• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 1998.06a
• /
• pp.207-210
• /
• 1998

Surface electrical conduction in insulator is most important factor to assess the insulation performances of outdoor insulating materials. In this paper, contamination performance of the widely used materials for outdoor insulator - porcelain, EPDM, Silicone rubber - were discussed by measuring properties of average leakage current and scintillation discharge pulses under artificial contamination conditions. The artificial contaminations used were deionized distilled water fog, 0.5wt% NaCl salt fog of light pollution and 2wt% NaCl salt fog of medium pollution. The average leakage current was appeared linearly with applied voltage at dry and clean surface condition. The magnitude of leakage current was almost same at different kinds of samples. In case of deionized distilled water fog, the characteristics of leakage current and applied voltage was most different to that in case of dry and clean condition. In case of salt fog pollution condition. The leakage current was increased above critical voltage. The scintillation discharges were also activated at the level the leakage current and scintillation discharges were increased with increasing pollution degree. The resistance to pollution properties of silicone rubber appeared excellent among them.

• Steel and Composite Structures
• /
• v.28 no.2
• /
• pp.195-207
• /
• 2018

First-order reliability method (FORM) is enhanced based on the search direction using relaxed conjugate reliability (RCR) approach for the embedded nanocomposite beam under buckling failure mode. The RCR method is formulated using discrete conjugate map with a limited scalar factor. A dynamical relaxed factor is proposed to control instability of proposed RCR, which is adjusted using sufficient descent condition. The characteristic of equivalent materials for nanocomposite beam are obtained by micro-electro-mechanical model. The probabilistic model of nanocomposite beam is simulated using the sinusoidal shear deformation theory (SSDT). The beam is subjected to external applied voltage in thickness direction and the surrounding elastic medium is modeled by Pasternak foundation. The governing equations are derived in terms of energy method and Hamilton's principal. Using exact solution, the implicit buckling limit state function of nanocomposite beam is proposed, which is involved various random variables including thickness of beam, length of beam, spring constant of foundation, shear constant of foundation, applied voltage, and volume fraction of ZnO nanoparticles in polymer. The robustness, accuracy and efficiency of proposed RCR method are evaluated for this engineering structural reliability problem. The results demonstrate that proposed RCR method is more accurate and robust than the excising reliability methods-based FORM. The volume fraction of ZnO nanoparticles and the applied voltage are the sensitive variables on the reliable levels of the nanocomposite beams.

• Journal of Electrical Engineering and Technology
• /
• v.7 no.6
• /
• pp.876-883
• /
• 2012

The paper investigates three types of transfer function methods for detecting displacements of winding in a model transformer. To acquire these transfer functions, the measuring method of input voltage, current and its response is used in impulse method. The applied impulse voltages had three rising times, which were short rising time (less than 0.6 ${\mu}s$), medium rising time (about 0.8 ${\mu}s$) and long rising time (about 1 ${\mu}s$) in front waves. Every 10 measurements of voltage and current waves were averaged from 50 measurements of voltage and current waves. These transfer functions were tested in normal, 24mm elevated and 48mm elevated windings conditions and were analyzed with correlation coefficients and spectrum deviations. In the analysis, the results depend on the types of transfer functions and the rising times of input voltages.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.28 no.6
• /
• pp.52-59
• /
• 2014

This paper deals with the effect of decomposition products which occur in breakdown of mineral oil, on the insulation characteristics of its oil. Breakdown tests in the oil were conducted by the proposed experimental methods under a quasi-uniform field and AC HV (60Hz). The breakdown voltage in the oil shows characteristics of dispersion from successive breakdowns and, it is found that there are three patterns of the decomposition products behavior at the process of breakdown progress in the oil. Finally, the breakdown voltage dispersion in the oil can be described in detail based on the behavior patterns of the decomposition products and its diffusion time.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
• /
• 2006.05a
• /
• pp.264-267
• /
• 2006

This paper describes the accident analysis by modeling the current transformer mounting in meaium voltage metal-clad switchgear(MCSG). In analyzing the accident the reconstruction at the current transformer mounting(VCB connecting guide) has to be taken into account. The accident was modelled as a 3-phase ground fault mounting between the end plate of a high voltage lines and the safety shutter at the current transformer mounting of the VCB inside the metal clad switchgear. Since the outside maintenance of the metal clad switchgear is restricted by the enclosed compartments, its circumference has to be kept clean. Through the reconstruction results, it was confirmed that the fault of the enclosed switchboard could be reduced when the shutter made of Fe material was changed into an insulation.

• Proceedings of the KIPE Conference
• /
• 2014.07a
• /
• pp.333-334
• /
• 2014

Converters employing IGCTs usually require di/dt snubber and Over Voltage Protection (OVP) circuit for the protection of IGCTs and fast diodes. In these IGCT-based converters, conventional di/dt snubber and OVP circuit dissipates a significant amount of power loss. To reduce this loss of conventional di/dt snubber and OVP circuit, this paper proposes a flyback type snubber circuit with di/dt limiting characteristic for IGCT-based converters in medium voltage wind turbines. This flyback type snubber circuit simply consists of a flyback type transformer and diode. The proposed circuit reduces loss and simplifies conventional di/dt snubber by adopting the flyback type transformer. Loss analysis of conventional di/dt snubber and OVP circuit is performed for the 3-level NPC type back-to-back VSC supplied from grid voltage of 6.9kV. The proposed flyback type snubber circuit can save the loss of conventional snubber circuit in the 3L-NPC type back-to-back VSC in multi-MW MV wind turbine. The proposed snubber circuit has a fewer number of components and improved efficiency leading to a reliable and efficient wind turbine systems.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.60 no.8
• /
• pp.1560-1565
• /
• 2011

The environmental pollution caused by green-house gases such as $CO_2$ and $SF_6$ has been becoming the main issue of industrial society. Many developed countries are making efforts to minimize the amount of $CO_2$ emission come from the operation of high voltage electrical apparatuses. As a part of these efforts, 180 countries signed the Kyoto Protocol in 1997 to cut back on their green-house gas emissions. Nowadays, the study on the development of dry air insulated switchgear (DAIS) which is known as an eco-friendly electrical apparatus is in progress. A DAIS is advantageous for minimizing the effect of impurities and enhancing the dielectric characteristics over an air insulated switchgear (AIS) by applying constant pressure to an enclosed cubicle. Therefore, a study on the electrical insulation performance of dry air as a gaseous insulation medium is conducted in this paper to substitute a gas insulated switchgear (GIS) for DAIS. As results, it is verified that the AC dielectric characteristics of dry air are similar to those of air and the lightning impulse dielectric characteristics of dry air are superior to those of air at 1bar pressure condition. However, dry air is of inferior dielectric characteristics to $SF_6$ at 4bar pressure condition. Finally, it is suggested that the internal pressure of DAIS should be over 4bar pressure to develop a high voltage switchgear which has similar electrical performance to a conventional GIS. Also, the empirical formulae on calculating the maximum electric field intensity at sparkover of dry air are deduced by experiments according to pressures. It is expected that these results are helpful to design and develop a high voltage electrical apparatus.

• Journal of Korean Society on Water Environment
• /
• v.28 no.6
• /
• pp.917-922
• /
• 2012

In order to improve applicability of a microbial fuel cell the laboratory-scaled study has been performed by adopting an air-cathode MFC system with high concentrated anaerobic slugies in this study. The concentrations of microbes are grouped into three types, Type A (TS 1.7%), Type B (TS 1.1%) and Type C (TS 0.51%). The open circuit voltage $(V_{oc})$ characteristics showed that the medium microbes concentration of 1.10% (Type B) kept a constant voltage of 1.0 V for 150 hours, which showed the longest time among three types (Type A and Type C). The discharge charge curves for a closed circuit with $500 \Omega$ also showed that Type B generated a stable discharge voltage of 0.8 V for a longer time as in the open circuit voltage case. This could be explained by the relatively large amount of the attached microbes. Under the $V_{oc}$condition the COD removal efficiency of Type B was found to be low for a long time, but those of Type A and C were found to be high for a short period of time. Therefore, the suspended microbes could decrease the coulombic efficiency. It was concluded that the high $V_{oc}$ was caused by low COD and the $V_{oc}$ became low after the COD removal. The COD reduction resulted in an unstable and low working voltage. From the polarization characteristics Type A was found to show the highest power density of $193\;mW/m^2$ with a fill factor of 0.127 due to the relatively high remaining COD even after the MFC reaction.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.16 no.6
• /
• pp.610-617
• /
• 2011

This paper proposes a novel and direct dead-time compensation method of the 3-phase inverter using space vector pulse width modulation(SVPWM) topology. The proposed dead-time compensation method directly compensates the dead-time to the turn-on time of the effective voltage vector according to the current direction of the medium voltage reference. Each phase voltages are determined by the switching times of the effective voltage vectors, and the practical switching times have loss according to the current direction by the dead-time effect in the 3-phase inverter. The proposed method adds the dead-time to the switching time of the effective voltage vector according to the current direction, so it does not require complex d-q transform and controller to compensate the voltage error. The proposed dead-time compensation scheme is verified by the computer simulation and experiments of 3-phase R-L load.

• Proceedings of the KIEE Conference
• /
• 2009.07a
• /
• pp.2089_2090
• /
• 2009

본 논문은 한전에서 사용되는 25.8kV 가스 절연 부하개폐기(이하 개폐기)에 대해 장기과통전시험, 부하전류 개폐 및 접점마모시험, 가스 기밀재 가속열화시험을 통해 신뢰성을 평가하였다. 국내 개폐기의 신뢰성 및 수명에 대한 척도를 평가한 결과, 모든 시료가 $B_{10}$ 수명 20년 이상을 보증할 수 있는 것으로 나타났다.