M.R Aghamohammadi - Iran Dynamic Research Center Power & Water University of Technology (PWUT) Tehran-Iran
S Hashemi - Iran Dynamic Research Center Power & Water University of Technology (PWUT) Tehran-Iran
M.T Barforooshi - Mazandaran Regional Electric Company Mazandaran-Iran

Load shedding is generally considered as a precautionary measure when voltage collapse is anticipated and can potentially result in blackout conditions. This countermeasure is used as the ultimate strategy to stop the blackout propagation into the rest of the network. In this paper, a new approach for load shedding against voltage collapse based on evaluation of voltage security margin is presented. In this approach, a new load shedding index namely load-to-source impedance ratio (ZL/XTh) is proposed for recognizing the most critical load buses from short term voltage instability point of view. A relatively large value of ZL/XTh index indicates an improved system voltage security. In order to improve the power system’s voltage security margin, the most effective buses with the least value of ZL/XTh index are chosen for implementing load shedding. The proposed approach has been implemented in Iran’s North Transmission Network with promising results demonstrating its effectiveness and applicability.

Voltage Security Margin, Load Shedding, ZL/XTh index