SUMMARYThe paper presents a new approach to assessment of the power system security. Using fuzzy membership functions of power system elements, it continuously quantifies the security state of a power system, as opposed to conventional methods which use off-line screening for the most vulnerable system states. It introduces global fuzzy security index (GFSI) of the power system using system's variables characterized by fuzzy sets of a trapezoidal form. GFSI is calculated by multiplying the security membership grade (SMG) values of the power system's segments that exhibit the lowest SMG values. The power system security levels are traced continually through time using real data of power flow and state estimation calculations as well as measurements of variables inaccessible by the load flow analysis. The GFSI enables the system operator to identify the insecure state and then continuously monitor the distance of the power system's actual state and the insecure one. Application of the algorithm is illustrated using the data of Bosnian power system.
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