Search

For stability in the direct current (DC) power grid, it is very important to limit the current of the fault section and to protect the system in the fault condition. That is the core technology of the DC power grid. This paper suggests characteristics and a limited range of the fault current for the new model as the significant protecting technology in the DC power grid. Such new model is the arc-induction-type DC circuit breaker (CB) combined with a magnet. The magnetic arc-induction-type direct-current circuit breaker (DCCB) consists of a neodymium magnet, an induction needle, and electrical contacts. During fault operation, the arc occurring between the contacts is induced to the induction needle. To increase the induction effect, Lorentz force is applied to blow the arc. A magnet was applied to reduce the initial fault current and to induce magnetic flux. The simulation data were analyzed using the Maxwell 3D software program. The electric field included the electric force and the electric charge. Therefore, it could analyze the arc as the electric field. The simulation was performed based on the preceding study on induction needle. As a result of the simulation, it was confirmed that the electric field value of the induction needle increased when the DCCB was combined with a magnet. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The global consumption of electricity is on the rise due to the industrial and population growth. The number of power generation and distribution facilities is increasing in order to meet the growing demand. Furthermore, the low impedance of power systems is causing a fault current that exceeds the capacity of the existing circuit breaker. In this paper, a method was suggested which limits the initial fault current by combining a superconducting fault current limiter (SFCL) with the existing flux-offset-type fault current limiter (FCL). Results showed that the initial fault current within a half cycle was limited by approximately 60%, while the fault current after a half cycle was limited by approximately 80 %. Overall, 99.8% of the fault current was limited, while the power burden on the SFCL was reduced by more than 50%. [ABSTRACT FROM AUTHOR]

The wireless power transfer (WPT) characteristics between the transmitter and receiver coils according to the existence of ferrite were analyzed in this study to improve the transmission distance of superconductor resonance coils. To set the optimal reflection coefficient, the thickness increased by 1 mm, from 0 to 10 mm. It was found that the transfer efficiency improved with the lowest reflection coefficient at the thickness of 2 mm. The 2-mm-thick ferrite was applied to the transmitter coil, and the reflection coefficient was measured by the distance. As a result, the transfer efficiency with ferrite was highest at the distance of 2500 mm. Also, it was confirmed that the WPT characteristics were improved up to 500 mm by the application of ferrite. It is believed when the superconductive WPT system is organized using such advantageous ferrite, its transmission distance and efficiency improvement can be secured. [ABSTRACT FROM AUTHOR]

In wireless power transmission (WPT), the magnetic induction method has recently led the commercialization of wireless power chargers for mobile devices, wireless electric toothbrushes, etc. So, studies have been continuously followed in various fields. However, WPT systems needed improvements in transmission distance and efficiency to expand the application range. To solve this problem, a magnetic resonance method has been introduced. Magnetic resonance has improved the transmission distance and efficiency of WPT. In this paper, a superconductor was applied to a transmission coil to enhance its WPT efficiency using magnetic resonance. The existing normal conductor coils could be optimized by changing the coil sizes and winding methods, but the improvement of the efficiency of WPT was limited. The superconductor coil had the characteristics of 0 resistance at the critical temperature. Moreover, as the volume of the current density increased more than 100 compared with the existing copper coils, the maximum resonance characteristics could be induced when the impedances matched. The results confirmed that the WPT of the superconducting coil using magnetic resonance was more efficient than that of the conventional copper coils. [ABSTRACT FROM AUTHOR]

In this paper, a flux offset-type fault current limiter was proposed as a new means of reducing fault currents. The flux offset-type fault current limiter is a device that is integrated into the fault current technology, to which the flux offset principle of a transformer is applied, and is combined with a transformer and a fast switch. To secure the operation reliability of a flux offset-type fault current limiter, a simulation system was constructed to analyze its operation characteristics by generating a single line-to-ground fault and a triple line-to-line fault. According to the test results, the system performed stably without any impedance, because the primary and secondary winding fluxes of the transformer offset each other at normal times. However, when a fault current event occurred, because the fast switch was activated to limit the fault current by opening the secondary windings of the transfer within an average of 9.5 ms, which is shorter than the operation time of the existing electric circuit breakers by 3-5 cycles, the system is likely to perform protective coordination with circuit breakers in the future. In addition, the application of this current limiter could keep the fault current limit ratio to about 96 %. [ABSTRACT FROM AUTHOR]

In this study, a new concept is proposed on a combination device with functions of a commercial transformer and a superconducting fault current limiter (SFCL). This device serves as a transformer by stepping the voltage up or down in normal condition. When a transient phenomenon occurs in the power system, it serves as an SFCL to limit the fault current. The device quickly detects the line current using a current transformer (CT), and is based on the high-speed, silicon-controlled rectifier (SCR) interrupter operation. This is done by identifying the fault using an SCR switching control system. The test results showed that the fault current was limited by the impedance of the superconducting element a half cycle after a fault occurred. An SCR that initially had a normally open contact was turned on within a half cycle. However, an SCR with a normally close contact was turned off after a half cycle because the current dropped below the holding current after a half cycle. The voltage of the superconducting element was low in the step-down turn ratio condition of the transformer. This was because the secondary and tertiary windings were connected in series due to the SCR-1 turn-off condition, and the sum of voltages on each winding appeared on the superconducting element. By combining the existing power device technology and an SFCL technology, it is expected that the existing problems of an SFCL can be addressed to construct a smart power system. [ABSTRACT FROM AUTHOR]