Transformer Oil BDV Value Changes

when working in the steelworks, we had a similar problem. Can't remember the solution but I do remember we contacted Shell Oil who were VERY helpful, give them a try.

I guess your problem relates to sludge settled at the tank bottom.

An oil cleaning plant consists of heaters as well as filters to extract sludge, your method is non-standard.

There is nothing wrong if you put oil in transformer at 75 deg C.

It seems you are extracting oil sample from the drain plug, drain a bucket of oil before taking sample or more appropriately take sample of oil from the bottom of tank by inserting a tube from the top,

As per IEC, six samples are tested, neglecting the first one, average of 5 readings is taken and if the value is 50 kV or more there is no requirement for any treatment (why you have done at 60 ?).

Dielectric mass mention on the nameplate is 883 Kg. Approximately it took 5 Drums.

We are not filtering the oil. We want to heat the oil, Bring its BDV valu to the required level and then put it back to the transformer.

BASICALLY WHAT U CALLED HEATING IS NOTHING BUT PASSING OIL THROUGH A CENTRIFUGE AND HEATING AND VACUUMING AND WITHOUT VACUUMING YOU CANNOT REMOVE MISTURE AND OTHER IMPURITIES FROM OIL BY ONLY HEATING.

THIS IS APPLICABLE FOR DRUM TO DRUM FILTRATION ALSO.

As at present we don't have any filteration equipment and oil is at present at 75 C in drums. Can High BDV (>60 KV) can be achieved without filteration at that moment.

What do you recommend

AS PER IEC THE TRANSFORMER OIL CANNOT BE DRIED ONLY BY HEATING,AND BY HEATING AT HIGHER TEMPERATURES GREATER THAN 70DEG CENTIGRADE YOU ARE AGEING THE OIL AND AS PER IER DRYING AND REMOVAL OF MOISTURE IS NOT POSSIBLE WITHOUT A FILTER MACHINE.

APART FROM THAT BY USING A FILTER MACHINE AND FILTERING THE WHOLE SYSTEM IE TRANSFORMER YOU WILL BE ABLE TO REMOVE THE EMBEDDED MOISTURE OF THE TRANSFORMER WINDING ALSO ,OTHERWISE THERE MAY AND WILL BE INTERMITTENT AND UNPREDICTABLE FAILURE.

It may be that water/moisture is migrating out of the transformer insulation as it cools and affecting breakdown voltage. Give the transformer about 3 days to heat back up and drive the moisture back into the paper. Then take your sample. Include a moisture test such as D-1533B and compare all samples, hot and cold, to see if my suggestion "holds water". Dissolved gas tests are also very useful to diagnose your transformer's health.

Mr. Aghvel Niazi,

As rightly pointed out by Mr. S. Bhattacharya, you are following an absolutely wrong procedure to improve the BD value of transformer oil. You will never achieve the desired results in this way. Your oil is badly contaminated with water. The way you are heating it is further accentuating the problem. You are heating it to 75- 85*C. What is happening is that the water in the oil is getting evaporated. Some of it gets collected at the top of the oil and some remains within oil in the form of bubbles. That is why you get improved BD value at 75*C. As soon as you bring down the temperature to 25*C, the entire vapour and bubbles gets condensed back into water thereby rendering the entire oil as it was rather worse than it was.

Follow the procedure as explainded by Sh. Bhattacharya or else transformer windings will also get badly affected besides rendering the entire oil useless.

BB Raina

as suggested by mr bhattacharya please do the filteration online albeit with a lesser capacity filter machine. thiswill remove moisture trapped inside the transformer housing and also sludge etc.