Grounded HVDC grid line fault protection using rate of change of voltage and hybrid DC breakers
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Different HVDC grid types and the respective protection options are discussed. An earthed bi-pole HVDC grid was modeled in PSCAD, and using simulation results, the necessity of di/dt limiting inductors to contain the rise of fault currents within the capacity of current hybrid DC breakers is demonstrated. The impact of different inductor sizes on current rise was studied. A fault detection and localization scheme using the rate of change of voltage (ROCOV) measured at the line side of the di/dt limiting inductors is proposed. The protection system was modeled and tested under different fault types and locations. The results show that the proposed method of HVDC grid protection is feasible using the current hybrid DC breaker technology. A systematic procedure for setting the necessary protection threshold values is also demonstrated.