We investigated deep levels in n-type 4H-SiC epitaxy layer of the Schottky barrier diodes (SBD) and Junction Barrier Schottky (JBS) diodes by using deep level transient spectroscopy (DLTS). The I-V characteristics of the JBS devices show ~100 times lower leakage current level than SBDs owing to the grid structures in JBS. The reliable responses of the diodes for deep level transient analysis showed from C-V characteristics. Several deep electron traps were revealed by DLTS measurements in epitaxial layers in 4H-SiC. In both types of diodes, the peaks corresponding to shallow energy levels were observed with slightly different values of 0.132 eV for JBS and 0.186 eV for SBDs. The two remarkable deep level peaks (J2 and J3) have been obtained with 0.257 eV and 0.273 eV in JBS, and they were analyzed to have a similar trap concentration of ~10¹⁴ cm^-3. The comparison results showed that the defects could be related with device fabrication procedures such as ion-implantation and growth.

Transient earth voltage (TEV) signals propagate on metal surfaces when partial discharge (PD) occurs due to the deterioration of insulation performance in the operation of gas-insulated switchgears (GIS). A TEV sensor has advantages of high sensitivity and convenient installation for detecting PD defects. However, the TEV sensor depends on imports in domestic and detailed studies have not been conducted. In this study, a sensor was designed and fabricated by the TEV principle and its response characteristics were evaluated for detecting PD defects, which were simulated as protrusion on conductor (POC), protrusion on enclosure (POE), and free moving particle (FMP) defects. Finally, the PD-induced TEV signals were measured and phase-resolved partial discharge (PRPD) patterns were analyzed to identify the type of defect.

In this paper, the flux-lock type superconducting fault current limiter (SFCL) using double quench was suggested and its transient current limiting characteristics were analyzed. The suggested flux-lock type SFCL using double quench consists of two magnetically coupled windings and two high-T_C superconducting (HTSC) elements connected in series with each winding. To analyze the transient current limiting characteristics of the flux-lock type SFCL using double quench, the short-circuit tests according to the fault angles, which affect the transient component of the fault current right after the fault occurs, were executed. From the comparative analysis for the short-circuit tests at both 0° and 90° fault angles, the useful transient current limiting operations of the suggested flux-lock type SFCL through the double or the single quench occurrence were confirmed.

The basic performance of the ground system is evaluated as the ground resistance by applying low frequency current below 1 kHz. However, characteristics of the ground system should be analyzed by high frequency current up to 1 MHz since transient currents having a few hundred kHz component flow during a line-to-ground fault and/or a lightning strike. This paper deals with the design and fabrication of a wideband ground impedance meter (WGIM) which measures the impedance of ground systems in ranges from 65 Hz to 1.28 MHz. Also, a noise elimination algorithm using a digital bandpass filter is proposed. The maximum error of the WGIM is 4.91% in the measurement frequency range.