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.