AUTOMATIC FILTER RE-DRYING
A key advantage of the Trojan is the automatic Filter Re-Drying and the minimum 18 month life expectancy. The Filters are large capacity and have a high attraction to water, and will consistently remove water to under 1 ppm. The filters can be Re-Dried hundreds of times without any effect on performance allowing a large number of transformers to be dried without the need for Filter replacement. This significantly reduces the cost per litre of water removed compared to other adsorbent molecular sieve systems.
Oil is pumped through the Filters which remove and store the dissolved water. Depending on the transformer oil volume and cellulose water content, the Trojan is usually set by the operator to Filter for between 20 and 50 hours. A guide is provided. At the end of the Filtering hours, the Trojan stops drawing oil from the transformer, and completes the Filter Re-Dry process. A Trojan 1000 takes about four hours to Re-Dry.
The volume of water removed at each Re-Dry is recorded, and all water removed during the Re-Dry process cannot re-enter the transformer. At the end of the Filter Re-Dry, the Trojan checks the hoses and pipe work of any bubbles before re-starting Filtering for the hours entered, to collect more water. These cycles of Filtering and Filter Re-Dry continue until the Trojan is stopped.
As filtering progresses, the transformer oil and cellulose become dryer. The Trojan compensates by drying the Filter to even lower levels, which ensures that no matter how low the water in the oil ppm value, the Trojan will always remove water. If the water in oil entering the Trojan from the transformer is under 1 ppm, the Trojan Filters will still remove over 50% of the water, and return the oil to the transformer at < 0.3 ppm. The Filters will always be dryer than the water level in the transformer.
Fig.1 is an example of three 20 hour Filtering periods and two Filter Re-Dry cycles. The Filters gradually fill up (indicated by the Filter outlet ppm), water removal efficiency is restored following the Re-Dry the improved is evident.
