Coordinated control of the power compensation equipments located in local substations of the district unit power system

Decreasing stability of power system by voltage instability makes that all power system face with serious problems of stability. That is attributable to the difficulty of controlling the power system. So it is necessary to keep the voltage of load bus in range of the limited level to supply high quality of electric power. Therefore we describe and suggest on this paper that a plan for coordination control between UPFC(Unified Power Flow Controller), Shunt elements(Shunt capacitor & Shunt reactor) and ULTC(Under Load Tap Changer) among compensators and also describe the method to keep or control the voltage of power system in allowable ranges.