Sangseob Song

Study on Maximum Operating Condition of Resistive Type SFCL Using YBCO Coated Conductor

The most important thing in developing a superconducting fault current limiter (SFCL) is to find the maximum operating condition for each current-limiting element to increase its SFCL capacity. The maximum operating condition can be defined using Vmax, Tr, Imax and Iq, which are detected after the quenching of the SFCL. In this study, YBCO coated conductor whose characteristics were proved as the superconducting fault current limiting element was used to test the operating characteristics of the unit current limiting element and to find the maximum operating condition using Vmax, Tr, Imax and Iq, which are detected after the quenching against the fault current according to the fault angle. YBCO coated conductors used in the test are one wire with stainless-steel stabilizing layer and one wire with no stabilizing layer. Critical current value is 70 Arms and the critical temperature is 90 K. The YBCO coated conductor with non stabilizing layer had a critical current of 80 Arms and a critical temperature of 90 K. Therefore, the two YBCO coated conductors in this study had different critical currents and an identical critical current of 90 K.

Defocus blur estimation using a Cellular Neural Network

Blur identification is one of the most important parts of digital image processing. A conventional blur that occurs in images is out of focus, which is generated because of lens defocus. In this sense, many researchers have presented methods to estimate defocus blur so far. This paper shows how the Cellular Neural Network (CNN) can be used to estimate defocus blur parameter. After the point spread function (PSF) parameter is obtained by the CNN, defocused blur images can be restored effectively.

Effect of the Resistance of Two Different Coated Conductor on the Current-Limiting Performance of Flux-Lock Type Superconducting Fault Current Limiters

The recent increase in power demand has been pressuring industries to continuously extend or expand power sources and transmission and transformer systems. On the other hand, the equivalent impedance of power systems is decreasing. Accordingly, the fault current magnitude in power systems is increasing. Because of such developments, and the rising need to counter this trend, current-limiting technology has been getting much attention as it can efficiently limit the short-circuit faults and improve power system reliability. For this purpose, studies are being carried out on the superconducting fault current limiter (SFCL). In particular, studies on SFCL where normal-conducting devices are combined, instead of the resistor-type SFCL that depends only on the superconductor, are being continued. The development of the element that is suitable for the superconducting fault current limiter combined with the normal-conducting device is also underway. In this study, YBCO thin-film wires that have and do not have a stainless steel stabilizer layer, which is recently studied as the superconducting current-limiting element, were used as superconducting elements of the flux-lock and transformer-shape SFCL consisting of normal-conducting core and coil. The effect of the difference between the resistance values of the two elements on the current-limiting performance of the flux-lock and trans former-shape current limiter was evaluated. For this purpose, the resistance values trend of the two superconducting elements was examined. The initial operational characteristics were compared in terms of quenching time (Iini, IImi, and Tr) and stability (Vmax).

Tensor decomposition of Toeplitz Jacket matrices for big data processing

In this paper, we consider the tensor decomposition (TD) of Toeplitz Jacket (TJ) matrices for big data processing by using the conventional higher order singular value decomposition (HOSVD) algorithm and Tensor train (TT) decomposition. In order to use HOSVD algorithm and TT decomposition, we reshape the given matrix and make it as a tensor. Due to the property of Toeplitz matrices, we use a truncated TJ matrix in stead of given matrix to reduce the complexity of TD. The results verified that the TD of the truncated TJ matrices gains a lower complexity due to smaller size of factor matrices and core tensors.

Design of long time interleaver for future S-DMB services

In this paper, we present an efficient interleaver, designed for future personal mobile satellite services. Burst errors incurred by long term fading of mobile satellite channels will seriously degrade the service quality. Interleaving is an effective solution to this situation, by randomizing the errors before the channel decoders. This paper describes the design and the simulation results of a convolutional interleaver for personal mobile satellite system based on orthogonal frequency division multiplexing (OFDM) transmissions, especially IEEE mobile WiMax specification. We first analyze long term fading characteristics of mobile satellite channels, and analyze the simulation results of bit error rate (BER) performance according to various system parameters and channel conditions.

Evaluation on Current Limiting Properties During 3-Phase Connection Between the Wires for SFCL and HTS Cable

Advantages of YBCO thin film type wires are as follows. First, their high critical current density allows effective handling of normal and fault currents. Second, high index values can lead to fast fault current limiting because of the rapid build-up of resistance. Third, a variety of stabilizing materials can be employed in YBCO thin film type wire, resulting in more flexible adjustment of limiting resistance after the quench. In this study, the wires for the current limiter and cable were selected through an over-current conducting (transport) test that took into account the characteristics of the YBCO thin film type wire. The current limiting characteristics of the wires for the current limiter and cable according to the fault type and fault angle were examined. The tests were conducted in three phases, and the fault type and fault angle were examined for single-line-to-ground fault, double-line-to-ground fault and triple-line-to-ground fault at the fault point of R-phase 0 that was defined as the fault standard in the test. The YBCO thin film type wire for the current limiter with a critical current of 80 Arms, critical temperature of 90 K and voltage rating of 0.6 Vrms/cm had stainless steel stabilization layer, while the Bi-2223Ag wire for HTS cable with a critical current of 110 Arms, critical temperature of 106 K and voltage rating of 2.5 Vrms/cm had silver stabilization layer. The required lengths were determined considering the voltage rating of wires, and the wires were respectively wound on a straight former and a spiral former.