Estimating reliability of an electrical insulating system

Estimates of capacitor reliability may be obtained from 100 percent high potential testing, and from lot sampling tests to destruction, as well as performance in service. High potential test yields were compared to reliability estimates obtained on extrapolated cumulative distribution functions based on destructive breakdown tests performed on lot samples. Products from three different periods of manufacturing yielded similar results. It was found that the extreme value probability distribution function provides a better fit to observed data from lot sampling destructive testing than the distributions based on the normal probability or noncentral t-distributions. It was also found that reliability estimates based on 100 percent high potential testing are in close agreement with those estimates based on lot sampling tests to destruction, provided the correct probability distribution is applied.