Secure Phase Comparison Schemes for Transmission-Line Protection Using Synchrophasors

The segregated phase comparison technique is a notable form of differential protection which compares the phase angle of end currents of a transmission line. The literature shows that phase differential protection serves as a better option for transmission-line protection due to its simplicity, sensitivity, selectivity and comprehensibility. However, line-charging current causes a significant error in the phase angle of two end currents of a transmission line. This paper presents improved phase comparison whichP compensates error due to line-charging current and a function of a cosine scheme using the equivalent- π model of the transmission line. The phase differential function is developed using phase coordinates. The scheme is compared with the existing scheme like, conventional scheme based on line currents, the positive-sequence component of line currents and a mixed combination of line currents. The global positioning system is used for time-synchronised measurements and fiber optics are considered for data communication. Simulations are carried out in an Alternate Transients Program/Electromagnetic Transients Program on an IEEE 14-bus system, and a protection scheme is implemented on one of the tie lines. The results demonstrate the accuracy of the proposed approach over the existing schemes.