The calculation of the continuous allowable current of an underground cable is determined by various characteristics. To calculate the allowable current in cables with alternating magnetic fields such as AC, special phenomena such as the proximity effect and skin effect must be applied. However, there are no standards or research related to the calculation of the continuous allowable current of a DC power cable that does not have an alternating magnetic field. In this paper, a quantitative DC cable continuous allowable current calculation formula of direct burial laying was derived by applying the existing AC cable continuous allowable current calculation method to the DC system. We developed a calculation tool that can calculate the continuous allowable current of DC cables using the derived formula. Assuming the cable conditions (cable specification, laying conditions, soil characteristics, arrangement, and number of strands, etc.), a continuous allowable current simulation of DC cables was performed. In addition, the level of contribution to the continuous allowable current value was analyzed by classifying the parameter categories into major and minor factors in the order of influence on the allowable current among the determined calculated parameters. As a result, the effectiveness of the DC cable continuous allowable current calculation tool derived by performing the allowable current calculation simulation was evaluated, and the allowable current calculation method of the HVDC cable was established.

The Hybrid Modular Multilevel Converter (HMMC) topology—comprising full-bridge (FB) and half-bridge (HB) submodules—is effective for DC fault clearance in HVDC systems. However, to prevent overvoltage in lower-arm full-bridge submodules (FBSMs) during valve-side single-phase-to-ground (SPG) fault mitigation—an uncommon yet critical internal fault in bipolar HVDC systems—the proportion of FBSMs used must account for approximately 86.6% of the arm voltage, compared to 43.3% for DC-side fault blocking. This diminishes the economic advantage of HMMC over fully full-bridge MMC topology. This paper proposes an HMMC SPG fault mitigation method using thyristor-based current commutation branches on the lower arms and a ground-side mechanical interrupter, while maintaining the minimum number of FBSMs required for conventional DC fault clearance. The method mitigates SPG-resultant lower-arm overvoltage by commutating current into the thyristor branches, after which the mechanical interrupter clear lower arms current, and subsequently thyristor branches are turned-off to clear the SPG-valve side fault. Additionally, the pole current is cleared using a mechanical breaker or passive oscillation DC circuit breaker (CB), effectively suppressing upper-arm submodule (SM) overvoltage under SPG valve-side fault in both short- and long-distance HMMC bipolar links. Although additional equipment is required, it incurs no on-state losses during steady-state operation. The proposed method is compared with existing SPG fault clearance approaches for HMMC bipolar systems. Its effectiveness is validated through PSCAD/EMTDC simulations and benchmarked against prior SPG fault clearance methods for HMMC systems.

With the growing demand for scalable and resilient high‐voltage direct current infrastructure driven by offshore renewables and international power exchange, multi‐terminal DC (MTDC) systems are emerging as a key solution. However, their deployment is hindered by the lack of effective DC fault protection. Conventional single‐layer architectures assign detection, limitation, and interruption to a single breaker, resulting in over‐engineered designs and high system complexity. This study proposes a multi‐layer protection approach that decouples fault current management into two dedicated functions: a thyristor‐based fault current limiter for initial current suppression and an active resonance circuit breaker for selective fault isolation. A comparative simulation using the CIGRE B4.57 MTDC benchmark in PSCAD/EMTDC evaluates the proposed scheme against a widely adopted hybrid DC circuit breaker baseline. The results demonstrate reduced peak fault current, lower surge‐arrester stress, and a significant decrease in semiconductor requirements. Together, these outcomes confirm that the proposed multi‐layer architecture provides comparable interruption performance while offering practical implementation advantages and improved scalability for future MTDC systems.

With the increasing deployment of DC power systems, particularly in DC distribution systems, there is a growing demand for rapid and effective fault current limiting solutions. Conventional fault current limiters (FCLs) often suffer from limitations in terms of response time, size, and operational complexity. As a solution to these challenges, this paper proposes a hybrid FCL based on a pyro conductor switch (PCS), which combines passive limiting elements with an active switching mechanism. The proposed PCS FCL consists of a pyro fuse, an IGBT switch, a limiting inductor, and a damping resistor. Upon fault detection, the IGBT switch is first turned off to initiate current transfer into the limiting branch. Subsequently, the pyro fuse operates by explosively severing the embedded conductor using a pyrotechnic charge, thereby providing galvanic isolation and reinforcing current commutation into a high-impedance path. This operational characteristic enables effective fault current suppression without requiring complex control or real-time sensing. A detailed analysis using PSCAD/EMTDC simulations was conducted to evaluate the current limiting characteristics under fault conditions, and a prototype was subsequently developed to validate its performance. The simulation results were verified through experimental testing, indicating the limiter’s ability to reduce peak fault current. Furthermore, the results demonstrated that the degree of current limitation can be effectively designed through the selection of appropriate current limiting parameters. This demonstrates that the proposed PCS-based FCL provides a practical and scalable solution for improving protection in DC power distribution systems.