When a fault occurs on a section or a component in a given power system， if some or all protective relays（PRs） and circuit breakers（CBs） associated do not work properly， or in other words， a malfunction or malfunctions are happening with these PRs and/or CBs， the outage range could be significantly extended. As a result， the complexity of fault diagnosis could be increased. The existing analytic models for power system fault diagnosis do not systematically address the possible malfunctions of PRs and CBs， and hence may lead to incorrect diagnosis results if such malfunctions do occur. Given this background， based on the existing analytic models， an effort is made to develop a new analytic model to well take into account of the possible malfunctions of PRs and CBs， and further to improve the accuracy of fault diagnosis results. The developed model could not only estimate the faulted section（s）， but also identify the malfunctioned PRs and CBs as well as the missing and/or false alarms. A software system is developed for practical applications， and realistic fault scenarios from an actual power system are served for demonstrating the correctness of the presented model and the efficiency of the developed software system.