The design of reliable industrial and commercial power systems is of considerable interest to
many people. Prior to 1962, a qualitative viewpoint was taken when attempting to achieve
this objective. The need for a quantitative approach was first recognized in the early 1960s
when a small group of pioneers led by W. H. Dickinson organized an extensive AIEE survey
of the reliability of electrical equipment in industrial plants. The AIEE survey that was taken
in 1962 was followed by several IEEE reliability surveys, which were published in 1973
through 1979. These surveys from the the 1970s were the basis for the reliability data contained
in IEEE Std 493-1980. Six additional IEEE reliability surveys have been conducted
and published during the 1980s and have been updated in this revision of IEEE Std 493-1997.
The 1990 edition included pertinent tutorial reliability material and the cost of power interruptions
IEEE Std 493-1997 presents two new chapters, Chapter 9, a new methodology for estimating
the frequency of voltage sags at industrial and commercial sites, and Chapter 10, a methodology
for estimating the number of tests required to demonstrate reliability of emergency and
standby systems. New appendixes have been added on high- and low-voltage circuit breaker
reliability data, guarantees of gas turbines and combined cycle generating units, transmission
line and equipment outage data, interruption costs, and expectations for service reliability.
The existing appendices have been updated.