Transformer LIFE
- Thread starter sdilucca
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bphgravity
Senior Member
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- Florida
Re: Transformer LIFE
My intuition tells me that at 25% overloading, the life expectancy would decrease by 25%. But I'm sure the two aren't directly proportional. I don't know of nor ever really heard of a life expectancy calculation, however this information may be available from the manufacturer.
My intuition tells me that at 25% overloading, the life expectancy would decrease by 25%. But I'm sure the two aren't directly proportional. I don't know of nor ever really heard of a life expectancy calculation, however this information may be available from the manufacturer.
- Location
- Lockport, IL
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- Retired Electrical Engineer
Re: Transformer LIFE
You are right, Bryan, that the relationship is not that of linear proportionality. It's an exponential, and the equation is complex. It includes a factor related to the physical properties of the materials used to construct the insulation system.
I have heard, as a general rule of thumb, that a 10 degree C rise in temperature, if held constant throughout the life of a component, will shorten the expected life of that component by half. But that does not tell us the answer to this question, since you would need to have a relationship between percent overloading and the amount by which the temperature of the windings would be elevated. If you make an effort to remove the extra heat generated by the overload, then the impact on the life of the transformer will be minimal.
You are right, Bryan, that the relationship is not that of linear proportionality. It's an exponential, and the equation is complex. It includes a factor related to the physical properties of the materials used to construct the insulation system.
I have heard, as a general rule of thumb, that a 10 degree C rise in temperature, if held constant throughout the life of a component, will shorten the expected life of that component by half. But that does not tell us the answer to this question, since you would need to have a relationship between percent overloading and the amount by which the temperature of the windings would be elevated. If you make an effort to remove the extra heat generated by the overload, then the impact on the life of the transformer will be minimal.
- Location
- Wisconsin
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- PE (Retired) - Power Systems
Re: Transformer LIFE
125% loading will result in windings losses of 156%. This increase in losses will generate more heat internal to the transformer (hot spot temperature) which will cause the insulation to age faster. A rough number is every 6-10C temp change will result in a doubling (or halfing) of the life of the insulation. I would not be suprised to find 125% loading result in a life expectancy of only 5%.
There was an ANSI standard C57.96 that was called "guide for laoding dry-type distribution and power transformers". Among other factors, the actual calculations will require knowledge of the transformer design temperatures.
125% loading will result in windings losses of 156%. This increase in losses will generate more heat internal to the transformer (hot spot temperature) which will cause the insulation to age faster. A rough number is every 6-10C temp change will result in a doubling (or halfing) of the life of the insulation. I would not be suprised to find 125% loading result in a life expectancy of only 5%.
There was an ANSI standard C57.96 that was called "guide for laoding dry-type distribution and power transformers". Among other factors, the actual calculations will require knowledge of the transformer design temperatures.
Re: Transformer LIFE
I suspect the power utilities do this calculation all the time. They don't seem to mind overloading transformers for a short time.
I would like to know what the expected life of a transformer is to start with. 10 years or 1000 years? The manufacturers' don't seem to be advertising the fact that someday their transformer will self-destruct. I also don't think they want to advertise the fact that you can get buy with using a 100KVA transformer to run a load that occasionally hits 125KVA.
I suspect the power utilities do this calculation all the time. They don't seem to mind overloading transformers for a short time.
I would like to know what the expected life of a transformer is to start with. 10 years or 1000 years? The manufacturers' don't seem to be advertising the fact that someday their transformer will self-destruct. I also don't think they want to advertise the fact that you can get buy with using a 100KVA transformer to run a load that occasionally hits 125KVA.
Re: Transformer LIFE
steve-
There are several Reason Utilitys allow their transformers to be overloaded
1. They don't operate at full load all day long. In this mode of operation transfomer life is greatly increased from the 7.42 year liftime.
2. In short durations the tempature rise of the windings are small therfore very little loss of life.
3. In the transmision system a transformer can cost Millions. My boss would laugh at me if I tried to change a transformer before it was near it end of life. He would rater get another 3 years out of the transformer before he has to change it.
A quick note about transformer life it is a point when the transformer's failure rate goes above a certain percentage. ( I have it at home but not at work) It doesn't mean it will fail it means that the transformer is more likely to fail.
steve-
There are several Reason Utilitys allow their transformers to be overloaded
1. They don't operate at full load all day long. In this mode of operation transfomer life is greatly increased from the 7.42 year liftime.
2. In short durations the tempature rise of the windings are small therfore very little loss of life.
3. In the transmision system a transformer can cost Millions. My boss would laugh at me if I tried to change a transformer before it was near it end of life. He would rater get another 3 years out of the transformer before he has to change it.
A quick note about transformer life it is a point when the transformer's failure rate goes above a certain percentage. ( I have it at home but not at work) It doesn't mean it will fail it means that the transformer is more likely to fail.
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