Due to limited amplitude and controlled phase of current supplied by inverter-interfaced renewable power plants (IIRPPs), the IIRPP-side distance protection of lines connected to IIRPPs fails to detect the fault location accurately, so it may malfunction. The composite sequence network of a line connected to an IIRPP during asymmetrical faults is analyzed, and an adaptive distance protection based on the analytical model of additional impedance is proposed in this study. Based on open circuit property of negative-sequence network at the IIRPP-side, the equivalent impedance of power grid and current flowing through fault point are calculated in real-time using local measurements, which are substituted into the analytical model of additional impedance to calculate fault location. In the case of negative-sequence reactive current injection from IIRPPs during asymmetrical faults, the error of calculating fault point current from local measurements is analyzed and corrected to ensure reliability of the proposed protection. The proposed protection alleviates the effect of fault resistance in a system with weak sources. In addition, the proposed protection can adapt to different grid codes (GCs), the operation mode change of the power grid, and the capacity change of the IIRPP. PSCAD/EMTDC test results verify the effectiveness of the proposed protection.

Due to the influence of inverter control, the short-circuit current provided by distributed photovoltaics (PVs) exhibits new characteristics, such as a controlled amplitude and phase angle, resulting in the malfunction of the current protection and differential protection of distribution networks with high PV penetration. In this paper, the equivalent high-frequency impedance model (EHFIM) of PV power generation and the analysis method of a fault high-frequency superimposed network are proposed. On this basis, we analyze the fault high-frequency superimposed network of a distribution network with high PV penetration and propose a high-frequency fault analysis-based pilot protection scheme, in which the range of frequency employed for protection (FEP) is analyzed theoretically. By comparing the relationship between the high-frequency operating impedance and the high-frequency restraining impedance, the internal and external faults are identified. The proposed protection scheme has the advantages of a fast trip, low requirement for data synchronization, immunity to inverter control and the PV operation mode, and adaptability to lines with teed feeders. The experimental results show that the proposed protection scheme can accurately identify internal and external three-phase, two-phase, and two-phase grounding faults and is resistant to both fault resistance and noise interference.

Based on the inherent characteristic of the carrier‐based pulse‐width modulation converters, the response of the first carrier frequency harmonic (FCFH) current in the voltage source converter (VSC)‐based high‐voltage direct current (HVDC) transmission system is analysed under different fault conditions in this paper. A new protection scheme for the VSC‐based HVDC transmission systems is proposed based on the FCFH currents. By extracting the harmonic currents at both the endings of the DC transmission cable, the fault type can be identified. The VSC‐based HVDC test system is modelled in the PSCAD/EMTDC and the proposed protection scheme is evaluated with a variety of values of the fault resistance and the fault locations. Comprehensive test studies show that the performance of the proposed protection scheme is inspiring. It can recognise the internal and the external faults correctly.

When single-phase-to-ground (SPG) or phase-to-phase (PP) faults occur on collection lines of an offshore wind farm with modular multilevel converter-based high voltage direct current (MMC-HVDC) transmission, the fault current level may be low or even approach zero due to the controlled current at both ends of the collection line. As a result, the traditional current differential protection may malfunction. To address this issue, a method is proposed that utilizes open circuit characteristics of the negative-sequence network to indirectly calculate the fault point negative-sequence voltage by the negative-sequence voltage at the protection installation location. The fault distance can then be determined. The introduction of a twiddle factor eliminates the influence of fault resistance, improving the accuracy of fault distance calculation. Based on this calculated fault distance, a high-sensitivity differential protection scheme is proposed. This proposed protection can maintain sufficient sensitivity and trip correctly during collection line SPG and PP faults. It solves the issue of traditional current differential protection malfunctioning in low-fault current scenarios of transmission lines with inverter-based resources (IBRs) on both ends. In addition, it can adapt to different reactive power support strategies and operation modes of offshore wind farms. Test results indicate the effectiveness of the proposed protection.

With the rapid development of renewable energy, multi-terminal flexible DC grids composed of modular multilevel converters have been widely used in power systems. To ensure the safe and stable operation of a DC grid, this paper proposes a DC line protection scheme for MMC-based DC grids using AC/DC transient information. In the proposed scheme, the difference between the transient voltage root mean square ratios (DTVR) on both sides of the current-limiting inductor of DC lines is used to identify the DC line fault, and the instantaneous zero sequence voltage (IZSV) of the AC side of the converter station is used to discriminate the faulted poles. According to the theoretical analysis result, a fault criterion setting method suitable for faulted pole discrimination is proposed. The proposed scheme is based on local information and tested in a PSCAD/EMTDC model of a four-terminal MMC-based DC grid. The simulation results show that the scheme can fast and accurately identify faults.