However, the contribution of non-ICT failures to the probability
of operator errors (events I7 and I8) is difficult to estimate
as it depends on the GUI design and on the operators’
performance. Therefore, determining P(I7) and P(I8) requires
the input from electrical utilities on what can result in operators
errors based on their operational experiences. Once these
2976 IEEE TRANSACTIONS ON POWER SYSTEMS, VOL. 28, NO. 3, AUGUST 2013
probabilities are obtained, the probability of the top event can
be evaluated using (1)–(3). Next, the most critical sources of SA
errors can be identified and design improvements can be made
to enhance operators SA.
Even though this analysis provides a lower bound of the probability
of operator errors as it focuses on themodeling of a single
electrical substation, it can be used as the basis of the required
extended model for estimating the frequency of operator errors
with an adequate degree of accuracy.