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Currently, we are developing an AC/DC conversion technology with the development of power semiconductors. Accordingly, DC is attracting attention because it is advantageous in the current transmission system. However, it has a problem that the cut-off technology required for DC system operation has not been secured yet. We are researching and developing a DC cut-off technology in several ways. We proposed a model that combines a superconducting fault current limiter and a DC circuit breaker. This is a configuration which a superconducting fault current limiter and a mechanical DC circuit breaker are connected in series. The superconducting fault current limiter limits the initial fault current and the mechanical DC circuit breaker cuts off the fault current. The mechanical DC circuit breaker consists of a high-speed DC switch, a LC divergent oscillation circuit and a surge arrester. This creates an artificial zero-point by affecting the blocking of the DC fault current according to the LC diverging oscillation circuit. In this paper, we analyzed the effect of the LC divergent oscillation circuit on the superconducting DC circuit breaker according to Reactor (L) and Capacitor (C). As a result, we analyzed the operating characteristics of the superconducting DC circuit breaker according to the application of the LC divergent oscillation circuit using the PSCAD/EMTDC program. Also, we confirmed the characteristics of the initial fault current limit rate of the superconducting fault current limiter and the possibility of controlling how the LC divergent oscillation circuit affects the DC arc generated at the opening of the mechanical DC contacts. more...

Currently, power semiconductors (IGBT, Thyristor, etc.) are used for the stability and high reliability of DC system operation. However, we have proposed a current limiting DC circuit breaker with superconducting winding to improve the stability of the DC system. This is superior in terms of fast cut-off speed and economy of power semiconductors, and is suitable for changes to the Point to Loads DC system that will be expanded in the future. A superconducting DC circuit breaker is a model in which a superconducting current limiter and a DC circuit breaker are combined. The superconducting fault current limiter uses a superconducting wire made of GdBCO material to limit the initial fault current to lower the current level of the fault current, and the DC circuit breaker blocks the reduced fault current from the superconducting fault current limiter by configuring a mechanical cutoff switch, passive elements L, C and SPD. In this paper, this superconducting DC circuit breaker model was designed and tested by giving two variables, and the operating characteristics were analyzed. The first is the superconducting wire connection method, and the second is the power supply voltage. In addition, the initial fault current, the time when the zero point of the fault current is generated, and the time when the shutdown is completed were compared and analyzed. As a result, it was confirmed that the helical type showed a higher current limiting rate than the spiral type, and the result of reaching a fast current zero point was confirmed. more...

We have studied the operation of the circuit breaker for 15 kV DC power grid with the combination of the breaker and the HTS Fault Current Limiter (FCL). The HTS FCL limits the fault current by introduce of the impedance under the fault condition, so the circuit breaker with the HTS FCL module can be expected to be able to break the higher prospective fault current successfully. As an attached module to the DC circuit breaker, we performed a design work for a DC resistive HTS FCL module with SuNAM's REBCO conductor with the stainless-steel stabilizer. Considering the operation delay time of the DC circuit breaker, the HTS FCL module should generate a proper impedance for 16 milliseconds at most without any damages. To verify the design results, we designed and make scaled-down model of the HTS FCL module. We also carried out the DC short-circuit test to check the feasibility and the fault current limiting characteristics of the suggested model. more...

The direct current (DC) grid range is rapidly expanding according to the increase of power generation capacity for the DC demands. In order to stably operate the DC grid system, we need a suitable DC circuit breaker for DC characteristics. We propose the superconducting arc-induction type DC circuit breaker. Lorentz’s force is occurred by the strong magnetic field is occurring by the superconducting magnet and the arc is occurring by the between Anode and Cathode. If we exactly control that, the efficiency of the arc-induction can be higher. In this paper, the electric field and according to the cut-off operation of the superconducting arc-induction type DC circuit breaker were analyzed. It is very important because the electric field and Lorentz force are an indicator for confirming the movement of the arc caused by the opening contacts. As a result, we confirmed that the Lorentz force calculated from the FEM showed a maximum increase ratio of 1101 times. more...

We research team has proposed a current-limiting superconducting DC circuit breaker that combines a High-temperature superconducting wire (HTS) with a DC circuit breaker, and secured its operation performance in our previous study via simulation. In this paper, we designed and produced an actual current-limiting superconducting DC circuit breaker, as well as analyzed its current limiting and breaking performance. In addition, the operation characteristics at different lengths of the HTS with increasing voltage were analyzed. The operation reliability of the proposed DC circuit breaker was demonstrated by a simulation system that was built similar to the actual system. more...

A wireless power transfer (WPT) method using superconductors was previously proposed (I. S. Jeong et. al. , 2013). Subsequently, the research team proposes superconducting WPT technology for electric vehicle (EV) application. The technology is designed to maximize efficiency by applying a superconductor to the transmission and reception resonant coils. The efficiency of wireless power transmission is determined by numerous variables, including the magnetic flux, the inductance of the resonant coil, and the mutual inductance. Therefore, it is possible to increase the efficiency by changing the shape of the resonant coil. In this paper, a spiral-type coil with a laminated structure was applied as a resonant coil for wireless power transmission for EV. This can increase the efficiency by generating a greater amount of magnetic flux than the single-layer spiral coil. In addition, a high coupling coefficient (K) and Q-factor can be obtained by applying a superconductor to the resonant coil. As a result, it is possible to implement wireless power transmission with higher efficiency than the conventional wireless power transmission methods. Simulation analysis was performed using High-Frequency Structure Simulation (HFSS), an electromagnetic field analysis program. more...

In this study, a new type of arc-induced DC (direct current) circuit breaker is proposed as a mechanical circuit breaker suitable for DC systems. It consists of mechanical contacts, induction needles, an induction ring, and a ground line. Powerful DC arcs are generated by the movement of the mechanical contact, but they are induced to the ground by the induction needles, and are exhausted. In this study, the cut-off characteristics of the arc-induced DC circuit breaker were analyzed using the Maxwell software. A simulation model was designed, and the electrical field distribution was analyzed according to the contact pole length. In addition, a prototype was fabricated based on the simulation results, and basic cut-off operation experiments were per-formed. As a result, it was possible to investigate the blocking characteristics of the arc-induced DC circuit breaker through the simulation and experiment. Moreover, it was confirmed that the induction needles can induce DC arcs. more...

The existing DC (direct current) circuit breakers used for LVDC (low-voltage direct current) extinguish the arc by using an arc chute. The arc chute has an insulating inner barrier and cuts off the current by increasing the length of the arc and raising the arc voltage. If the arc chute fails to extinguish the arc energy by dissipating heat, the arc generation time will increase, thereby raising the possibility of damage to the cut-off contacts. Therefore, we proposed a new arc-induction type DC circuit breaker with key components like mechanical contacts, an induction needle, and a magnet. The arc generated between the contacts is guided to the induction needle and then grounded via a ground wire before being extinguished. The induction needle is a critical component of such mechanism because it induces the arc. The performance of the DC circuit breaker is determined by modifying the induction needle. In this study, the operational characteristics of the arc-induction type DC circuit breaker according to the variation of the induction needle was analyzed using the Maxwell program. The shape and position of the induction needle were changed, and the changes in the electric field were compared via simulation. As a result, the electric field value was confirmed to have been improved by up to about 20.5% when the two variables were applied. more...

The DC circuit breaker we propose is a mechanical DC circuit breaker with superconducting fault current limiter. This is a method of applying a superconducting fault current limiter to shorten the cut-off speed of the mechanical DC circuit breaker. We confirmed the operating speed of the mechanical DC circuit breaker through experiments. In addition, simulation data were modeled through the PSCAD/EMTDC program. The operating characteristics were analyzed through the application of a superconducting fault current limiter. As a result, it was confirmed that the application of the superconducting fault current limiter increased the breaking capacity of the DC circuit breaker and made the operation speed faster. more...

In this paper, an inductor-type superconducting fault current limiter (I-SC FCL) in the dc power system is proposed to combine the benefits of an inductor and a superconductor. I-SC FCL minimizes the power burden on a superconductor and maximizes the cutoff performance. The inductor delays the rise of the fault current, and the superconductor limits the maximum value of the fault current. Then, they serve together to protect the circuit before the circuit breaker comes into play. The fault currents, limited by an inductor and a superconductor, are introduced into the mechanical dc circuit breaker (M-DCCB). M-DCCB could perform stably due to low power consumption. Analysis of the cutoff characteristics is carried out using the EMTDC/PSCAD program. As a result, the maximum value of the fault current is limited to approximately 2.6 times lower than the previously proposed M-DCCB. Additionally, a low power is burdened on I-SC FCL due to the delay part. more...

Recently, studies on the commercialization of magnetic resonance wireless power transfer (WPT) systems are underway domestically and internationally. The magnetic resonance WPT technology enables power transmission between transmitter and receiver coils with the same resonance frequency. If the resonance frequencies of the transmitter coil and receiver coil are different, the efficiency of the WPT will rapidly decrease. Various organizations, such as A4WP, have been striving to standardize resonance frequencies, but the countries around the world are sticking to their own distinctive standards based on the frequency bands available in their territories. Therefore, each country uses a slightly different resonance frequency band. In this paper, a frequency converter that enables WPT when the transmitter and receiver coils have different resonance frequencies is proposed. The frequency converter consists of two coils, and its structure is very simple. The two coils transmit power using the magnetic induction method, and frequency variation is possible using variable capacitors. It was confirmed from the experiment that WPT is possible even if the resonance frequencies of the transmitter and receiver coils are different. more...

Transformer-type superconducting fault current limiter (TSFCL) interruption system is a current breaking technology proposed by applying a transformer, superconductor, and mechanical dc circuit breaker. When the fault occurs, the fault current is limited due to the operation of the counter electromotive force by the transformer and the quenching of the superconductor. The fault current is then interrupted by the mechanical dc circuit breaker. In this paper, the transition and the interrupting behavior was analyzed according to the applied voltage to secure the stability and reliability of a TSFCL interruption system using the PSCAD EMTDC program. As a result, it was able to improve the current breaking time and the breaking capacity. Also, the burden imposed on a mechanical dc circuit breaker was reduced fivefold. more...

In this study, superconducting coil-type dc fault current limiter (SC-DC FCL) was proposed. The interruption and operation characteristics of the SC-DC FCL were analyzed, which was applied to a 7.98 kW-class photovoltaic (PV) generation system. Electro magnetic transients including direct current/power system computer aided design (EMTDC/PSCAD) have been used for the simulation. The simulation results showed that the interruption operation time of the mechanical circuit breaker, the power burden applied to the circuit breaker, and the peak value of the fault current were significantly reduced by the application of the SC-DC FCL. In addition, when the SC-DC FCL was applied, the fault current flowing through the line was limited by approximately 78% or more. more...

The wireless power transfer system using a magnetic resonance developed in 2007 was very useful and expectable. The use of the superconducting coil was suggested to improve the efficiency of the magnetic resonance system, and the increase in the quality factor was confirmed. The reflection coefficient of S -parameter $(S_{11})$ was analyzed under the mixed use of the superconducting coil and the normal conductor coil in this study, as the mixed use of both coils is inevitable in actual applications. As a result, the transmission efficiency was increased by the application of the superconducting coil due to the coil's high energy storage. more...