Novel pilot protection for voltage source converter high voltage direct current transmission lines by identifying model parameters

To solve the problems in the existing protection for high voltage source converter high voltage direct current (VSC-HVDC) transmission lines, such as insufficient sensitivity for main protection and slow operation for backup protection, a novel pilot protection for VSC-HVDC transmission lines by identifying model parameters is proposed. In the principle, the external fault is equivalent to a positive capacitance model, while the internal fault is equivalent to a negative capacitance model. For a ±60 kV VSC-HVDC simulation model of 300 km cable lines, the identified capacitance is positive line-to-ground one, about 80 μF, when an internal fault occurs; the identified capacitance is negative shunt one, about -1000 μF, when an external fault occurs. Internal faults and external faults can be distinguished by judging whether the identified capacitor is positive or negative. The results show that this principle, unaffected by transition resistance, line distributed capacitance and control type, can identify internal faults and external faults reliably within 10 ms under various operating conditions with sufficient sensitivity.