VOLTAGE CONTROL BY SVC
Ø The voltage-control action can be explained through a simplified block representation of the SVC and power system shown below. The power system is modeled as an equivalent voltage source Vs behind equivalent system impedance Xs as viewed from the SVC terminals.
Ø The system impedance Xs indeed corresponds to the short circuit MVA at the SVC bus and is obtained as
Xs = (Vb / Sc). MVAb in p.u.
Where, Sc = the 3 phase short circuit MVA at the SVC bus
Vb = the base line-line voltage
MVAb = base MVA
The SVC bus voltage is given by
Vs = VSVC + ISVC Xs
Ø The SVC current thus results in a voltage drop of ISVC Xs in phase with the system voltage Vs.
Ø The SVC bus voltage decreases with the inductive SVC current and increases with the capacitive current.
Ø The intersection of the SVC dynamic characteristic and the system load line provides the quiescent operating of the SVC as illustrated in the below figure.
Characteristics of the simplified power system and the SVC
Ø The voltage control action in the linear range is described as
Where ISVC is positive if inductive and ISVC is negative if capacitive.
Ø It is emphasized that the V-I characteristics described here relate SVC current or reactive power to the voltage on the high-voltage side of the coupling transformer.
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