• 대한전기학회논문지:전기물성ㆍ응용부문C
• /
• 제52권1호
• /
• pp.35-41
• /
• 2003

In this paper statistics on the radiation field waveforms produced by stepped leaders just prior to lightning return strokes were described. As a parameter of stepped leader pulse characteristics, the time interval between the final leader pulse and return stroke peak, the pause time between stepped leaders, the ratio of the final leader peak to the return stroke peak and the stepped leader pulse width at half maximum were examined. The average time intervals between the final leader pulse and return stroke peak were about 16.2 and 14.8$mutextrm{s}$ for the positive and negative polarities, respectively. When the stepped leader approaches closely to ground, the time interval between leader steps was decreased and the mean value was about 17$mutextrm{s}$, and the present results were in reasonable agreement with the data observed in Florida and Japan. The large fraction of the ratios of the final stepped leader pulse to the lightning return stroke peak were distributed over the range from 5 to 35% and in average the ratio of the final leader pulse to the return stroke peak was 17.4$\pm$11.9% for the positive and 18.5$\pm$9.4% for the negative electric field waveforms. In addition, the mean pulse widths at half maximum of the stepped leaders are 1.4Us with a standard deviation of 0.9 for the positive Polarity and 2.2us with a standard deviation of 1.2 for the negative polarity, respectively.

• 전기학회논문지
• /
• 제56권8호
• /
• pp.1503-1510
• /
• 2007

To implement a high-precision lightning tracking system utilizing TDOA measurements, high-speed data acquisition and precise timing synchronization between ground sensors should be achieved. At the same time, considering the size of digitizer's memory, the data memory needs to be managed so that only the sampled data around the occurrence of stepped leader pulse is stored. This paper presents a detection-and-acquisition system for lightning signals that is the main equipment of ground sensor in lightning tracking system. GPS clock module is used to get precise timing synchronization and the 500MHz high speed digitizer is employed. In order to detect the leading edge of the lightning pulse and save the sampled data and its timing, lightning detection module is implemented and multi-record method is employed in the proposed system. Field experiment results show that the proposed system can detect and save the lightning signal efficiently.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2000년도 하계학술대회 논문집 C
• /
• pp.2002-2004
• /
• 2000

The discharge processes in electro-negative gases with non-uniform field gape are composed of the formation of pulsed streamer corona, the transition of the streamers into leader step, the temporal development of the leader channel, and the stepped propagation of leader through the gap. In this paper, the first corona inception characteristics in $SF_6$ gas and $SF_{6}-N_{2}$ mixtures, related to the propagation of loader and the space charge effect, were experimentally investigated with positive and negative transient impulse voltages.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2000년도 하계학술대회 논문집 C
• /
• pp.1996-1998
• /
• 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.

• Journal of Electrical Engineering and Technology
• /
• 제5권2호
• /
• pp.329-336
• /
• 2010

The paper describes the electrical and optical properties of underwater discharges in highly inhomogeneous electric fields caused by 1.2/50 ${\mu}s$ impulse voltages as functions of the polarity and amplitude of the applied voltage, and various water conductivities. The electric fields are formed by a point-to-plane electrode system. The formation of air bubbles is associated with a thermal process of the water located at the tip of the needle electrode, and streamer coronas can be initiated in the air bubbles and propagated through the test gap with stepped leaders. The fastest streamer channel experiences the final jump across the test gap. The negative streamer channels not only have more branches but are also more widely spread out than the positive streamer channels. The propagation velocity of the positive streamer is much faster than that of the negative one and, in fact, both these velocities are independent of the water conductivity; in addition the time-lag to breakdown is insensitive to water conductivity. The higher the water conductivity the larger the pre-breakdown energy, therefore, the ionic currents do not contribute to the initiation and propagation of the underwater discharges in the test conditions considered.

• 한국항공우주학회지
• /
• 제31권9호
• /
• pp.110-120
• /
• 2003

고공을 운항하는 항공기는 대기중의 자연현상에 의해 낙뢰에 노출되게 된다. 낙뢰 피해는 개발초기에는 목재 항공기의 절연파괴에 의한 손상과 화재등이 있었으며 알루미늄의 보급으로 전금속체 항공기가 개발되었지만 연료탱크의 화재 문제라든지 낙뢰 사고는 계속 발생하였다. 이에 NACA에서는 1938년 문제를 제기하고, 인공 낙뢰에 대한 연구를 시작하였다. 이어 FAA에서는 낙뢰보호에 대한 인증을 위해 감항기준을 제정하고 SAE에 낙뢰에 대한 항공기의 보호를 위한 시험대책 연구를 의뢰하여 낙뢰를 모사한 시험 전류, 전약 파형을 제시하여 항공기의 낙뢰보호, 인증에 활용하고 있다. 이 글에서는 낙뢰의 메커니즘 분석을 통한 항공기에 대한 낙뢰의 영향을 제시하고 특히 항공기 안전사고의 중요한 요인으로 대두되고 있는 항공기에 대한 낙뢰의 직접영향에 대한 사례를 분석하고 인증기준과 시험 전류 및 전압파형, 낙뢰 피격부위를 열거하여 개발항공기 및 비행체에 대한 인증에 활용되도록 하였다.

• KIEE International Transactions on Electrophysics and Applications
• /
• 제11C권4호
• /
• pp.120-126
• /
• 2001

For the past five years, Inha University has been observing the electric fields produced by cloud-to-ground return strokes. This paper presents the summary of most recent results. Statistics on the zero-to-peak rise time, the zero-to-zero crossing time and the amplitude ratio of the second peak in the opposite polarity to the first peak were examined. The radiation electric fields produced by distant cloud-to-ground return strokes were substantially same pattern. The first return stroke field starts with a slowly increasing front and rises abruptly to peak. The rising portions of the electric fields produced by cloud-to-ground return strokes last 1 $mutextrm{s}$ to a few $mutextrm{s}$. The mean values of the zero-to-peak rise times of electric fields were 5.72 $mutextrm{s}$ and 4.12 $mutextrm{s}$ for the positive and the negative cloud-to-ground return strokes, respectively. The mean of the zero-to-zero crossing time for the positive return strokes was 29.48 $mutextrm{s}$ compared with 38.54 $mutextrm{s}$ for the negative return strokes. The depths of the dip after the peak of return stroke electric fields also have the dependence on the polarity of cloud-to-ground return stroke, and the mean values for the positive and negative cloud-to-ground return strokes were 33.55 and 28.19%, respectively.

• Journal of KIEE
• /
• 제11권1호
• /
• pp.32-40
• /
• 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.

• 대한전기학회논문지:전기물성ㆍ응용부문C
• /
• 제53권6호
• /
• pp.330-336
• /
• 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.