Characteristics of mesospheric sprites in the Hokuriku area and their causative lightning discharges

Mesospheric optical phenomena (including sprites) are becoming an interesting subject from the standpoint of atmosphere–ionosphere coupling. This paper deals with our observation of sprites associated with winter thunderstorms in the Hokuriku area and we show the characteristics of those sprites and their parent lightning discharges. Although the scale of Japanese lightning in winter is very small compared with the MCS (Mesoscale Convective System) for the summer continental lightning, the essential quantities (polarity, charge transfer, and so on) are found to be nearly the same as those for the MCS. However, an additional factor might be required, such as the self‐organization of the lightning. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 153(3): 9–17, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20178     

Achievements of recent research on electrical discharges and theirpractical applications in Japan

In recent years, many of the researchers in the field of the discharge-aided environment improvement technology have been published, and it is expected that such a tendency will be continued for a considerable length of time in the future, and many fruitful outcomes are anticipated. It has conventionally been believed that that the understanding of the uses of discharge phenomena has mostly been due to experimental discovery, but in the future there will be accumulation of knowledge by the study of the collision process of electrons, atoms, and molecules. This latter approach has been vigorously promoted in Japan with practical use in mind     

雷击建筑物时的雷电流分布研究

建立了雷电流、雷电防护系统、配电变压器等配电网络的模型，利用国际通用的电磁暂态分析程序EMTP研究了TT系统（一种典型的低压与电系统）在遭受雷击时，雷电流在TT系统中的分布。并研究了单相和三相供电、不同波形的雷电流、传输线的线路阻抗对雷电流分布的影响。     

Study on the effectiveness of lightning rod tips in capturing lightning leaders

This paper addresses the performance of various lightning rod tips: pointed, concave, blunt, flat and conical for lightning air terminal (LAT). To observe the behaviour of the various lightning rod tips, laboratory examination was conducted under two conditions, i.e. corona emission pattern under quasi-static electric field and lightning impulse testing—with and without pre-ionization. The data obtained from the corona emissions were correlated to the surface sharpness area of the tip. Using dimensional analysis, it can be concluded there is strong evidence that increased surface sharpness can lead to an increase in the corona discharge current. In addition, an impulse test was conducted to determine the performance of the LATs with different tip types and sizes. Using the individual and competitive test, it was found that the blunt LAT is the most recommended receptor.     

Quantification of the probability of lightning strikes to structures using a fractal approach

Recently fractal theory has been used to model the observed paths of lightning discharges. This paper extends previous work by using a fractal approach to describe the effects of tortuosity and branching of the lightning channel. In particular, we use the model to make predictions of the probability of lightning strikes to practical structures. Some of the specific estimates include the probability of strikes as a function of interception angle, predictions of the strike points on structures, and the probability of "side strikes" to tall structures. Significant polarity and geometric effects are shown. The shielding effects of nearby taller structures, shielding failure or "breakthrough" probabilities of so-called protected objects, and the effects of ground topography are also examined. The results are discussed in terms of the implications for the protection of structures against lightning.     

海南强雷区典型配电线路差异化防雷措施研究

海南地处我国最南端,雷电活动极为强烈,绝缘水平较低的10kV配电线路极易因雷击跳闸,直接影响海南工农业生产生活用电.因此,有效提高10kV配电线路防雷性能评估水平与治理能力,对保证海南地区供电的稳定可靠十分重要.本文采用配电网差异化防雷技术开展海南强雷区10kV配电线路防雷综合治理研究,首先建立综合考虑雷电信息、线路结...     

Phenomenon of skipping sparks in discharges on a dielectric surface

Gliding sparks are associated with channel breakdown in air near a corona precharged dielectric layer backed by ground. Characterized by high current, their bright channels usually end in sudden branching/dimming. Infrequently, there occur cases in which channel brightness is interrupted, with no evident local branching but a new leader continuing on propagating after momentary delay. This skipping-spark phenomenon has been studied in an experimental system intended for taking Kirlian photographs. Operated in a Lichtenberg-figure mode, the method yields evidence in some detail. The authors report on observations of spark-channel touchdown and subsequent rebounding. A model based on nonuniform surface charging is proposed for explanation     

串联供气电池组性能研究

提高自增湿质子交换膜燃料电池水管理能力的关键在于电池组结构设计。采用反应气串联供给的电池组结构,且反应气经循环回路进入电池组进行再利用。实验结果表明:氢气循环对电池组内水分的均匀分布有一定的促进作用,氧气循环操作对电池组性能影响明显。     

Analysis of the response to a lightning strike of a towers cascade equipped with its grounding systems

This paper presents an analysis of the response to a direct and indirect lightning strike of a transmission line towers cascade using a direct time domain approach based on the corresponding transmission lines equations and finite difference time domain (FDTD) method. The proposed work deals with a real case of towers being connected by ground wires and equipped with grounding systems with different topologies (vertical or horizontal conductor buried in the ground). In particular, this work realistically represents the tower geometry and accounts for the propagation phenomena along the tower and between the towers. The analysis carried out in time domain deals with rather complex electrical devices (towers, ground wires and grounding systems), but at the same time requires very low computational cost and also provides relatively simple implementation. Some illustrative computational examples related to some engineering applications are given in the paper.     

220 kV同塔多回线路防雷措施探讨

介绍了上海地区历年来220 kV输电线路雷击跳闸情况,通过对同塔多回线路的雷击跳闸统计分析与防雷验算,探索了220 kV同塔多回线路防雷措施.     

The effect of neutral earthing practices on lightning currentdispersion in a low-voltage installation

Computer modeling with the EMTP code has been applied to several configurations and earthing practices in use in various countries to show the effect of any differences in the dispersion (sharing) of a lightning stroke current among the available paths for the earth-seeking lightning current. Simplifying assumptions have been made to some details of the configurations to focus on the main difference-earthing practices. Identifying such differences provides the necessary perspective on their significance and the strong need to take them into consideration when developing international standards on surge-protective device applications     

Contribution of surface conductivity to the current forms of partial discharges in voids

The current form of partial discharge (PD) in a void was divided into fast and slow components, with short and long fall times, respectively. Comparing these with the current shape of PD in a void between two metal surfaces, in which the slow component was not observed, it was suggested that the formation of fast component in a usual void was due to the instantaneous discharge between the discharge areas of the PD, i.e. the region to which the carriers in a PD process can instantaneously propagate, and the slow one might be due to the low conductivity in the regions outside the discharge areas. An equivalent circuit was proposed to describe the effect and numerical simulations were carried out. It was suggested that the fall part of the first PD after polarity reversal might reflect the surface conductivity change in aging process.     

Improvements of an FDTD-based surge simulation code and its application to the lightning overvoltage calculation of a transmission tower

This paper presents new features recently added to a general-purpose surge simulation code based on the Finite Difference Time Domain (FDTD) method. The added features include various-shape conductor models, lumped-parameter circuit-element models, a lightning-channel model, and an integrated analysis environment (IAE). For precisely modelling the shapes of various conductors, the following conductor models have been added: inclined thin wire; disc; square plate; cylinder; cone; and quadrangular pyramid. The lumped-parameter circuit-element models allow the user to represent the lumped impedance of an apparatus placed inside the analysis space. The lightning-channel model realizes a return-stroke development at a speed slower than the light speed. The IAE includes a Graphical User Interface (GUI), which allows the user to enter geometrical data in a visual way. It also provides a waveform plotting program for viewing voltage, current, electric-field, and magnetic-field waveforms and a movie program for displaying the animation of a transient electric/magnetic field intensity distribution. For an illustrative example, the lightning overvoltage calculation of a transmission tower is presented.     

Effect of mechanical vibration on the behavior of partial discharges in generator windings

As mechanical vibration usually exists in HV motors and generators, its influence on the partial discharge (PD) needs to be studied so as to improve the reliability of on-line PD monitoring method. In this report, the mechanical vibration frequency was synchronized to the power frequency and the effects of vibration phase and frequency were investigated. Because the length of the discharge gap changed with the vibration, obvious variation in the slot-PD patterns was observed at different vibration lead phase and frequency. Moreover, when the vibration amplitude was large, it was also found that the PD behavior at low voltage just above the PD inception voltage was different from that at higher voltage. This was explained in terms of the effects of the field variation in the gap due to the vibration and the charges left on the insulating surface due to PD.     

Aerodynamic improvement of the assembly through which gas conduits are taken into a smoke stack by simulating gas flow on a computer

Results from computer simulation of gas flow motion for gas conduits taken on one and two sides into the gas-removal shaft of a smoke stack with a constant cross section carried out using the SolidWorks and FlowVision application software packages are presented.     

Optimisation of a sensor for onsite detection of partial discharges in power transformers by the UHF method

Among the different solutions which allow onsite Partial Discharge measurement in energized power transformers, the UHF technique is gaining general interest. In order to apply this method in existing transformers, it is considered advantageous to design a UHF sensor to be fitted inside the transformer tank. This paper describes the constraints affecting the development of such sensor and the process followed to optimize its design. During this process, different solutions for broadband UHF antennas were analysed. The selection was based on computer simulation and experimental results. Computer simulation was used to evaluate differences in radiation pattern, antenna impedance, gain and effective area. Measurements of the antenna response to different partial discharge sources in oil were performed using an oil dielectric breakdown test set in an electromagnetic shielded laboratory. A group of selected antennas were then tested in a power transformer simulating the broadband signals generated by partial discharges by injecting controlled voltage pulses in the transformer. Finally, a sensor based on a conical monopole antenna structure was built and attached to a specially designed housing to be fitted inside the transformer tank through the drain valve. This final prototype was benchmarked during a high voltage factory test of a power transformer which showed a significant partial discharge activity.     

高阻尼高抗冲聚苯乙烯解决空调蜗舌异响的研究

空调挂机蜗舌是开机制热时温度变化最大且短时间温差最大的区域,蜗舌受热膨胀使得卡扣等装配部位产生形变位移,而形变释放瞬间部件会产生振动发声.为解决该问题,采用高阻尼的高抗冲聚苯乙烯(high impact polystyrene,HIPS)材料进行异响和振动振幅频谱测试,结果发现高阻尼、低尺寸变化率的HIPS材料可大幅减...     

A study of the effect of earthwire materials on lightning induced voltages and currents in transmission lines

Two materials commonly used for overhead static conductors are compared for their response to voltages and currents induced in a transmission line by a lightning stroke in the proximity. Mean characteristics of initial and subsequent strokes form the basis of the necessary field calculations. Frequency domain solution techniques are used to compute the total field, considering both the lightning source field and the reaction field of the induced currents.The results indicate only slight differences in the voltages induced in lines using either aluminum or steel overhead earthwires. However, the magnitudes of induced currents are very sensitive to the type of earthwire material.