Developing reliable protection systems is critical for the advancement of medium-voltage direct-current (MVDC) grids. This paper highlights the significance of fault detection in MVDC grids, especially in ensuring the reliability and efficiency of renewable energy systems. This paper provides a comparative analysis of fault detection algorithms, including overcurrent, undervoltage, rate of change of current (ROCOC), rate of change of voltage (ROCOV), differential, and inductor voltage derivative methods. The performance of these algorithms is quantified by metrics such as the detection speed, accuracy, and sensitivity under diverse scenarios. The authors assess these algorithms within a multi-terminal MVDC grid designed for renewable hydrogen production, evaluating the detection speed across various fault types (bus and link faults) and conditions, including the variation in the fault location and resistance. The results reveal that the UV, ROCOC, ROCOV and LIVRD methods achieve detection speeds as high as 0.01 ms, outperforming other techniques under low-resistance fault conditions. By using uniform fault scenarios, we identify the most effective algorithms for rapid fault detection, aiming to enhance the protection strategies for MVDC grids. These findings underline critical performance differences between methods, guiding the design of tailored protection schemes that address specific fault challenges in renewable-powered grids. Additionally, the practical implications of these findings for designing resilient protection schemes in renewable-powered grids are discussed. Simulations are conducted using PSCAD/EMTDC V4.6 software, ensuring the consistency and accuracy of the performance comparison. The insights gained provide a concrete understanding of each algorithm’s trade-offs, enabling informed decisions when selecting optimal fault detection methods to ensure MVDC grid reliability.

The need of efficient electric transmission systems, the rise of renewable energy production, and the development of battery storage systems have driven the adoption of Modular Multilevel Converters (MMC), which offer better performance than conventional converters. However, the diagnosis of electrical faults in MMC is more challenging because more components are involved in the fault circuit. Particularly, ground faults (GF) are the most common type of faults in power systems, yet their diagnosis has not been extensively studied for AC-DC converters, where most industrial relays fail. This paper proposes a GF location method for MMCs based on the use of a high-value grounding resistor placed at the DC midpoint or AC neutral point. By measuring the voltage between its terminals and conducting frequency analysis, the fault position and fault resistance can be accurately located. The novelty of this method lies in its ability to locate the GFs on the AC side, DC side, or within a faulty submodule (SM) of the MMC. Numerous simulations were performed on a half-bridge three-phase MMC converter, yielding excellent results. Additionally, experimental tests were performed on a 60 kVA 12-level full-bridge three-phase MMC, validating the method.

The utilization of Direct Current (DC) railway systems is increasingly prevalent, as it constitutes the majority of urban tram power supply systems. Despite their high efficiency, the risk of ground faults is ever-present due to environmental issues and aging of the catenaries. These faults can interrupt the service for hours until repaired, requiring quick repair. To address this issue, this paper introduces a ground fault location method for catenaries in DC railway systems, based on the measurement of the DC voltage and ground current at each DC Traction Substation (TS). Then, the normalized ground currents relative to the overall fault current are compared with a model-based data pool, enabling the method to locate the fault along the protected catenary. The method's validity has been confirmed through numerous simulations and experimental tests. Initially, simulations were conducted on a three-TS DC railway model in Matlab-Simulink, yielding promising results. Subsequently, experimental laboratory tests were performed using uncontrolled rectifiers in the TS, also producing encouraging results. Finally, the suitability of the fault location method was verified using Hardware-In-the-Loop (HIL) tests emulating controlled rectifiers.

The increasing use of power electronic converters in DC systems introduces significant challenges for reliable ground fault detection, particularly in configurations that incorporate energy dissipation devices. Existing approaches often face limitations when faults occur within converter‐interfaced sections. This paper proposes a new method for ground‐fault detection, location, and severity estimation in DC networks equipped with DC/DC converters. The method analyses the voltage waveform of the grounding resistor that links the system neutral point—either the AC star‐point of the transformer or an artificial DC midpoint—to ground. By examining the characteristic response of this signal, the approach enables accurate detection of the fault, identification of the affected section (positive pole, negative pole, or DC chopper), and estimation of the fault severity through the calculation of the corresponding fault resistance. The proposed technique is first assessed through comprehensive simulation studies covering multiple fault scenarios. In addition, the method is experimentally validated on a laboratory test bench, demonstrating its effectiveness and robustness under different fault conditions and severities. Significantly, the experimental validation is carried out under real, non‐ideal operating conditions—where phenomena such as measurement noise and hardware imperfections are inherently present—further confirming the practical applicability of the proposed method.

Variable Speed Drives (VSDs) are key pieces in most of the industrial processes and thus, a secure operation must be ensured against possible harmful events such as ground faults. Fault location is a complex task that has been aggravated by the increasing presence of power converters. The switching commutations as long with the high frequency leakage currents can cause the malfunction of protection relays. This paper proposes a ground fault location method in the AC drive side of VSDs. The method is mainly based on a grounding resistor connected to the midpoint of the DC bus. Measuring the phase-to-neutral voltages of the AC drive side and the grounding resistor voltage, the method can determine the faulty phase. Moreover, it can estimate the fault position and fault resistance applying phasors equations with the fundamental and the switching frequencies. The method has been validated by means of computer simulations and experimental tests using a 140 kW power converter showing promising results for both fault position and fault severity estimations.