Transformer Oil - Classification (Colour) Status
Colour | Interpretation (from light yellow to dark brown - even coal black) |
GOOD | Oil in this classification is servicing its purpose as an insulator and coolant, and effectively protecting other classes of insulation from deterioration.
Retest in one year |
MARGINAL | Sludge is in solution and at the stage where the initial take out occurs. The void in the insulation paper are probably filled with sludge. Fatty type acids have begun to coat the internal parts of the transformer Now is the optimum time for servicing oil from a coast view point and to avoid potential damage to the insulation in the transformer |
BAD | Sludge has begun to precipitate out of the oil and accumulate on the horizontal surfaces and cooling ducts openings. This initial fallout of sludge should be removed from the transformer by thermal cleaning restoring the oil to the upper end of the good oil classification. If serviced at this time, there should be no loss in the life expectancy of the transformer. |
VERY BAD | Sludge has begun to coat the core and coils of the transformer and act as a catalyst to speed up the oxidation process. Operating efficiency and oil temperature will be affected. The acid formed will begin to attack the solid insulation within the transformer. Thermal cleaning should be done as soon as possible. |
EXTREMELY BAD | Sludge is deposited in large quantities throughout the transformer and the lower ends of some cooling ducts could be completely blocked with sludge. The possibility of a premature failure is great, and corrective action becomes mandatory. Permanent damage to the overall insulation system may have occurred at this time. Thermal cleaning is strongly recommended. |
POOR | …./…. I have seen such oil, hopefully it was in a very old design transformer (which had never been serviced) for which old techniques and old design with great quantities of materials could afford a minimum of cooling and external added insulation (given by this oil)… |
When oil in the transformer reaches this condition, the possibility of a failure is (more than) great and any reclamation (regeneration) of the oil in the transformer would have to be done with power off; Because of the large amount of sludge and high acid content, the best thing is to drain of the old oil. Flush down the internal parts of the transformer with hot oil refill with new oil and then thermal clean the transformer with the new oil. |