How often the transformer oil should be treated ? 2

[edison123]

One of my clients filters the oil of all his running transformers every year religiously. Is it necessary ?

I advised him to do DGA / BDV instead every year to assess the condition of the oil (e.g. moisture content > 30 ppm) instead of filtering/treating the oil by rote. What do the trafo experts think ?

 

[edison123]

Other than the water content, can any of the dissolved gases be used as an indicator for the requirement of oil filtering ?

 

[mgtrp]

Acidity and interfacial tension (IFT) are good indicators of oil condition. If inhibited oil is used, you could also monitor the amount of inhibitor left and filter/replace inhibitor once it is low.

Annual filtering is probably more than what is required.

 

[ScottyUK]

See what the DGA results say. Yearly DGA is a fairly common frequency unless there are known problems or it is a critical system transformer. Yearly filtering is unusually frequent: in my opinion if such regular filtering is necessary due to oil condition then the transformer is in real trouble, otherwise it is a waste of time and money.


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If we learn from our mistakes I'm getting a great education!

 

[edison123]

Thanks mgtrp and Scotty.

Is there any standard that specifies a standard frequency of oil filtering ?

Which standard specifies the test parameters for dielectric strength test (Break-Down Voltage - BDV test) ?

I am looking for like gap settings, rate of voltage rise, acceptable breakdown voltage etc.

 

[prc]

edison, filtering will only improve water content and BDV and not other parameters.Hence filteration is required only in case there is excessive water content (by saturation percentage)and poor BDV.There is no standard calling for annual filteration.

You can refer to following standards on oil maintenance
1)IEC 60442 of 2005-10 2) IEEE C57.106-2006 3)IEEE C 57.140-2006 Guide for evaluation and reconditioning of liquid filled transformers.

 

[edison123]

Thanks prc being as helpful as always. I was kinda hoping you would pitch in.

In case of high but stable DGA values, how to remove those damn gases ? From our earlier conversation on DGA values, I kinda thought oil filteration would remove the DG's along with water. Am I wrong ?

 

[mgtrp]

There is a book, Guide to Transformer Maintenance (or something similar) published by the SD Myers company that is an excellent reference on transformer oil testing and maintenance if you are after general information (from memory, it includes all the info that you are looking for).

If you are looking for a standard to wave in front of you client, IEEE C57.106 (Guide for Acceptance and Maintenance of Insulating Oil in Equipment) may be of some use. Actual procedures for carrying out the tests are as per various ASTM standards, ASTM 1816 for dielectric breakdown strength.

I'm afraid my copies of the above are 11,000 km away at the moment, so I can't provide any specifics.

 

[edison123]

Thanks mgtrp. Now, I will hunt down that IEC standard and that Meyers book.

I am asking these questions for personal edification. Then I can do all the waving & weaving in front of my clients .

 

[mgtrp]

A vacuum filter can be used to remove gases.

 

[prc]

edison,filtering will remove all dissolved gases,provided machine has a vaccum chamber.Meyers book is running on third edition( you can get it from their site digital or hard copy)But authoritative and latest information is in those standards mentioned by me.If you are in IEC world refer to IEC ,otherwise ANSI/IEEE std.On all aspects of oil and its testing there is a small handbook by Nynas.com,you can get it from their site.