The reliability index SAIFI is divided into two parts: one
is due to the protection response and the other one is due to restoration. To
formulate them explicitly as a function of reliability parameters and binary
variables, an analytical simulation technique is used (Brown). In this
technique, the impact on the components of the system due to a contingency can
be calculated. This method assumes that faults are mutually exclusive. However,
one advantage of this technique is the ability to reflect small changes on
SAIFI due to small changes in the system.
In formulating the protection response component of SAIFI,
it is assumed that proper coordination of ASDs is always maintained. This
implies that the closest device to the fault will be actuated first. To
illustrate this technique, consider figure 1(a). In this figure, the node F1
represents the main substation. The node F2 represents the alternative feeder.
ASD1 is located between node k and j and its status is closed. For a permanent fault at node ,
ASD1 will open. Hence, the downstream costumers of ASD1 will experience a
sustained interruption. The effected customers are represented by .
At each node, the process is repeated.