This paper introducesa new expert system (ES) for faulted section determination in electrical power system andinterpretingthe performance of the protective system (relays and circuit breakers). The introducedESrequiresinformation about the power system configuration and about the contacts status (open/closed) of the circuit breakers and protective relays. It can determine the faulted section quickly and accurately for all types of faults including simultaneous faults. It is general, i.e.it can be usedwith any power system,due to the separation between the Facts and Rules. The introducedES isdeveloped and tested by CLIPS environment (C Language Integrated Production System) which uses forward chaining to derive conclusion. The performance of the introduced ES is tested for several power systems, IEEE–6 bustest system, IEEE–9 bustest system andIEEE–14 bustest system, and it shows a distinct performance for all tested systems. But for space limitation, we present in this paper the performance results of the introduced ES for the IEEE–9 bustest system only.