• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.8
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• pp.2064-2070
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• 1995

Characteristics of thermal flow stratification were studied experimentally by using the small scale pressurizer-surge line model. Thermal flow stratifications in the horizontal section of surge line were analyzed by the relation between the maximum temperature difference at any cross section in surge line and the Froude number representing the boundary conditions, i.e., in/out surge flow velocity and temperature difference of system. Thermal flow stratifications in outsurge flow decreased inversely proportional to the Froude number and did not exist for Fr>1. In insurge flow thermal flow stratifications disappeared near Fr=1.5, but resulted in the higher temperature difference than the case of outsurge flow.

• KIEE International Transactions on Electrophysics and Applications
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• v.5C no.1
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• pp.1-7
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• 2005

This paper describes the lightning surge analysis model of extra high voltage GIS using EMTP. Various lightning current parameters were investigated in order to confirm the impact on the lightning surge analysis such as lightning current amplitude, waveform, size of GIS, tower footing resistance and surge arresters. The multi-story tower model and EMTP/TACS model were introduced for the simulation of dynamic arc characteristics. The margin between the maximum overvoltage and BIL of the GIS was about 10 percent and the margin between the maximum overvoltage and BIL of the transformer was 21 percent.

• Atmosphere
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• v.30 no.3
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• pp.249-256
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• 2020

We investigate regional differences in the characteristics of cold surges that occurred over the South Korea during winter season (December-February, 1981/1982~2017/2018). A significant regional contrast of cold surge characteristics exists and we found that this is closely related to the spatially inhomogeneous distribution of winter-mean climatological surface temperature in association with the complex topography of the Korean peninsula. For the regions of the temperature below -1℃ (Region1; R1), the frequency of cold surges is inversely proportional to the surface temperature almost linearly. In case of the regions above -1℃ (Region2; R2), cold surge frequency does not exhibit any clear dependency on the surface temperature. Duration and number of occurrences of cold surge between the two regions showed clear difference. Dynamical evolution of cold surges before the onset showed a sharp contrast between R1 and R2. In R1, cold surface air temperature (SAT) was already predominant over East-Asia before the onset and the cold temperature was sustained after the occurrence. On the contrary, warm SAT was predominant over East-Asia before the onset in R2. The SAT suddenly drops just after the cold surge occurrence. We present different origin of wave activity and propagation characteristics between the two types: Wave-activity flux (WAF) was relatively weaker and wave disturbances moved eastward in R1 along with the WAF mainly directing eastward. In case of R2, WAF was stronger and directing southeastward in the upstream of South Korea movement erasing predominant warmer air eventually causing sudden temperature drops over southern provinces over South Korea.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.21 no.7
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• pp.652-659
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• 2008

The nonlinear electrical properties and aging characteristics against surge stress of ZPCCL-based varistors were investigated for different sintering temperatures of the range $1240-1300^{\circ}C$. As the sintering temperature increased, the varistor voltage decreased from 732.2 to 53.8 V/mm, the nonlinear exponent decreased from 58.5 to 4.1, and the leakage current increased from $0.38{\mu}A$ to $46.5{\mu}A$. The varistors sintered at $1250^{\circ}C$ and $1260^{\circ}C$ exhibited the high stability against multiple surge, $150A/cm^2(8{\times}20{\mu}s)$. On the whole, the variation rate of electrical characteristics against impulse current stress was gradually increased in order of varistor voltage$\rightarrow$nonlinear exponent$\rightarrow$dissipation facto$\rightarrow$leakage current.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.8
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• pp.835-839
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• 2004

The surge characteristics of ZnO varistors consisting of $ZnO-{Pr}_6{O}_11-CoO-{Cr}_2{O}_3-{Er}_2{O}_3$ceramics were investigated at various sintering temperatures. As sintering temperature raises, the varistor voltage was decreased from 341.2 to 223.1 V/mm, the nonlinear exponent was decreased from 64,9 to 44.1. On the other hand, the leakage current exhibited a minimum(0.64 $\mu$A) at 134$0^{\circ}C$, The clamping capability was slightly deteriorated with increasing sintering temperature. On the whole, the ZPCCE-based ZnO varistors exhibited good clamping voltage characteristics as exhibiting the clamping voltage ratio of 1.85 ∼ 1.92 approximately at surge current of 100 A.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.07a
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• pp.315-317
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• 2005

The microstructure, electrical, and degradation characteristics against impulse current of ZPCCL-based varistors were investigated with various sintering temperature in the range of $1240\sim1300^{\circ}C$. The densification of varistors was improved, but the nonlinearity was deteriorated with increase of sintering temperature. The varistors sintered at $1250^{\circ}C$ and $1260^{\circ}C$ exhibited high stability against surge stress. On the whole, the variation of characteristics of varistor for surge stress was increased in order of varistor voltage$\rightarrow$nonlinear exponent$\rightarrow$dissipation factor$\rightarrow$leakage current.

• Proceedings of the KIPE Conference
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• 2001.07a
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• pp.197-200
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• 2001

This paper presents a PWM buck AC-AC converter with instantaneous compensation for input voltage sag and surge. The presented converter use commercial IGBT modules and its output voltage is regulated so as to remain constant AC output voltage. The feedforward control technique is also proposed to establish instantaneous duty level change whereby stable output voltage will be retained. This paper show the characteristics and control algorithm of the converter through various PSPICE simulations.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.9 no.3
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• pp.570-575
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• 2005

Malfunction by electrical surges is a serious problem on earth leakage current breakers(ELBs) used in a low voltage AC power system. In this paper, we tested ELBs according to IEC 61009-1 and KS C 4613 to analyze surge influence on ELB's malfunction. The test by application of surge voltage is specified both standards, but the test by application of surge current is specified only in IEC 61009-1. The experimental results showed that the ELBs used in this test are robust to surge voltage application, but the malfunction occurred to surge current application. Surge current is more frequent than surge voltage in actual situation. Therefore, ELBs should be tested by the surge current, and the domestic standard, KS C 4613, should includes a test procedure by the surge current application.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.22 no.9
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• pp.62-68
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• 2008

This paper describes the electrical characteristics of ZnO surge arresters associated with the variation of surrounding conditions. To investigate the deterioration behaviors of ZnO surge arresters due to lightning surges, 8/20[${\mu}s$], 2.5[kA] impulse currents were injected to the ZnO surge arrester under test. The leakage currents of ZnO surge arrester subject to power frequency AC voltage were measured in different surrounding temperature and wet conditions. As a result, it was found that the leakage current is increased and its asymmetry is pronounced as the number of injection of the impulse current and the ambient temperature increase. Also, in the wet test the outside leakage current flowing through the housing surface of the ZnO surge arrester is much larger than the intrinsic leakage current of ZnO surge arrester element. The results obtained in this work can be a lied as factors of improving the reliability and performance of monitoring system for surge arresters.

• The Proceedings of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.11 no.5
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• pp.44-52
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• 1997

Electronic circuits with semiconductor and IC are very weak against the surge voltage and currents. The surge protective devices for electronic circuit and AC power lines are becoming more widely used. It is possible to give rise to the malfunction of the earth leakage circuit breaker(ELB) due to the operation of surge protective devices, and the interruption of AC power lines on account of the malfunction of the ELB brings about several disadvantages such as low operation efficiency and reliability of electronic and informational systems, economical loss, and etc. The aim of the present work is to investigate the dead operation characteristics of the ELB against the surge voltages. The impulse generator of 10[kV) in an 1.2/ 50[~) voltage waveform was fabricated. The dead operation characteristics of the ELB applied by surge voltages were measured under the conditions of KS C 4613 and the test circuit with a varistor. As a consequence, the peak value of the zero-phase sequence circuit of the ELB is increased as the surge voltage and stray capacitance increase. All of the ELBs used in this work were satisfied with the lightning impulse dead operation test condition defined in KS C 4613. However one specimen only did not bring about dead operation in the condition of the test circuit with a varistor. There is high possibility that a large portion of the ELB installed at the AC power lines with the surge protective devices bring about the dead operation.