• Bulletin of the Korean Chemical Society
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• v.24 no.3
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• pp.369-376
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• 2003

Coulson (ZINDO), Mulliken $(MP2/6-31G^*)$ and Natural $(MP2/6-31G^*)$ population analyses of several large molecules were performed by the Fragment Reassociation (FR) method. The agreement between the conventional ZINDO (or conventional MP2) and FR-ZINDO (or FR-MP2) charges of these molecules was excellent. The standard deviations of the FR-ZINDO net atomic charges from the conventional ZINDO net atomic charges were 0.0008 for $C_{10}H_{22}$ (32 atoms), 0.0012 for $NH_2-C_{16}O_2H_{28}-COOH$ (53 atoms), 0.0014 for $NH_3^+-C_{16}O_2H_{28}-COOH$ (54 atoms), 0.0017 for $NH_2-C_{16}O_2H_{28}-COO^-$ (52 atoms), 0.0019 for $NH_3^+-C_{16}O_2H_{28}-COO^-$ (53 atoms), 0.0024 for a conjugated model $(O=CH-(CH=CH)_{15}-C=O-(CH=CH)_{12}-CH=CH_2)$, 118 atoms), 0.0038 for aglycoristocetin $(C_{60}N_7O_{19}H_{52}^+$, 138 atoms), 0.0023 for a polypropylene model complexed with a zirconocene catalyst $(C_{68}H-{121}Zr^+$, 190 atoms) and 0.0013 for magainin $(C_{112}N_{29}O_{28}SH_{177}$, 347 atoms), respectively. The standard deviations of the FR-MP2 Mulliken (or Natural) partial atomic charges from the conventional ones were 0.0016 (or 0.0016) for $C_{10}H_{22}$, 0.0019 (or 0.0018) for $NH_2-C_{16}O_2H_{28}-COOH$ and 0.0033 (or 0.0023) for $NH_3^+-C_{16}O_2H_{28}-COO^-$, respectively. These errors were attributed to the shape of molecules, the choice of fragments and the degree of ionic characters of molecules as well as the choice of methods. The CPU time of aglycoristocetin, conjugated model, polypropylene model complexed with zirconocene and magainin computed by the FR-ZINDO method was respectively 2, 4, 6 and 21 times faster than that by the normal ZINDO method. The CPU time of $NH_2-C_{16}O_2H_{28}-COOH\;and\;NH_3^+-C_{16}O_2H_{28}-COO^-$ computed by the FR-MP2 method was, respectively, 6 and 20 times faster than that by the normal MP2 method. The largest molecule calculated by the FR-ZINDO method was B-DNA (766 atoms). These results will enable us to compute atomic charges of huge molecules near future.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1992.05a
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• pp.140-143
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• 1992

This paper deals with the dielectric behaviors of $SF_{6}$ gas and prebreakdown growth caused by lightning impulse voltages in inhomogeneous field perturbed with a fixed needle-shaped protrusion on the electrode. The measuring interpretation of the external current induced by moving charges is described. The temporal growth of prebreakdown is obserbed by using a shunt and photomultiplier. The prebreakdown processes are initiated by the first streamer corona at a needle protrustion, the flashover of the main gap in the positive polarity is very sensitive to the local field and propagates into the gap with the leader mechanism. It is found that the dependence of the prebreakdown phenomena on the polarity of applied voltages is caused by the effect of space charges. In addition, the proposed measuring techniques are very useful to perform the measurements of avalanche currents, corona discharges in inhomogeneous fields ad partial discharges in voids.

• Proceedings of the KIEE Conference
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• 2006.07c
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• pp.1517-1518
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• 2006

This paper describes the design and fabrication of a partial discharge(PD) analyzer to evaluate insulation performance for low-voltage electrical and electronic devices. The analyzer consists of an adjustable AC power supply, a coupling network, an amplifier, a shielding encloser, a sample-hold (S/H) circuit and a data acquisition (DAQ) board. The analyzer holds the height of PD pulse for $10{\mu}s$ by the S/H circuit, and this makes possible to measure PD pulses having fast rise and short duration by a low speed analog-to-digital (A/D) converter. The data are transmitted to the personal computer through the DAQ board, and the designed analysis program calculate apparent charges, discharge inception and extinction voltages.

• Proceedings of the KIEE Conference
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• 1992.07b
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• pp.980-982
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• 1992

This paper deals with the dielectric behaviors of $SF_6$ gas and prebreakdown growth caused by lightning impulse voltages In inhomogeneous field perturbed with a fixed needle-shaped protrusion on the electrode. The measuring interpretation of the external current induced by moving charges is described. The temporal growth of prebreakdown is observed by using a shunt and photomultiplier. The prebreakdown processes are initiated by the first streamer corona at a needle protrusion, the flashover of the main gap in the positive polarity is very sensitive to the local field and propagates into the gap with the leader mechanism. It Is found that the dependence of the prebreakdown phenomena on the polarity of applied voltages is caused by the effect of space charges. In addition, the proposed measuring techniques are very useful to perform the measurements of avalanche currents, corona discharges in inhomogeneous fields and partial discharges in voids.

• Journal of Electrical Engineering and Technology
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• v.10 no.1
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• pp.344-354
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• 2015

In order to study the development of partial discharge (PD) under typical protrusion defects in gas-insulated switchgear, we applied step voltages on the defect and obtained the ${\varphi}-u$ and ${\varphi}-n$ spectrograms of ultra-high frequency (UHF) PD signals in various PD stages. Furthermore, we extracted seven kinds of features to characterize the degree of deterioration of insulation and analyzed their values, variation trends, and change rates. These characteristics were inconsistent with the development of PD. Hence, the differences of these features could describe the severity of PD. In addition, these characteristics could provide integrated characteristics regarding PD development and improve the reliability of PD severity assessment because these characteristics were extracted from different angles. To explain the variation laws of these seven kinds of parameters, we analyzed the relevant physical mechanism by considering the microphysical process of PD formation and development as well as the distortion effect generated by the space charges on the initial field. The relevant physical mechanism effectively allocated PD severity among these features for assessment, and the effectiveness and reliability of using these features to assess PD severity were proved by testing a large number of PD samples.

• Journal of Electrical Engineering and Technology
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• v.11 no.6
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• pp.1769-1776
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• 2016

For on-line partial discharge (PD) monitoring of rotating machines, a novel sensor is proposed, which can be installed on the power lead inside the terminal box of the machine. The sensor has been designed to have high capacitance, and minimal reflection of measured pulses. As a sensitivity of the sensor, transfer impedance $Z_t$ has been measured and compared to conventional coupler-type sensors. A simple method is presented for measuring $Z_t$ of coupler sensors, using a vector network analyzer and a practical lead-cable of rotating machine. Through this method, it became possible to measure the $Z_t$ of coupler sensors including the installation environment of them. The $Z_t$ of the proposed sensor is higher than that of same sized other conventional couplers at frequencies between 30 and 92 MHz. Another sensitivity test has been performed using a PD calibrator as a test pulse source. The proposed sensor has higher measured peak voltage than the conventional coupler type sensors when the same charges were input.

• Electrical & Electronic Materials
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• v.7 no.1
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• pp.32-41
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• 1994

In this study, the TSC spectroscopy has been applied to investigate the influence of structural change due to a process of curing reaction on the electrical properties of epoxy composites cured with acid-anhydride. Five TSC peaks appeared in -160-250[.deg.C]: in the low temperature region below glass transition temperature(T$\_$g/), three relaxation mode peaks due to action of side chains, substitution group or terminal groups have been observed, a peak associated with T$\_$g/, appeared in 110[.deg. C] and p peak due to ionic space charges located in 150[.deg.C]. Each peak was separated into elementary peaks by the partial polarization procedure, and the distribution of activation energy and relaxation time were analized to clearify the origin of each peak. Also, overaboundantly added hardener separated a .betha. peak near 10[.deg. C] into two peaks of .betha.$\_$1/(10.deg. C) and .betha.$\_$2/(20.deg. C) according to increasement of forming field, and the separated hardener was oxidated thermally with increasing surrounding temperatures. The expansion of the free volume need in molecular motion and the reduction of the structural packing density through thermal oxidation process increased TSC between .alpha. peak and .betha. peak and decreased T$\_$g/.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.48 no.5
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• pp.385-390
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• 1999

Surface corona discharge characteristics of a dc corona charged ferroelectric pellet barrier have been investigated experimentally. Electric charges stored on the surfaces of the ferroelectric pellets by a dc corona discharge provide partial electric fields on the surfaces of the ferroelectric pellets, which could generate surface corona discharges on the ferroelectric pellets. This system utilizes both the surface discharges on the ferroelectric pellet barrier and the corona discharge between corona tip and mesh electrode. Positive and negative dc voltages were applied to the tip to generate partial discharges, and corona currents were estimated to investigate the buildup charge on ferroelectric pellets as a function of the applied time and the charge relaxation time constants of ferroelectric pellets. As a result, in the case of the negative corona discharge with the ferroelectric pellet barrier, the mean corona current and ozone generation increase greatly, and the surface discharges on the ferroelectric pellets can be fenerated efficiently. It is also found that, charge relaxation time, dielectric constants offerroelectric pellets, polarity of applied voltage and applied time affected to the surface discharges among the ferroelectric pellets.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.503-504
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• 2006

This paper describes a low-level partial discharge(PD) testing that has been accepted as a non-destructive test method on insulation performance of electronic components. A comparative PD analysis combined with the Withstand Voltage Test (WVT) specified in IEC standards is carried out on high frequency switching transformers. The analysis shows that insulation degradation of the transformers under test progresses during the WVT. To avoid insulation degradation of the specimen, PD test has to be carried out at as low voltage as possible. In this study, the PD test on the transformers is performed in ranges from 50% to 70% of the test voltage specified in the WVT by measuring apparent charges below 1 pC. From the experimental results, it is expects that the low-level PD test is applicable for electronic components as a replacement of the WVT.

• Journal of Integrative Natural Science
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• v.7 no.1
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• pp.45-49
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• 2014

The (c-Jun N-terminal kinase 3) JNK3 is a potential therapeutic target for various neurological disorders. Here, a three dimensional quantitative structure-activity relationship (3D-QSAR) study on phenoxypyridine as JNK3 inhibitors was performed to rationalize the structural requirements responsible for the inhibitory activity of these compounds. The comparative molecular field analysis (CoMFA) using different partial atomic charges, was employed to understand the structural factors affecting JNK3 inhibitory potency. The Gasteiger-Marsili yielded a CoMFA model with cross-validated correlation coefficient ($q^2$) of 0.54 and non-cross-validated correlation coefficient ($r^2$) of 0.93 with five components. Furthermore, contour maps suggested that bulky substitution with oxygen atom in $R^3$ position could enhance the activity considerably. The work suggests that further chemical modifications of the compounds could lead to enhanced activity and could assist in the design of novel JNK3 inhibitors.