There are many excellent analytical methods available for evaluating t
he average reliability indices of industrial substation configurations
based on various models and the average failure and restoration/repai
r rates of the components that are interconnected to form an operating
substation configuration. Many models are based on the assumption of
independence of component failures and restoration activities. This pa
per presents actual utility supply operational characteristics to reve
al the possible significant differences between theoretical and actual
reliability indices when component failures and restoration activitie
s are not independent. This paper also presents a customized simulatio
n model for assessing the reliability indices of an industrial substat
ion configuration as a function of calendar time based on the historic
al utility supply data and an industrial substation's operational conf
igurations, loading patterns and restoration activities dependent on t
he severity of the power interruption. The simulation model will be di
scussed in some detail and is applied to a radial industrial substatio
n configuration. The historical reliability performance of the utility
-industrial customer is discussed in some detail regarding the theoret
ical expectations and changing utility and industrial facility operati
onal characteristics. The proposed simulation model provides a means o
f accurately assessing the reliability of an industrial site's electri
cal supply without recourse to detailed and lengthy analytical calcula
tions that can be erroneous when an industrial site's operational acti
vities are time dependent and a utility delivery system performance is
quite variable.