Life of oil-immersed insulation structures

SINCE THERMAL DETERIORATION, commonly called aging, is recognized generally as the predominant factor in determining life expectancy of oil-immersed insulation structures, its effect on samples of various materials has been the subject of extensive research.^{1, 2} In using these experimental data to determine the effect of loading on apparatus life, it is convenient to define the “aging factor” at a given temperature as the ratio of the corresponding rate of deterioration to the rate at some reference temperature, as in Figure 1. For a varying temperature cycle, the integral of a plot of the corresponding aging factors, as in Figure 2, gives the “equivalent aging time,” or the time required, at the reference temperature, to produce the same aging. The cumulative effect of several cycles may be obtained by adding the equivalent aging times at a common reference temperature.