Transformer life

[linkstrap]

Can anyone tell me where i can find a chart which shows trnasformer life vs temperature over 40degree ambient?

 

[jbartos]

Suggestion: Visit

http://www.hsb.com/thelocomotive/Story/FullStory/ST-FS-TRANAGE.html

For time-aging reliability models, the instantaneous failure rate can be represented by the exponential equation[3] that follows:

f(t) = a exp(b t)

[3] P.A.Tobias & D. Tindale, "Applied Reliability," Van Norstrand Reinhold Co., New York, NY, 1986

 

[cuky2000]

Check the following references:

a- IEEE Std. C57.91-1995, "Guide for Loading Mineral-Oil-Immersed Transformers,
b- IEEE Std. C57.96-1989 “ Guide for Loading Dry Type Distribution and Power Transformers”
c- IEC Standard 354, "Loading Guide for Oil-Immersed Power Transformers."

There are software in the market such as EPRI's Power Transformer Loading program (PTLOAD 6.0) that calculates transformer temperatures, thermal ratings, insulation loss-of-life, and gas bubble formation based on user-specified physical parameters for the transformer and user-specified load and air temperature data.

In general the loss of life could be estimated using the Arrhenius life expectancy
theory based on the following relation


Log[E(t)] = A + B/T_abs

T_abs = T_hs +273.

Where:
E = Life expended in during time interval t
T_hs = Temp hot spot (oC) = Ambient Temp + Hottest- spot winding temp.
t = Time in hours
T_abs = Absolute temp (oK)
A, B = Constant for life expectancy curve

See the following additional references:

thread250-28296

http://www.usbr.gov/power/data/fist/fist1~5/1~5_fg14.htm

http://www.usbr.gov/power/data/fist/fist1~5/1~5_fg15.htm

 

[linkstrap]

Thanks a million

 

[RajT]

As a rule of thumb based on continued operation, every deg over 40dge( as in your case) will reduce the life by 1 year

 

[Bung]

Another rule of thumb I have come across is every 10deg C rise will halve the life.

I would suggest this really only applies to any organic components, eg paper insulation, oil etc. Temp rises low enough to avoid accelerated failure (through burning or oxidation) are not likely to severely affect any inorganic materialsas much (copper, ceramics etc).

Bung
Life is non-linear...

 

[SooryaShrestha]

Bung has rightly said "Temp rises low enough to avoid accelerated failure (through burning or oxidation) are not likely to severely affect any inorganic materialsas much (copper, ceramics etc)." To add a few more to it:
Becuse of the temperature rise the insulation deteriorates. However if by some means the deterioration is resisted, then the life will not deteriorate as previously thought. When oils are changed it was considered life enhancement. But what has happened is in fact the oxidising inhibitor has reduced. So if the oil is regenerated inside the transformer till the color is changed to LIGHT YELLOW and not to the level of clear colorless, then the inhibiting natural chemicals remain in the oil as intact, which will prolong the life of oil thereby the transformer. Some researchers of ABB consider to filter to the extent of colorless by adding inhibitor in order to enhance the life.
Yes it is true that with the rise of temperature the life is reduced, provided the temperature is well above 90 degree celsius. Otherwise, I think the life does not decrease, that is if the transformer temperature is maintained at 50 degree celsius above 40 degree celsius ambient and regularly checking its acidity and IFT.