• Transactions on Electrical and Electronic Materials
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• v.16 no.6
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• pp.317-322
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• 2015

The metal oxide varistor (MOV) is a major component of the surge protection devices (SPDs) currently in use. The device is judged to be faulty when fatigue caused by the continuous inflow of lightning accumulates and reaches the damage limit. In many cases, induced lightning resulting from lightning strikes flows in to the device several times per second in succession. Therefore, the frequency or the rate at which the SPD is actually exposed to stress, called a surge, is outside the range of human perception. For this reason, the protective device should be replaced if it actually approaches the end of its life even though it is not faulty at present, currently no basis exists for making the judgment of remaining lifetime. Up to now, the life of an MOV has been predicted solely based on the number of inflow surges, irrespective of the magnitude of the surge current or the amount of energy that has flowed through the device. In this study, nonlinear data that shows the damage to an MOV depending on the count of surge and the amount of input current were collected through a high-voltage test. Then, a failure prediction algorithm was proposed by preparing a look-up table using the results of the test. The proposed method was experimentally verified using an impulse surge generator

• Proceedings of the KIEE Conference
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• 2001.07c
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• pp.1724-1726
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• 2001

This paper deals with the characteristics of the potential rises of down-conductor due to lightning surge currents. Direct lightning strikes can cause high impulse currents to the lightning protection system(LPS) of a building. These high impulse currents have the front time as short as 1[${\mu}s$]. In this case, the induced voltages caused in a closed circuit inside the building can be very high and cause damage or submit people to electric hazard. So, the LPS has to be designed to ensure safety condition to person and acceptable levels of induced voltages to the electrical and electronic equipments. The results of the potential rises related to the bonding conditions between the grounding conductor and metal raceway and the type of down-conductors are introduced.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.16 no.5
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• pp.90-96
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• 2002

The AC power lines and signal lines of info-communication networks are muted on overhead poles and are exposed to lightning strikes. Due to the potential difference between groundings of the AC power lines and telecommunication lines, the electronic equipments connected to the telecommunication lines can easily be damaged by lightning surges. In this work, in order to develop the reliable ways to protect information and communication facilities from lightning surges, the reliability and performance of surge protective devices were experimentally investigated in actual-sized test circuit. The operation behaviors of surge protective devices against lightning surges from the AC power lines and telecommunication lines and the coordination effects of SPD installation method were evaluated. As a consequence, it was confirmed that the bypass arrester and common grounding system is very effective.

• Journal of the Korean earth science society
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• v.30 no.2
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• pp.210-222
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• 2009

Lightning data, observed from total lightning detection system (TLDS) of KMA, for the recent five years (2002-2006) have been analyzed for temporal and spatial characteristics of frequency, intensity, duration, and flash rate. Lightning frequency varies largely with years (most frequent in 2006) and the lightning during the summer accounts for 75% of total flashes and only 0.6% of lightnings strike in cold season. In rainy season (JJAS), the ratio of positive flashes to negative ones is as low as 0.15, but it increases up to 0.98 in February. The seasonal variation of lightning duration is strongly linked with lightning occurrences, whereas flashes rates show weak seasonal variability. In a daily scale, lightning, on average, occurs more often at dawn (2 am, 5-7 am) and in the mid-afternoon (15 pm), and the lightning at dawn (around 5 am) is most intense during the day. The western inland areas md the West/South Sea show high lightning density during JJAS, whereas eastern part and the East Sea exhibit a low density of lightning. Considering the low ratio of positive flashes (0.15) for the whole analysis domain during summer period, Chungnam and Jeonbuk areas have a high ratio of flashes over 0.4. However, these should be analyzed with much caution because weak positive cloud-to-cloud discharges can be regarded as cloud-to-ground flashes. The western inland also exhibits long annual flash hours (15-24). And the W3st Sea has high flash rates as a result of large density and low flash hours. The most frequent time of lightning occurrence over most inland areas lies between mid-afternoon and early-evening, whereas mountainous and coastal areas, and the northern Kyoungki and Hwanghae provinces show the maximum lightning strikes in the morning and at dawn, respectively.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.3
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• pp.251-262
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• 2021

The airworthiness certification of lightning indirect effects becomes an important issue in personal air vehicles (PAVs), which are being actively developed around the world. PAVs are very vulnerable to lightning strikes, because of miniaturization, use of the electric engines, composite materials, and application of unmanned navigation systems. In this study, we first examined various steps of certifications for lightning indirect effects shown in AC 20 136B issued by the Federal Aviation Administration (FAA). We then applied certification guidelines for equipment transient design level listed in RTCA DO 160G Section 22 to PAVs and investigated lightning transient environments inside the PAVs. We also analyzed the aircraft level tests specified in SAE ARP 5416A by using electromagnetic computational analysis software EMA3D. Finally, we analyzed the actual transient level for PAVs and derived the data necessary for conformity certification.

• Proceedings of the KIEE Conference
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• 2006.07a
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• pp.157-158
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• 2006

This paper describes the overvoltage of branch line in underground distribution systems when the direct lightning surge strikes on conductor of overhead line. Distribution systems are very complex because that includes so many branch lines, transformers, switches and so on. Therefor model systems consist of overhead distribution lines, underground cable include branch lines, lightning source and switches. Those are established by EMTP/ATPDraw. Simulation analyzes surge behavior on branch lines considering various conditions in underground distribution systems. Simulation results shoe overvoltage with location in various cases.

• Proceedings of the KIEE Conference
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• 2006.11a
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• pp.148-150
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• 2006

This paper describes the overvoltage at the branch line in underground distribution systems when the direct lightning surge strikes on conductor of overhead line. Distribution systems are very complex because it includes many branch lines, transformers, switches and so on. Therefore model system consists of overhead distribution lines, underground cable include branch lines, lightning source and switches. Analysis are performed using EMTP to understand and evaluate the surge behavior on branch lines considering various conditions in underground distribution systems. Simulation results show overvoltage with location in various cases. It is evaluated that result will be used to establish protection methods in actual underground distribution systems.

• Proceedings of the KIEE Conference
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• 1998.07e
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• pp.1675-1677
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• 1998

It is currently increasing to use surge protection devices in the protection of various electronic circuits from the transient overvoltages such as lightning strikes and switching surges. For this reason, the simulation methods, which can easily predict the protection performance of the devices, are strongly required in order to design the adequate surge protection circuits in lightning surge cut-off performance and economic aspects. This paper deals with ZnO varistor modeling method for designing a surge protection circuit and suggests the Pspice simulation model which takes the characteristic of varying clamping voltage into consideration during the time-to-crest, in range of $8{\sim}30{\mu}s$, of surge current applied to a ZnO varistor. The ZnO varistor Pspice simulation data introduced in this paper has produced almost same values as the measured results experimentally.

• Journal of Aerospace System Engineering
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• v.15 no.3
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• pp.45-56
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• 2021

Demand for UAM (Urban Air Mobility) aircraft is rapidly increasing in countries around the world due to the problem of traffic congestion in urban areas. Through research and development, various e-VTOL aircraft concepts are being prepared for commercialization, for which airworthiness certification is required, since it is a manned transportation mode for people to board. Factors that pose a fatal threat to the safe operation of UAM aircraft include lightning strikes that can cause damage to structures and disturb the navigation system, as well as icing that impairs flight stability. Since the current UAM aircraft-related lightning and icing certification technology development is insufficient, there is need to develop appropriate airworthiness certification guidelines. In this study, after analyzing the laws and regulations related to aircraft by the FAA and the EASA, we tried to incorporate the lightning and icing certification guidelines for the UAM aircraft. We also analyzed the effects of lightning and icing on UAM aircraft using computational simulation, and presented the basis for establishing practical guidelines for the certification of UAM aircraft to be adopted in the future.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.371_372
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• 2009

This paper describes surge characteristics on 345kV combined transmission system mixed overhead line and GIL(Gas Insulated Transmission Line). Then, it is compared with the results of the system mixed overhead line and XLPE power cables. Finally the lightning overvoltages are also discussed according to surge arrester installation in two kinds of combined transmission systems when the lighting strikes on the phase conductor.