Realistic insights into impedance seen by distance relays of a SSSC-compensated transmission line incorporating shunt capacitance of line

Abstract

• When in the fault path, reactive power compensation by SSSC reduces reactance seen. • When outside the fault path, reactive power compensation increases reactance seen. • Real power compensation, particularly at midpoint, leads to reduced reactance seen. • A very high underreaching probability arises from SSSC in conventional relays. • Neglect of shunt capacitance causes a significant probability of relay underreach. In practice, the series compensation is applied to medium-/long-length transmission lines. Such lines include significant shunt capacitance, neglecting of which is expected to noticeably influence the impedance seen by distance relays. Taking the shunt capacitance of a transmission line compensated by the static synchronous series compensator (SSSC) as well as other affecting factors into account, this paper derives precise mathematical expressions governing the apparent impedance seen by the distance relay of the line. Through the acquired expressions, the research conducts sensitivity studies considering different compensation scenarios and locations for the SSSC. The studies make an attempt to produce realistic insights into ideal tripping characteristics of the distance protection of the under studied line, and also into the susceptibility of the impedance seen to output parameters of the SSSC. In addition, the research’s findings well demonstrate the extent to which neglecting the shunt capacitance of the line would contribute to mis-operation of the distance relay.