Pilot protection method for bipolar CSC‐HVDC transmission lines based on transient currents behaviour

Abstract

The unnecessary prolonged operating time of conventional current differential protection under high-impedance DC line faults is an important issue affecting the continuity of power supply. This issue originates from the extreme differential current fluctuation under fault conditions. This paper presents a reinforced pilot protection algorithm for bipolar CSC-HVDC transmission lines to achieve a selective and sensitive performance without sacrificing the protection speed. In this regard, the characteristics of low-frequency transient modal currents are investigated along with the impact of discharging capacitive current under various fault conditions. Based on the features arising from line-mode compensated currents, it is shown that their opposite changing directions induces a positive high-value differential current during DC line faults, whereas the compensated line-mode currents follow the same changing trend under external faults. After detecting internal faults, the faulted pole is detected by utilizing the polarity of ground-mode components. Compared to other pilot protections, the proposed protection provides more reliability, selectivity, and sensitivity with high operating speed. Moreover, it has robust performance against discharging capacitive current, asynchronous measurement, line parameters uncertainty, and noise. Various simulation tests are performed on a ±500 kV HVDC test system in PSCAD to verify effectiveness of the proposed protection.