisture content of 2.35% in paper or 10-12% in oil with the calculation there are 87.6 liters of water inside the transformer. Paralec has then installed a TRANSEC, Online drying transformer.
The TRANSEC will pump the oil with low flow rate inside the transformer flowing through the tube. Then the oil will pass through the filter cylinder which contains Zeolite tablets ( that can trap and store moisture / water inside the cylinder) Then let the oil flow back into the transformer. With this process, the online drying method has more efficient over the Vacumm drying because the moisture does not be contained inside the oil, but in fact, over 90% of the moisture stay inside the paper. The calculation of the water content inside the EGAT transformer below shows the confirmation of such sentence.
During drying process, a feature of the device is built-in moisture and temperature sensors. Thanks to this, it gives us an idea of the behavior of the moisture contained inside the oil and paper. Also collected data give us better analysis. At the beginning, moisture content of the oil was 2.5-3.5 ppm fluctuating up and down. This indicates an unstable behavior and can create free water, resulting in a decrease breakdown voltage. Besides, 1-2 months later, the moisture decreased to 1.5-2ppm, but remained dynamic, for 3-4 months afterward, the moisture content reduced to 1.4-1.5 ppm and and stable.
When the online drying program has been completed. The 3 filters cylinders were brought to regeneration process to check the efficiency and confirm the filtered moisture. By the verification of water, it was found that all three cylinders contain 4.95 liters of water with 14 months of drying process.