Novel pilot protection scheme for transmission line with TCSC and TCR

Through fault analysis of Thyristor Controlled Series Capacitors (TCSC) compensated transmission line, a novel pilot protection scheme for transmission lines with TCSC and Thyristor Controlled Reactor (TCR) is presented. It is based on integrated impedance, which is defined as the ratio between the sum of voltage phasors and the sum of current phasors at two terminals of the transmission lines. The integrated impedance of the transmission lines is used to determine whether there is a fault inside the line or not. When an external fault occurs, the integrated impedance reflects the capacitance impedance of the protected line, its imaginary part is negative, and the absolute value of its imaginary part is large. When an internal fault occurs, the imaginary part of the integrated impedance on the fault phase is either a positive value or a small negative value. According to such characteristics, internal faults can be distinguished from external faults. The new scheme can be easily set and has the ability of fault phase selection, its behavior can hardly be influenced by capacitive currents, TCSC or TCR, and it can endure greater fault resistance. Digital simulations based on 750 kV transmission systems show that the presented scheme has high sensitivity and reliability.