thread238-5777 On Line Transformer Oil reclamation

[RohanaE]

Velcon Systems too supplied on line transformer dry out system with patented filtration product. But the product is recommended for removal of dissolve water and different filter element is recommended for cost effective removal of free water. When analysing oil for moisture content (say using Domino Doble)the measurement is for total water content. Can we distinguish the two separate measurements. Has anyone have the experience with Velcon system?

 

[prc]

I dont know whether the on-line system you mentioned is a filteration system or reclamation system.Normally these are on-line filteration systems with a small volume of oil flow through it.It will remove moisture and particles.It will be removing total water from transformer.Many transformer experts doubt its efficacy mainly due to the small amount of oil handled compared to total oil content in equipment.If the transformer too wet,best way is an off line filteration using a high capacity filter machine having heater and vacuum chamber.

 

[RohanaE]

The idea of on line filtering conceived as we have 4 nos 31.5 MVA similar transformers of 20 years old with following test measurements. Until year 2002-08 IR reading (at 5 kV)of these transformers were above 5000 Mohm which is comparable to commissioning values. In 2003-05 it drops to 200 Mohm and now remain at same order. The Bushings were tested and found ok. The conventional heat and vacuum treatment of oil over a period of 3 weeks in year 2003 -07 didn't improve IR readings. FR analysis was done before and after oil treatment and moisture content was measured / modelled and improvement is insignificant. (from 2.6 ppm to 2.2 ppm). The water content of oil in 2006 from dobel domino is 26 ppm. The on line oil dry out process claim to be a different process which works while maintaining equilibrium of moisture particle movement between oil and press board. any comments are welcome

 

[prc]

IR reading reduction may be due to reduction in resistivity of oil and not due to moisture alone.Please check IR at 1 minute and 10 minute with voltage application.The ratio of IR at 10 to 1 minute measurement should be above 1.3 if trf is dry.Check tan delta of winding and this should be less than 1%,and preferably around 0.5 %at 20 C.Check water content in oil,when transformer is fully loaded and oil is max hot.In cold condition water will go back to paper and you will be misled by low water content values of oil.

If you doubt the trf is wet,best way is to get an ample sized( 3000litres/hour),good condition oil filter machine with heaters and vaccum chamber.Drain bottom oil 300-400mm from bottom tank.This will be full of free or colloidal water.Dehydrate this drained oil separately and fill back.Do hot oil circulation for 5-10 passes of oil in transformer.Oil temperature in tank shall be above 60C.This will be much faster and cost effective dry out than the small on-line filters.

If trf too wet,there are still ingenious methods to dry out trf.