Enhanced transmission line pilot impedance and pilot protection

This study proposes a novel pilot protection for transmission lines by using enhanced transmission line pilot impedance (ETLPI). The ETLPI is defined by the ratio of the voltage difference of fault-superimposed component to the current summation of fault-superimposed component at both terminals of the protected line and used to distinguish the internal faults from the external faults. For the external fault, the amplitude of ETLPI is greater than the positive-sequence impedance of the protected line, whereas it is smaller than the positive-sequence impedance for the internal faults. The pilot protection scheme based on the ETLPI has the feature of avoiding the influence of line distributed capacitance and the saturation of current transformer (CT) as well as the transient response of coupling capacitor voltage transformers (CCVT). Therefore the pilot protection is suitable for different length transmission lines. Both theoretical analysis and test results obtained from EMTP digital simulation and the physical simulation have demonstrated that the pilot protection is of high reliability and good adaptability.