Fault component integrated impedance-based pilot protection scheme for the TCSC compensated EHV/UHV transmission line

This paper presents a new pilot protection scheme based on fault component integrated impedance (FCII) of transmission line with thyristor controlled series capacitor (TCSC) and controllable shunt reactor (CSR) through the fault analysis of transmission line with TCSC and CSR. The FCII is defined as the ratio of the sum of the fault component voltage phasors across the two terminals in the transmission line to the sum of the fault component current phasors through the same line. It can be used to identify if there is a fault on the line or not. If the fault is out of the line, the FCII reflects the line capacitive impedance that has greater amplitude; if the fault is on the line, it reflects the system and line impedance that has relatively smaller amplitude. We can distinguish between internal faults and external faults according to the calculated value of amplitude of FCII. The new pilot protection can be easily set and is not sensitive to compensation level and dynamics of TCSC and CSR after being applied in the TCSC compensated transmission lines. The FCII based protection has the ability of fault phase selection. It is hardly under the influence of capacitive current and immune to higher fault transition resistance. The effectiveness of the new scheme is validated by simulations with ATP and Northwest China 750 kV project data.