Improvement of Voltage stability and Critical Clearing Time for Multi-machine Power Systems Using Static VAR Compensator

Abstract
The present paper studies the effect of equipping static VAR compensator, SVC in multi-machine power system to improve the voltage stability and critical clearing time CCT. of multimachine power system. Three static VAR compensators, SVCs are connected with certain power system buses to stabilize the system voltage and improve the overall power system stability subjected to different disturbances for a wide range of operating conditions . Also, the SVCs improve the power system critical clearing time to a significant values in case of unrepeated three phase short circuit fault at all system buses for different operating conditions. The results indicate the importance of installing SVCs to grid power system due to their effect not only on stabilizing the system voltages but also increasing the power system critical clearing time. The critical clearing time is obtained by increasing the fault time interval until the system loses its stability. Increasing the CCT can help in the reliability of the protection system and reduce the protection system rating and its cost. The studied 3-machine nine- bus power system is modeled and simulated using MATLAB software package. 

Keywords: Multi-machine power system - Voltage stability improvement – Static VAR Compensator - Critical clearing time.

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