A High Speed Single-Ended Fault-Detection Method for DC Distribution Line—Part II: Protection Scheme

As the second part of two series paper, the protection scheme is proposed. First of all theoretical analysis and threshold calculation methods are introduced. Aiming to the problem that relay needs to send alert signal instead of trip signal in non-effectively grounded system when single pole to ground fault occurs, a fault type identification method is introduced based on the ratio of absolute values of two poles voltage derivatives. Then 1 mode voltage based protection scheme is developed and the feasibility of design of criterion based on pole voltages, impact of sampling frequency, fault types, resistance and branch on the proposed criterion are discussed comprehensively. MMC based two-terminal and radial and VSC based four-terminal dc distribution systems are simulated in PSCAD. Relay behaviors are tested in three systems under different locations, resistances and types of faults. Results show that the proposed methods can be applied to both MMC and VSC based dc distribution systems and are immune to the fault type, fault location and fault resistance.