• Journal of the Korean Institute of Telematics and Electronics A
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• v.33A no.2
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• pp.114-121
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• 1996

Thin film Ba$^{0.7}Sr^{0.3}TiO^{3}$ (BST) capacitors were fabricated on SiO$_{2}$/Si substrates by RF magnetron sputtering method and characterized at microwave frequencies ranging from 40 MHz to 1GHz to examine the dielectric dispersion of the capacitors. The BST thin films were electrode material of BST thin films capacitor which is known as one of the best electrode materials for BST films. 50$\AA$-thick titanium (Ti) layers were introduced to increase adhesion between bottom Pt and SiO$_{2}$. The leakage current density of the capacitors was about 1.7${\times}10^{7}A/cm^{2}$ at 1.5V and the dielectric constant was about 140 at 1MHz. Microwave measurement patterns having a coplanar waveguide type were fabricated and their S parameters were measured using network analyzer. After de-embedding parasitic components in microwave measurement patterns nearly frequency-invariant dielectric constant of about 120 was extracted in the measurement range of 40 MHz to 1 GHz.

• Proceedings of the KSR Conference
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• 2007.05a
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• pp.1694-1700
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• 2007

In the electrified section, both of return current and signal current are flowing in the same rail in common. But signal current shall be allowed to flow in the specific track circuit and not in the other circuit while the traction return current shall come back to power sub-station. This paper presents measuring system that use both sensor and antenna. The aim of the system is to achieve the difference in current between the two rails and the presence of trimming capacitors. In order to improve the transmission level, trimming capacitors are connected between the two rails at constant spacing. To maintain the balance of traction return current, rails of both sides may be jointed by the so-called SVPMM. The traction return current is sometimes unbalanced owing to the ill-contact of SVPMM. In this paper, we propose a diagnosis method based on a short-circuited current(Icc), trimming capacitors and traction return current measured by Korail inspection vehicles. Whether Icc is good or bad depends not only on the presence of trimming capacitors but also on the unbalance of the traction return current.

• Journal of the Korean Society of Safety
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• v.26 no.6
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• pp.13-19
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• 2011

The purpose of this study is to examine the cause of damage to electrolytic capacitors and to present the heat generation mechanism in order to prevent the occurrence of similar problems. From the analysis results of electrolytic capacitors collected from accident sites, the fire causing area can be limited to the primary power supply for the initial accident. From the tests performed by applying overvoltage, surge, etc., it is thought that the fuse, varistor, etc., are not directly related to the accidents that occurred. The analysis of the characteristics using a switching regulator showed that the charge and discharge characteristics fell short of standard values. In addition, it is thought that heated electrolytic capacitors caused thermal stress to nearby resistances, elements, etc. It can be seen that the heat generation is governed by the over-ripple current, application of AC overvoltage, surge input, internal temperature increase, defective airtightness, etc. Therefore, when designing an electrolytic capacitor, it is necessary to comprehensively consider the correct polarity arrangement, appropriate voltage application, correct connection of equivalent series resistance(ESR) and equivalent series inductance(SEL), rapid charge and discharge control, sufficient margin of dielectric tangent, etc.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.61 no.4
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• pp.186-191
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• 2012

DC Bus Electrolytic capacitors have been widely used in power conversion system because they can achieve high capacitance and voltage ratings with volumetric efficiency and low cost. This type of capacitors have been traditionally used for filtering, voltage smoothing, by-pass and other many applications in power conversion circuits requiring a cost effective and volumetric efficiency components. Unfortunately, electrolytic capacitors are some of the weakest components in power electronic converter. Many papers have proposed different methods or algorithms to determinate the ESR and/or capacitance C for fault diagnosis of the electrolytic capacitor. However, both ESR and C vary with frequency and temperature. Accurate knowledge of both values at the capacitors operating conditions is essential to achieve the best reference data of fault judgement. According to parameter analysis, the capacitance increases with temperature and the ESR decreases. Higher frequencies make the ESR and C to decrease. Analysis results show that the proposed electrolytic capacitor parameter estimation technique can be applied to reference signal of capacitor diagnosis systems successfully.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.16 no.3
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• pp.207-213
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• 2003

The Sr$\_$0.7/Bi$\_$2.6/Ta$_2$O$\_$9/(SBT) thin films are deposited on Pt-coated electrode(Pt/TiO$_2$/SiO$_2$/Si) using RF magnetron sputtering method. The structural and electrical properties of SBT capacitors were influenced with annealing atmosphere. In the XRD pattern, the SBT thin films in all annealed atmosphere had (105) orientation. In the SEM images, Bi-layered perovskite phase was crystallized in all annealing atmosphere and grain largely grew in oxygen annealing atmosphere. The maximum remnant polarization and the coercive electric field in oxygen annealing atmosphere are 12.40[${\mu}$C/cm$^2$] and 30[kV/cm] respectively. The dielectric constant and leakage current density of capacitors annealed oxygen atmosphere are 340 and 2.13${\times}$10$\^$-9/ [A/cm$^2$] respectively. The fatigue characteristics of SBT capacitors did not change up to 10$\^$10/ switching cycles.

• Journal of Electrical Engineering and Technology
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• v.8 no.4
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• pp.808-812
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• 2013

Multilayer capacitors with high ripple current and high capacitance were manufactured. The electrical properties of these capacitors were characterized for potential application for DC-link capacitors in hybrid electric vehicle inverters. Internal electrode structures were designed to achieve high capacitance and reliability. A single multilayer capacitor showed $0.46{\mu}F/cm^3$ of capacitance, 0.65% of dielectric loss, and 1450 V to 1650 V of dielectric breakdown voltage depending on the design of the internal electrode. The capacitor module designed with several multilayer capacitors gave a total capacitance of $450{\mu}F$, which is enough for hybrid electric vehicles. In particular, an equivalent series resistance of $4.5m{\Omega}$ or less will result in 60 $A_{rms}$, thereby reaching the allowed ripple current for hybrid electric vehicles.

• Journal of Power Electronics
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• v.17 no.3
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• pp.653-663
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• 2017

Multilevel active neutral-point-clamped (ANPC) converter combines the advantages of three-level ANPC converter and multilevel flying capacitor (FC) converter. However, multilevel ANPC converter often suffers from capacitor voltage balancing problems. In order to solve the capacitor voltage balancing problems for five-level ANPC converter, phase-shifted pulse width modulation (PS-PWM) is used, which generally provides natural voltage balancing ability. However, the natural voltage balancing ability depends on the load conditions and converter parameters. In order to eliminate voltage deviations under steady-state and dynamic conditions, the active voltage-balancing control (AVBC) methods of floating capacitors and dc-link capacitors based on PS-PWM are proposed. First, the neutral-point current is regulated to balance the neutral-point voltage by injecting zero-sequence voltage. After that, the duty cycles of the redundant switch combinations are adjusted to balance the floating-capacitor voltages by introducing moderating variables for each of the phases. Finally, the effectiveness of the proposed AVBC methods is verified by experimental results.

• Journal of Power Electronics
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• v.18 no.1
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• pp.116-128
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• 2018

Conventionally, in order to reduce the ac components of the dc-link capacitors of the two-level Half-Bridge Voltage Source Inverter (HB-VSI), high dc-link capacitances are required. This necessitates the employment of short-lifetime and bulky electrolytic capacitors. In this paper, an analysis for the performance of low dc-link capacitances-based HB-VSI is presented to elucidate its ability to generate an enhanced fundamental output voltage magnitude without increasing the voltage rating of the involved switches. This feature is constrained by the load displacement factor. The introduced enhancement is due to the ac components of the capacitors' voltages. The presented approach can be employed for multi-phase systems through using multi single-phase HB-VSI(s). Mathematical analysis of the proposed approach is presented in this paper. To ensure a successful operation of the proposed approach, a closed loop current controller is examined. An expression for the critical dc-link capacitance, which is the lowest dc-link capacitance that can be employed for unipolar capacitors' voltages, is derived. Finally, simulation and experimental results are presented to validate the proposed claims.

• Journal of IKEEE
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• v.13 no.2
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• pp.194-199
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• 2009

In this study, ultra high-voltage (170kV AC), reliable 80pF mica capacitors for partial discharge system application were investigated. For capacitors design, Program was developed to sampling of series and parallel parameters. Mica was used as the dielectric of the capacitors. Using the conservative design rule, over 3 individual 50$\mu$m thick mica sheets with a size of 30mm$\times$35mm were used with lead foils to form a parallel capacitor element and 20 mica sheets were interleaved with lead foils to form a series stack of parallel capacitor element to meet the requirements of the capacitors. The dimension of the fabricated 80pF capacitor for 17kV AC were 90mm$\times$90mm. The high-frequency characteristics of the capacitance (C) and dissipation factor (D) of the developed capacitors were measured using a capacitance meter. The developed capacitor exhibited C of 79.5pF, had D of 0.001% over the frequency ranges of 150kHz to 50MHz, had a self-resonant frequency of 65MHz.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.13 no.3
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• pp.48-55
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• 1999

Ths paper presents an optimization method which determines locations and size of capacitors simultaneously while minimizing power losses and improving voltage profile in radial distribution systems. Especially, the cost function associated with capacitor pla.cerrent is considered as step function due to banks of standard discrete capacities. Genetic algorithms(GA) are used to obtain efficiently the solution of the cost function associated with capacitors which is non-continuous and non-differentiable function. The strings in GA consist of the node nwnber index and size of capacitors to be installed. The length mutation operator, which is able to change the length of strings in each generation, is used. The proposed Jrethod which determines locations and size of capacitors simultaneously can reduce power losses and improve voltage proftle with capacitors of minimum size. Its efficiency is proved through the arolication in radial distribution systems.ystems.