Improved Integrated Impedance Scheme for Series Compensated Transmission Line

The paper presents an improved protection scheme for series compensated transmission line. The proposed relaying scheme is based on integrated impedance which is defined as the ratio of the sum of voltage phasors to the current phasors from two ends of a transmission line. The literature shows that the integrated impedance based protection scheme serves as a better option than the conventional current differential protection. However, line-charging current causes significant error in integrated impedance method as well as in conventional current differential method. This paper presents improved integrated impedance-based protection scheme which compensates line charging current using equivalent π-model of the transmission line. The proposed improved integrated impedance scheme is developed in phase domain. The proposed scheme is compared with the integrated impedance and conventional current differential methods. Simulations are carried out in an Alternate Transient Program (ATP) on a 750 kV transmission line equipped with Thyristor Controlled Series Capacitor (TCSC). Simulation results show the superiority of proposed scheme over existing schemes.