The probability of events I4-I6 can be estimated if the probabilities
of the ICT failures at the substation are available. These
can be obtained directly from the component manufacturers or
from field or test data. Fig. 19 shows the fault tree of the events
leading to missing information from the process level (I4),
which can occur in case of failure of any of the IEDs or MUs.
It can be seen that AND gates are used to illustrate redundancy,