Fault-Line Identification of HVDC Transmission Lines by Frequency-Spectrum Correlation Based on Capacitive Coupling and Magnetic Field Sensing

The protection system of high-voltage direct-current (HVDC) system must detect, identify, and isolate the fault quickly to keep the system stable by only isolating the components that are under fault, while leaving the rest of the network in operation. However, the criteria of under-voltage and voltage-derivative protection systems may fail because there also arises a large voltage drop/variation on the healthy transmission line due to the electromagnetic coupling among HVDC transmission lines incurred by the sharp transient current in the faulty line. Thus, a fault-line identification technique of HVDC transmission lines by frequency-spectrum correlation was proposed in this paper, which is based on evaluating the similarity degree of frequency spectrum between the voltage of a line and the current of another. This technique was implemented and validated by simulation on a +/- 500 kV HVDC transmission system. The simulation model was integrated with a capacitive-coupling and magnetic-field-sensing-assisted platform comprised two paralleled induction bars, and an array of magnetic sensors to measure voltage and current. This identification technique can enhance the reliability of HVDC system by avoiding the unnecessary outages due to accidental shutdown of healthy lines, fostering the HVDC system development.