SCADA based under frequency load shedding integrated with rate of frequency decline

Speed and accuracy of under frequency load shedding (UFLS) has a vital role in its effectiveness for preserving system stability. In any case load-shedding still remains the ultimate resource for emergency condition. Initial rate of change of frequency is a fast and potentially useful signal to detect the overload when a disturbance happens. In order to improve the under-frequency load shedding performance, in this paper, a global load shedding scheme integrated with rate of frequency decline as an extra variable is proposed. The new SCADA based scheme is devised to overcome the shortcomings of previous adaptive UFLS procedures, and to provide a fast and yet reliable method to maintain system integrity. The paper first investigates the impact of relevant generator and system parameters on frequency behavior of generators following a disturbance. The proposed frequency load shedding scheme is then presented and simulated on a 39 bus test system