Abstract: Interconnections of the modern bulk electric power systems,while contributing to the operating economy and reliability,result in an increased complexity of fault diagnosis.In this paper,a complete analytic model of fault diagnosis was presented by analyzing principles of protective relay setting and circuit breaker trip,and an effective solving method for the proposed model was developed.In the complete analytic model,the fault hypothesis-the actual states of the suspected fault equipment,as well as the malfunction of protective relays and circuit breakers,was treated as logic variables,and the principles of protective relay setting and the rules of the circuit breaker trip were completely expressed with a set of logic equations.Each solution of the complete model represents a mode of fault information（the faulty states of the equipment,operations of protective relays and circuit breakers）,which can completely describe the fault scenarios.The operation rules of protective relays and circuit breakers were fully analyzed and the coupling relations between the fault equipment and operation of protective relays/circuit breakers are intactly reserved in the complete analytic model,removing the defects of the previous analytic models.Several examples had showed that the complete analytic model with the intact coupling relations can improve the accuracy and error-tolerant ability of the current fault diagnosis methods.