• Bulletin of the Korean Mathematical Society
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• v.55 no.6
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• pp.1667-1690
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• 2018

We consider the minimum order of a graph G with a given lazy cop number $c_L(G)$. Sullivan, Townsend and Werzanski [7] showed that the minimum order of a connected graph with lazy cop number 3 is 9 and $k_3{\square}k_3$ is the unique graph on nine vertices which requires three lazy cops. They conjectured that for a graph G on n vertices with ${\Delta}(G){\geq}n-k^2$, $c_L(G){\leq}k$. We proved that the conjecture is true for k = 4. Furthermore, we showed that the Petersen graph is the unique connected graph G on 10 vertices with ${\Delta}(G){\leq}3$ having lazy cop number 3 and the minimum order of a connected graph with lazy cop number 4 is 16.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.697-700
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• 2001

In this paper, the structural and electrical properties of the Sr$_{1-x}$ Ca$_{x}$TiO$_3$ (0$\leq$x$\leq$0.2) (0$\leq$r$\leq$0.2)-based grain boundary layer ceramics were investigated by X-ray, SEM and V-I system. Increasing the Ca content, the average grain size and the lattice constant were decreased. The relative density of all specimens was >96%. The 2nd phase formed by thermal diffusing from the surface lead to a very excellent electrical properties, that is, $\varepsilon$$_{r}$>50000, tan$\delta$<0.05, $\Delta$C< $\pm$ 10%.\pm$ 10%.%.

• Proceedings of the KIEE Conference
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• 2001.07c
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• pp.1387-1389
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• 2001

In this paper, the microstructure and the dielectric properties of the $Sr_{1-x}Ca_xTiO_3$($0{\leq}x{\leq}0.2$)-based grain boundary layer ceramics were investigated. The 2nd phase formed by thermal diffusing from the surface lead to a very high apparent dielectric constant, ${\varepsilon}_r$ > 50000, and tan$\delta$ < 0.05, $\Delta$C < ${\pm}$ 10%.

• Proceedings of the KIEE Conference
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• 2001.07c
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• pp.1384-1386
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• 2001

In this paper, the structural and electrical properties of the $Sr_{1-x}Ca_xTiO_3$($0{\leq}x{\leq}0.2$)-based grain boundary layer ceramics were investigated by X-ray, SEM and V-I system. Increasing content of Ca, the average gram size and the lattice constant were decreased. The relative density of all specimens was > 96%. The 2nd phase formed by thermal diffusing from the surface lead to a very excellent electrical properties, that is, ${\varepsilon}_r$ > 50000, tan${\delta}$ < 0.05, $\Delta$C < ${\pm}$ 10%.

• Proceedings of the KIEE Conference
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• 2004.11d
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• pp.46-49
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• 2004

This test was performed to assess the correlation between insulation diagnostic tests and breakdown voltage strength of the stator winding of 6.6kV class induction motor in insulation deterioration condition which have been in service for 5 years after being installed in 1998. The insulation diagnostic tests include resistance, polarization index(P.I), dissipation factor(${\Delta}tan{\delta}$). maximum partial discharges(Qmax) and AC breakdown test. we evaluated the correlation between insulation diagnostic test and AC breakdown test for stator winding of high voltage induction motor.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.14 no.5
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• pp.397-404
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• 2001

This study describes the effect of γ-ray irradiation on the properties of insulation materials for low voltage cables in a nuclear power plant. The radiation effects were characterized by measuring OIT, FTIR, electrical properties of the irradiated specimens. As a result, they showed the decrease of OIT and the increase of chemical structural defects with the increase of γ-ray amount. Also, the electrical properties such as dielectrical constant, tan $\delta$ and current were changed by aging. These changes may come from the increase of chemical structural defects by $\delta$-ray irradiation.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.45 no.2
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• pp.294-300
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• 1996

In hydro-generator, a groundwall insulation of stator windings gradually deteriorates due to mechanical, thermal, electrical and environmental stresses. These stresses combine to result in loose windings, delamination of the stator insulation and/or electrical tracking of the endwinding, all of which can lead to stator insulation failures. Conventionally, off-line tests such as partial discharge measurement, DC/AC current and .DELTA.tan.delta. tests has been used for estimation of winding condition. However, off-line test requires large power supply and generator outage. In addition, major cause of insulation problems such as loose wedges and slot dischages may not be found with off-line diagnoses. This paper introduces the on-line partial discharge measurement techniques using frequency spectrum analyzer(FSA) for the generator stator windings. The experimental results from the UIAM #1 hydro-generator confirms a optimistic application of on-line generator diagnosis method as a reliable tool for evaluation of winding condition.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.11a
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• pp.34-37
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• 2001

In this study, the capacitance-voltage properties of (Sr$_{1-x}$ .Ca$_{x}$)TiO$_3$(0.05$\leq$x$\leq$0.20)-based grain boundary layer ceramics were investigated. The ceramics were fabricated by the conventional mixed oxide method. The sintering temperature and time were 1480~150$0^{\circ}C$ and 4 hours, respectively. The 2nd phase formed by the thermal diffusion of CuO from the surface leads to very excellent dielectric properties, that is, $\varepsilon$$_{r}$>50000, tan$\delta$<0.05, $\Delta$C<$\pm$10%. The capacitance is almost unchanged below about 20[V] but it decreases slowly about 20[V]. The results of the capacitance-voltage properties indicated that the grain boundary was composed of the continuous insulating layers.ulating layers.s.

• Proceedings of the KIEE Conference
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• 2003.07b
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• pp.783-785
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• 2003

This test was performed to assess the insulation deterioration condition of the stator winding of 3.3kV class induction motors which have been in service for 15 years after being installed in 1988. The insulation diagnostic tests include resistance, polarization index(P.I). dissipation factor(${\Delta}tan{\delta}$) and maximum partial discharges(Qmax). The results of diagnostic tests were compared to the visual inspection in overhaul.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.27 no.12
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• pp.847-851
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• 2014

The characteristics of dielectric constant and $tan{\delta}$ of low viscosity silicone oils with changing degree of polymerization were investigated. The result shows dipole loss mechanism at low temperature range. The dielectric loss in the range of low frequencies are predominantly of ionic nature with temperature increase. The peak of dielectric loss is the detrapping of the electrons which is were trapped in the localized level of the silicone oils at the frequency of 30 kHz. The increase of ionic conduction is attributed to the presence of ionizable oxidation products and their increased dissociation feature. The activation energy ${\Delta}H$ and dipole moment ${\mu}_d$ were increased whit increasing degree of polymerization.