Abstract
This study presents calculation of fundamental frequency-based per phase digital impedance pilot relaying (DIPR) scheme for static synchronous compensator (STATCOM) compensated transmission line (TL) using two end synchronized measurement. DIPR involves computation of absolute value of ratio of estimated phasor sum of voltages to the phasor sum of currents of both ends. DIPR inherently differentiate between internal and external faults on the line. For all internal faults, computed value of DIPR ratio is equivalent to system and TL impedance value whereas for external faults, it is equal to line capacitance impedance value. This novel pilot relaying scheme is easy to set once the system parameters are estimated and has the ability to detect all types of faults and correctly classify faulty phase with mid-point connected STATCOM on TL. This scheme is immune to effect of STATCOM compensation mode, level of injection and its dynamic response. Also it is not affected by line charging capacitive current and fault transient resistance. The fault distance is estimated using the STATCOM current injection information for various types of fault with high accuracy, considering maximum fault resistance of 20 Ω. Accuracy and effectiveness of this scheme is evaluated in EMTDC/PSCAD simulation for 230 kV, 300 km, mid-point STATCOM compensated TL and in hardware setup with mid-point STATCOM on 100 V supply voltage having 200 km TL in offline mode. Results bring out the robustness, reliability and superiority of proposed novel pilot relaying scheme with fault location algorithm.