• Proceedings of the KIEE Conference
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• 2000.07c
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• pp.1996-1998
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• 2000

In this paper, the electric and magnetic field waveforms produced by cloud-to-groud lightning discharges were measured and statistically analyzed. The measuring system used to measure the electric and magnetic fields is consisted of the hemisphere electric field sensor, the loop magnetic field sensor and the data acquisition system. The stepped leader is appeared before the return stroke. Some parameters of the electric and magnetic fields produced by the stooped leaders in cloud-to-ground lightning discharges were investigated.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.53 no.6
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• pp.330-336
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• 2004

In this work, in order to obtain the detailed information about lightning electromagnetic pulses, the electric fields radiated from multiple lightning return strokes were measured and analyzed statistically. The electric field measuring system consists of a hemisphere antenna of 30cm in diameter, integrator and data acquisition device, and its frequency bandwidth ranges from 200Hz to 1.56MHz, and the sensitivity is 0.96㎷/V/m. The electric field signals are digitized every 200ns with the transient signal analyzer having the resolution of 12-bit and the recording length of 5 kilowords and are registered at personal computer. As a result, the electric fields produced by the first return stroke begin with a slow initial part or front, which starts just after or during the last stepped leader. On the average the rise times of the electric fields for the positive first, second and third strokes are 4.21${\mu}\textrm{s}$, 3.94${\mu}\textrm{s}$ and 2.75${\mu}\textrm{s}$, respectively, and those for the negative first, second and third strokes are 3.46${\mu}\textrm{s}$, 3.15${\mu}\textrm{s}$ and 2.79${\mu}\textrm{s}$, respectively. The zero-crossing times of the electric fields for first return strokes range from about 10 to 80${\mu}\textrm{s}$. The mean zero-crossing times for subsequent return strokes are shorter than those for first lightning return strokes.

• Journal of KIEE
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• v.11 no.1
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• pp.32-40
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• 2001

This paper presents the detailed statistics on radiation field signatures associated with multiple-intracloud lightning discharges. A transient signal recording system was used to measure the electric and magnetic fields produced by lightning flashes. The measurements were made in th summers of 1995 through 1999, and the location of the observation station was in Inchon on the coast of the Yellow Sea in Korea(37$^{\circ}$25'N, 126$^{\circ}$ 39'E). Most of lightning flashes typically contains between two and five strokes. The individual intracloud stork radiation fields were the bipolar pulse. On the average, the ratio of the peak of the second stroke to the first stroke peak was 75.1$\pm$40.1% for the negative, and a fraction of the subsequent stroke peaks were higher than the first stroke peak. The greater the number of the subsequent stroke order, less time separations between strokes were produced. The mean of the depth of the dip was 81.2$\pm$27.9% for the positive polarity and 75.9$\pm$24.4% for the negative. The depth of the dip increased for the positive bipolar pulses and decreased for the negative as the number of the stroke order increased.

• Proceedings of the KIEE Conference
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• 2000.07c
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• pp.1999-2001
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• 2000

Impulse breakdown voltage characteristics of sulphur-hexafluoride/nitrogen ($SF_{6}-N_{2}$) mixtures were presented. The applied voltages were the positive and negative lightning impulse (1.2/44${\mu}s$) and oscillating impulse ($0.4{\mu}s$/2.08MHz) voltages. The predischarge current was observed to clarify the breakdown mechanism. The electrode system was consisted of plane to plane configuration with a needle-shaped protrusion whose length and diameter are 10mm and 1mm. The measurements were carried out at the gas pressure of mixtures up to 0.5MPa with nitrogen concentrations varying from 5 to 20%. The electrical breakdown in $SF_{6}-N_{2}$ mixtures develops with steplike pulses in leader mechanism. The minimum breakdown voltages for the negative lightning and oscillating impulse voltages were higher than those for the positive.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2005.05a
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• pp.57-60
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• 2005

This paper describes the experimental results of the pre-breakdown phenomena in $SF_6/CO_2$ mixtures under non-uniform electric fields caused by positive and negative lightning negative voltages. $SF_6/CO_2$ mixtures have an advantage of an environmental aspect and cost reduction, and safety aspects. In order to analyze the pre-breakdown processes in $SF_6/CO_2$ mixtures stressed by impulse voltages, pre-breakdown current and luminous signals were measured by a shunt and a photo-multiplier tube, respectively. Dielectric strengthes of $SF_6/CO_2$ mixtures were investigated. Additionally, characteristics of discharge channels were observed by high speed cameras and the physical properties were discussed. The pre-breakdown propagates with a stepwise process. The in to breakdown from the corona onset point in positive polarity was shorter than that in negative polarity. The time intervals of positive leaders are shorter than those of negative leaders, and the path of positive leader channel is zigzag.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.49 no.9
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• pp.533-540
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• 2000

Lightning impulse $(1.2/44[\mus])$ and damped oscillating impulse $(Osc./44[\mus])$ : 0.83[MHz]) breakdown characteristics in sulphur-hexafluoride/nitrogen (SF6-N2) mixtures were investigated. The predischarge currents were observed to clarify the breakdown mechanism. th experiments were carried out under nonuniform electric fields disturbed by a needle-shaped protrusion whose length and diameter are 10[mm] and 1[mm] at total gas pressure up to 0.5[MPa] with nitrogen concentrations varying from 5 to 20[%] in the mixture. The electrical breakdowns of SF6-N2 mixtures for both the positive and negative polarities develop with steplike pulses in leader mechanism and the breakdown voltage -time (V-t) characteristics were affected by the space charge. The voltage-time curves for the negative oscillating impulse voltage were extended over the longer time range. The minimum breakdown voltages for the negative lightning and oscillating impulse voltage were higher than those for the positive ones. in particular the positive breakdown voltages were independent of the gas pressure.

• Proceedings of the KIEE Conference
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• 2005.07c
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• pp.2140-2142
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• 2005

This paper presents the experimental results on the preliminary breakdown characteristics under a highly non-uniform electric field in $SF_6/CO_2$ gas mixtures. The impulse preliminary breakdown developments are investigated by the measurements of corona current and light emission images. As a result, the preliminary breakdown development mechanisms for both positive and negative polarities are same. The first streamer corona is initiated at the tip of needle electrode, and the leaders develop with a stepwise propagation and bridge the test gap. The pause time of leader pulses in the positive polarity is significantly shorter than that in the negative polarity. Also, the time interval between the first streamer corona onset and breakdown in the negative polarity was much longer than that in the positive polarity The discharge channel paths in the positive polarity were zigzag. On the other hands, the leader channel in the negative polarity was thicker than that in the positive polarity.

• 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.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.20 no.1
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• pp.85-90
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• 2006

This paper presents experimental results relating to the preliminary breakdown characteristics in $SF_6/CO_2$ gas mixtures under a highly non-uniform electric field. The impulse pre-breakdown developments are investigated by the measurements of corona current and light emission images. As a result, the preliminary breakdown development mechanisms for both the positive and negative polarities were fundamentally same. The first streamer corona was initiated at the tip of needle electrode, and the leaders developed with a stepwise propagation and bridged the test gap. The pause time of leader pulses in the positive polarity was significantly shorter than that in the negative polarity. Also, the time interval between the first streamer corona onset and breakdown in the negative polarity was much longer than that in the positive polarity. The discharge channel path in the positive polarity was zigzag, and the leader channel in the negative polarity was thicker and brighter than that in the positive polarity.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.22 no.12
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• pp.79-86
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• 2008

This paper presents the experimental results of impulse breakdown characteristics in $SF_6/N_2$ gas mixtures under a highly non-uniform electric field with a change in temperature. The test temperature ranges from -25[$^{\circ}C$] to 25[$^{\circ}C$]. The processes of impulse preliminary breakdown developments were analyzed by the measurements of current pulse and luminous signals. As a result, the temperature dependance of breakdown voltage for the negative polarity was much stronger than that for the positive polarity. When increasing the temperature, The leader stepping time for the negative polarity was shown to be longer than that for the positive polarity. The results presented in this paper can be used as a useful information in designing the gas insulation lines with prominent ability for lightning surge.