Effects of the Quality Factor of reactor on the TCSC characteristics and the Dual Impedance Solution Phenomenon

This paper investigates how the reactor´s quality factor (labeled as Q at power frequency) affects the characteristics of TCSC and what principle should be followed in designing an experimental TCSC setup. Since no close-form representation of the fundamental frequency impedance (EFFI) against the firing angle can be obtained considering the quality factor of the reactor, detailed electromagnetic transient simulation is employed for the investigation. Results show that, under the same firing condition, the EFFI of TCSC using reactor with low Q value may present considerable resistance component compared with that of the ideal case when Q is infinite. Moreover, it is found that the EFFI of the TCSC using a reactor with limited Q can be either inductive or capacitive for a specified firing angle when it is fired in a line current reference mode. This so-called dual impedance solution phenomenon is analyzed in detail in the paper.