Uncertainty Analysis of Fault-Tree Models for Power System Protection

Abstract

ABSTRACT. This paper presents an algorithm that computes the uncertainty in the availability of power system protection using fault-tree modeling. The probability of a fault-tree top event such as "Protection Fails to Clear the Fault" is evaluated in terms of the nominal value and uncertainty of each of the basic-event probabilities. The proposed algorithm starts by obtaining the fault-tree top-event expression in the switching domain (Boolean-domain) and then converting it to an availability expression in the probability domain. The algorithm then utilizes the multiaffine nature of this reliability expression in the exact assessment of its uncertainty. An example of a typical power system protection scheme is presented wherein exact numerical estimates are obtained for both the nominal value and variance of the top-event probability.