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As the utilization of DC systems increases worldwide, the importance of DC cutoff technology is increasing. We proposed a hybrid DC cutoff technology combining an SFCL (superconducting fault-current-limiter) and a mechanical DC circuit breaker. This model can perform a fault-current-limiting operation through the quenching of the SFCL and a breaking operation through an artificial cutoff zero point of a mechanical DC circuit breaker. In particular, the SFCL is responsible for the growth of the initial fault current according to the DC characteristics. As the DC system's supply and demand increase, the DC system's capacity also increases. Therefore, the fault-current-limiting capability of the SFCL should be increased according to the increasing DC system breaking capacity. The fault-current-limiting capability can be increased by increasing the superconducting wires used in the SFCL. Current commercially available SFCLs use bifilar-helical-type and bifilar-spiral-type winding methods. These have the disadvantage of increased volume with increased capacity. To compensate for these disadvantages, we proposed a bifilar-meander-type winding method. In this paper, a new bifilar-meander-type winding method was introduced. In addition, the structural and electromagnetic parts of the existing winding method and the bifilar-meander-type winding method were compared and analyzed for differences. The program used for this analysis is the electromagnetic analysis Maxwell program. As a result, it was confirmed that the bifilar-meander-type winding method is superior to the conventional bifilar-helical and bifilar-spiral types. [ABSTRACT FROM AUTHOR]

We proposed a superconducting DC circuit breaker that can reliably cut off the fault currents in preparation for the DC system. It consists of a superconducting element and a mechanical DC circuit breaker. The mechanical DC circuit breaker is connected in parallel with a mechanical high-speed switch, an LC divergence oscillation circuit, and a surge arrester. This provides stable cutoff operation due to the fault-current-limiting operation of the superconducting element and the artificial current zero point of the mechanical DC circuit breaker. In this paper, the operating principle of the LC divergence oscillation circuit that creates an artificial current zero point was reviewed based on the theory. We used experimental data to model the time constant of the initial fault current, the arc model generated by the mechanical high-speed switch, and the experimental equipment. As a result, the LC divergence oscillation circuit was confirmed in the simulation, and simulation modeling was reviewed based on the theoretical principle of generation. [ABSTRACT FROM AUTHOR]

DC systems are modernly starting to come into the spotlight again due to the carbon-neutral policy, the development of semiconductor devices for power, and the increase in digital loads. We need to prepare in advance solutions to problems that may arise from fault currents due to transients for future DC power grid models. In the case of DC, there is no current zero-point because there is no frequency. Therefore, a large switching surge is generated when the circuit breaker cuts off the fault current. The possibility of insulation breakdown is greater than that of AC in severe cases. We consider power semiconductors or superconducting current limiters as an alternative. However, DC breaking cannot be safely achieved by itself. For reliable DC breaking, mechanical circuit breakers must be used with them. Among the mechanical shut-off methods, we adopted the divergence oscillation method. It has the biggest advantage compared to other methods in that it has a simple structure by composing passive elements and can artificially create zero current. In addition, it can be applied to a power semiconductor and a superconducting current limiter to perform a high-reliability cut-off operation. In this paper, we conducted simulation analysis by configuring the DC power grid and DC cut-off system through the PSCAD/EMTDC program. Results confirmed that the application of the LC divergence oscillation circuit can reduce the cut-off time and reduce the power burden of the mechanical DC circuit breaker (MCB). [ABSTRACT FROM AUTHOR]