Auxiliary short-circuit fault classification for HVDC systems based on VCO

One of the great challenges of HVDC systems is the protection against short-circuit faults. The propagation of the fault effects in DC systems is faster than in AC networks mainly because to the low resistance, so a new breed of detection algorithms is required, much faster and more effective, with operation times to 10 milliseconds. This work proposes a step-forward scheme to detect and classify high and low resistance pole-to-pole and pole-to-ground short circuit faults in a MMC-HVDC system by combining the use of Voltage Controlled Oscillator (VCO) modules with a smoothing reactor. Case studies to verify the effectiveness of the proposed strategy are performed in PSCAD/EMTDC with a point-to-point HVDC system.