• The Transactions of the Korean Institute of Electrical Engineers C
• /
• v.53 no.5
• /
• pp.253-257
• /
• 2004

In order to analyze the frequency dependance of ground impedance in grounding grids for lightning and surge protection, a novel method for measuring the ground impedance as a function of frequency were experimentally investigated. The experiments were carried out in rectangular grounding grids with $6{\times}8$ conductors of 22 $mm^2$ buried at a depth of 0.5 m. The test current was injected by the variable frequency inverter whose frequency is linearly controlled for the established period in the range of 5∼500 KHz. The amplitude and phase of ground impedance were calculated from the waveforms of the test current and ground potential rise measured by the band-pass filter tuned in a specific frequency. The frequency dependence of ground impedance was mainly caused by the inductive current flowing through grounding conductors over the frequency of 100 KHz. The proposed measurement method of ground impedance would be applicable to evaluate the transient response characteristics in lightning protection grounding systems.

• Journal of Electrical Engineering and Technology
• /
• v.4 no.4
• /
• pp.531-537
• /
• 2009

Lightning has a broad frequency spectrum from DC to a few MHz. Consequently, the high frequency performance of grounding systems for protection against lightning should be evaluated, with the distributed parameter circuit model in a uniform soil being used to simulate grounding impedances. This paper proposes a simulation method which applies the distributed parameter circuit model for the frequency-dependent impedance of vertically driven ground rods by considering multi-layered soil structures where ground rods are buried. The Matlab program was used to calculate the frequency-dependent ground impedances for two ground rods of different lengths. As a result, an increase of the length of ground rod is not always followed by a decrease of grounding impedance, at least at a high frequency. The results obtained using the newly proposed simulation method considering multi-layered soil structures are in good agreement with the measured results.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.20 no.2
• /
• pp.81-88
• /
• 2006

In this study, the electric and magnetic fields measuring system were designed and fabricated to investigate the electric characteristics of lightning discharges. Frequency bandwidth of electric field measuring system ranges from 40[Hz] to 2.6[MHz] and its response characteristic is 2.1[(V/m)/mV]. Frequency bandwidth of magnetic field measuring system ranges from 300[Hz] to 1[MHz] and its response characteristic is 2.8[nT/mV]. Electric and magnetic fields due to intracloud lightning discharges were observed and their waveform parameters were statistically analyzed. As a result, waveform parameters of electric and magnetic fields are nearly independent of polarity. The mean rise times and the zero-crossing times of electric and magnetic fields are approximately $5.5[{\mu}s]\;and\;21[{\mu}s]$, respectively.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.23 no.4
• /
• pp.79-85
• /
• 2009

This paper describes the degradation properties of ZnO surge arresters impressed by lightning impulse currents. To investigate the deterioration behaviors of ZnO surge arresters due to lightning surges, the 8/20[${\mu}s$], 2.5[kA] standard lightning impulse currents were injected to the ZnO surge arrester under test. The power frequency AC and DC leakage currents flowing through the ZnO surge arresters with and without the injection of lightning impulse currents were measured. As a result, the leakage currents are increased and the asymmetry of the AC leakage current is pronounced as the number of injection of the impulse current increases. The ZnO grain of the surge arrester without the injection of lightning surges are uniform but the ZnO grain of the ZnO surge arrester with the injection of lightning impulse currents are deformed. Also, it was found that the decrease of the $Bi_2O_3$ due to the lightning impulse current leads to the lack of grain boundary layer and the current concentrated by the lack of grain boundary layer play an important role to degrade nonlinear property of ZnO surge arrester blocks.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.7 no.4
• /
• pp.300-309
• /
• 1996

The electric and magnetic fields radiated by lightning discharges are significantly changeable in amplitude and time, one of the topics concerning electromagnetic compatibility of modern electronic systems is the efficient and economic protection against transient voltages caused by not only by direct but also by nearly lightning strokes. In this paper, in order to obtain the detailed informations about lightning electromagnetic impulse waveforms, the electric and magnetic fields radiated by lightning discharges in the summer of 1995 were measured by a fast electric antenna and a loop-type magnetic field sensor, and their charac- teristics were presented and analyzed. The signals of the electric and magnetic fields were re- corded continuously by a transient digitizer having a resolution of 12 bit and a memory capacity of 5000 point and using a sampling time of 200 ns. The electric and magnetic field waveforms associated with lightning return strokes are significantly different with those of intracloud discharges. The magnetic fields radiated by intracloud lightning discharges have essentially the same waveforms as the electric field when the lightning discharhes are at distance of 50 km or more. Also the main frequency components of the electric and magnetic fields radiated by lightning discharges range from a few kHz to several hundred kHz.

• Journal of the Korean earth science society
• /
• v.24 no.3
• /
• pp.181-189
• /
• 2003

This study analyzes the results of thunderstorm data observed in the mid-western part of Japan during the winter of 1996-1997. There were 35 instances of thunderstorms with 4,426 instances of lightning detected during the observation period. This study estimates the frequency of lightning occurrence through classification of detected lightning into two types, and analyzes the relationship between lightning types and synoptic pattern. According to the analyzed results, cloud-to-cloud discharge and positive polarity occupied 78% and 42.3% of total discharge, respectively. It is rare for lightning to occur in the winter season, usually occuring during the night (midnight to 5 a.m.). Lightning frequently occurs when there is a prevailing synoptic wind from the norhwest. According to the analyzed results of multiplicity and multi-point lightning, the mean values of multiplicity and multi-point lightning are 1.4 and 1.2, respectively.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.24 no.1
• /
• pp.98-104
• /
• 2010

In order to evaluate the performance of a grounding system against lightning or fault currents including high frequency components, the grounding impedance should be considered rather than the steady state ground resistance. To evaluate the ground impedance, the frequency dependence of resistivity and relative dielectric constant of the soil have to be analyzed. This paper deals with the frequency dependence of the resistivity and relative dielectric constant of three types of soil on water content. As a result, the resistivity of soil is getting lower with increasing of water content. It is nearly independent of the frequency in the range less than 1[MHz], and is decreased over the frequency range above 1[MHz]. On the other hand, the relative dielectric constant is rapidly decreased with the frequency in the range less than 1[MHz], but it is nearly independent on the frequency over the range of 1[MHz]. It was found from the experiments that the frequency-dependant resistivity and relative dielectric constant of soil should be considered when designing the grounding systems for protection from lightning or switching surges.

• Journal of the Korean earth science society
• /
• v.31 no.7
• /
• pp.749-761
• /
• 2010

A relationship between cloud-to-ground lightning and rainfall was investigated by using the two-years (2006-2007) summer lightning data and the automatic weather stations (AWSs) data of the Korea Meteorological Administration. The negative lightning occurred at the core of highly concentrated convection, which is often accompanied with heavy rains. Whereas most positive lightning occurred at the anvil cloud with low density and light rains. The rainfall intensity is strongest when the negative and positive lightning occurred concurrently, and one with lightning is much stronger than that without lightning. A portion of the positive lightning of the total lightning was less than 10% during summer seasons, and the lightning without rains was about 34%. The rain rate was strongly correlated with the negative flash rate, and the correlation coefficients varied between 0.87 and 0.94 according to the co-location radius (5-15 km) of AWSs. Most of the lightning occurred 10 minutes before and/or concurrently occurred with rains. A portion of the convective rainfalls of the total rainfalls was at least 20% when we define the rainfalls with lightning as convective. The convective rainfall was greater during August than in June and July. In general, the portion of convective rainfalls showed a maximum diurnal variation during late afternoon as in the rains and lightning.

• Proceedings of the KIEE Conference
• /
• 1997.07e
• /
• pp.1824-1826
• /
• 1997

In this paper, in order to obtain statistical informations on lightning electromagnetic waveforms, electric field waveforms produced by lightning return strokes were measured and analyzed. The electric field measuring system consists of hemisphere antenna 30[cm] in diameter, integrator and data acquisition. system. The frequency bandwidth of the measuring system is 200[Hz] to 1.56[MHz], and the sensitivity is 0.96[mV/V/m]. The mean value of front time of electric field waveforms produced by positive lightning return strokes is 5.87[${\mu}s$], and that of negative is 4.12[${\mu}s$]. The mean values of zero-crossing time for positive or negative electric field waveforms are 35.00 and 26.61[${\mu}s$], respectively. The mean value of percentage dip-depth for positive electric field waveforms is 33.68[%], and that for negative is 28.36[%].

• Journal of Wind Energy
• /
• v.14 no.4
• /
• pp.50-56
• /
• 2023

With the abnormal weather phenomena caused by global warming, the frequency and intensity of lightning strikes are increasing, and lightning accidents are becoming one of the biggest causes of failures and accidents in offshore wind turbines. In order to secure generator operation reliability, effective and practical measures are needed to reduce lightning damage. Because offshore wind turbines are tall structures installed at sea, the possibility of direct lightning strikes is very high compared to other structures, and the role of surge protection devices to minimize damage to the electrical and electronic circuits inside the wind turbine is very important. In this study, a varistor, which is a key element for a class 1 surge protection device for direct lightning protection, was developed. The current density was improved by changing the varistor composition, and the distance between the electrode located on the varistor surface and the edge of the varistor was optimized through a simulation program to improve the fabrication process. Considering the combined effects of heat distribution, electric field distribution, and current density on the optimized varistor surface, silver electrodes were formed with a gap of 0.5 mm. The varistor developed in this study was confirmed to have an energy tolerance of 10/350 ㎲, 50kA, which is a representative direct lightning current waveform, and good protection characteristics with a limiting voltage of 2 kV or less.