A Novel Method of Combined DC and Harmonic Overcurrent Protection for Rectifier Converters of Monopolar HVDC Systems

This paper presents a novel protection method for monopolar high-voltage direct current (HVDC) converters. This method uses the secondary and tertiary currents of the converter transformers and based on dc and harmonic contents of the currents decides for the security of the converter. The new protection method detects the location of the fault inside the converter and based on that issues a signal for single-phase disconnection in the ac system to eliminate the fault. It will be shown that the new method is not only faster compared to the conventional protection methods but also can be easily applied to the existing HVDC systems without imposing any significant requirement. The Hydro-Quebec HVDC test system is used to present the simulation results and to ensure the validity and functionality of the proposed protection method.