The present paper proposes a method for analyzing lightning surge overvoltages at a substation using steady-state solution. A lightning current is assumed to be periodic so that it is represented by Fourier series. Then, the frequency responses of the line and substation impedances seeing from the substation entrance and of the steady-state solution of the open-end line voltage when the substation is deleted are obtained easily. The steady-state voltage at the substation entrance is evaluated from the above frequency responses applying Thevenen's theorem. The transient voltage is given as the sum of Fourier series of the steady-state voltage. The calculated results of lightning surge overvoltages by the proposed method agree reasonably with the transient solutions calculated by the EMTP, and the computation time and memory are far smaller.
For the proposed method evaluates a lightning surge overvoltage only by a steady-state solution, the method has an advantage to be able to estimate easily the effect of circuit parameters of a substation applying an alternating current theory. Therefore, the method might be quite useful to study the relation between bus length and an overvoltage generated, estimation of an optimum position of arrester installation, and so on.

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Mono- or multi-pole towers are sometimes adopted instead of traditional lattice towers, in order to minimize the environmental impact of power transmission lines. The pole-type tower is expected to have the larger surge impedance than a lattice tower because the former has a smaller average diameter than the latter. This paper investigates experimentally the lightning surge performances of the pole-type tower models of various geometry. Then the empirical formulas of surge impedance are derived for the mono- and multi-pole towers as a function of their geometries: the height and the radius of the pole and the distance between two neighboring poles. The equivalent pole radius is derived and given by the function of the radius at the top and the bottom of the pole. The equivalent pole distance is also derived and given by the function of the distance between two neighboring poles at the tower top and the tower base.

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(1) As the LLP System calculated the current to be 2.3 times that of the true current, we adjusted it correctly.
(2) We graphed the cumulative frequency distributions curves of lightning current amplitudes for each season and polarity. The curves for negative polarity resemble a logarithmic normal distribution curve, but the curves for positive polarity don't. The current values of 50% are similar to the observed datas in Niigata.
(3) When we changed the criteria of electromagnetic field waveform of Cloud-to-Ground (CG) lightning in winter, we were able to improve the detection efficiency of the system from 40% to 70%. We found that the electromagnetic field waveforms of lightning to high structures are different from the ones of CG lightning. And before we changed the criteria, the detection efficiency in summer lightning was more than 70%.
(4) We made the detection efficiency curves for each distance and from the curves constructed lightning frequency level maps.

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Recently, the simultaneous fault of two lines by winter lightning on the coast of the Japan sea and the damage of ground wire become new serious problems. The observation of lightning current is important primary step to solve these problems.
By the way, it was necessary to use large-scale equipments such as commercial power source and shed for usual observation of lightning.
So we have developed “lightning wave memory” composed of Rogowski coil, digital memory and data storage device.
This device is light and can be easily installed on the transmission tower or the ground wire, so we can use it in any observation places.
Moreover, 40 lightning current waveforms with the time, peak current, porality and energy are memorized automatically by it.
Many lightning current waveforms were already obtained by this divice.
In this paper we deal with the structure of a developed lightning wave memory and the observation results by using this device.

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Simultaneous observations of the electric field intensity on the ground as well as optical observations of lightning flashes by VTR cameras have been performed in each one month from November to December for these five years in Kahoku-gata, a reclaimed flat land territory (4×5km in E-W and N-S directions) located in the northern suburbs of Kanazawa in winter. Polarity and approximate intensity of the electric field intensity on the ground have been obtained from continuous observation of the point corona discharge current. Regional distribution of the electric field is presumed by a graphical method on the basis of the time variations of those two quantities observed at six sites in the territory. On the other hand, lightning discharges occurred in the same territory have been recorded by several VTR cameras from two directions, three cameras observing from the east at Ishikawa College of Technology, other two from the north at Unoke fire department. These cameras were continuously operated for eight hours when thundercloud is forecasted to come over there.
Finally, the eleven accurate stroke points of the cloud-to-ground discharges were determined on the map. And it is found that the eleven stroke points are all located within the narrow band of ±1 km width including the boundary line between the positive and the negative domains of the electric field on the ground.

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The experiment of rocket-triggered lightning has succeeded to guide a lightning to a test power transmission line tower in 1986. By this success, it became possible to measure the lightning current flowing through the ground wire and each leg of tower simultaneously, and also to study the shield to the lightning stroke to the line. In the triggered lightning experiment to the line or tower, it is needed to measure the lightning current at the discharge stroke channel in air directly by the current measuring device carried by a small rocket. For the purpose, a new method using the magnetizing effect of magnetic tape by the lightning current was developed as a small and light device carried by the rocket.
In this paper, the characteristics and accuracy of the device are described with the measured results in the triggered lightning experiment to the test power transmission line in comparison with the results measured by Rogowski coil.

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A new tower model for lightning surge analysis is developed. A field test result of a tower surge characteristic is transformed into the frequency domain by numerical Laplace transform, and the frequency response of the tower is obtained. The propagation constant of the tower including the frequency-dependent effect is obtained from the frequency response.
Thus, the tower is represented by an ordinary distributed-parameter line including the frequency-dependent effect of the tower impedance, i. e. the traveling wave deformation of the tower.

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It is widely known that the measurements of an electrostatic component under a thunder cloud are useful for forecasting lightning discharges.
The measurement has been performed so far with the use of a fieldmill in the market. However, there are many problems in this; for example, weak time resolution, low sensitivity and many restrictions in the observation circumstances.
We have proposed a pair of doughnut shaped static antennas (denoted as a static antenna) for measuring the electrostatic component of the lightning discharges. But, we have not identified that the received signals through the static antenna really show the electrostatic component.
In the present paper we will clarify that the electrostatic component is measured correctly by the static antenna, after comparing the distance dependence of the electrostatic field and the radiation field component which is received with a CIGRE antenna. We have also confirmed this fact by observing the ratio of the output amplitude of the doughnut antenna to that of the fieldmill as a function of the distance between the struck points of the lightning discharges and the observation site.
The sensitivity of the present antenna is calibrated by using the fieldmill. It is revealed that the static antenna has many advantages in the measurements of a static field component in any weather conditions.

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A lightning strength parameter, α, (denoted as LSP or LAIDO) which is used for characterizing the phenomena of lightning activity has been proposed, where, α is defined by the characteristic energy obtained from the distribution function of a radiation field component, E_r, in the electric field changes produced by lightning discharges. Here, that the energy distribution of E_r, component has Maxwellian type has been observed.
In order to proof more clearly the abovementioned assumption from the other point of view a change of amplitude of the electrostatic field component, E_s, has been measured to make distribution functions.
In the cloud-to-ground lightning discharges, E_s component has been observed to show positive sign in the changes, but in the inner-cloud discharges it shows either negative or positive change depending on the distance between the striking point and the observation site. Therefore, it is necessary to sum up the number of occurrences of both positive and negative components for making a energy distribution of E_s, component.
When the change of the E_s component has been measured, both a fieldmill and a pair of doughnut shaped static antenna are employed. It is shown as a result that the change of the amplitude of E_s, component has a Maxwellian type energy distribution. Then, we have defined a characteristic energy β obtained from the electrostatic component as also a measure of LSP.
After comparing α with β, it is clarified that the β has the same characteristic nature with α, and the lightning activity could be estimated from β.

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Surge arresters are usually installed in a substation to reduce crest of surge voltage below insulation levels of electric power equipments. Nevertheless, it has been reported that the harmful overvoltage might be induced by local resonance in a transformer winding.
Waveftorms of the surges coming over a substation transformer due to flashover at different transmission towers are calculated by using of digital computer program of the EMTP (model-39). The derived incoming surges are all represented as being oscillatory due to reflections between the flashover arc at the striking point and the transformer. When the lightning striking point is a few km far from the substation, the incoming surge oscillates with some tens of kHz and it might cause a harmful resonant overvoltage in the transformer windings. Thus, this kind of lightning stroke is emphasized in this paper as referred to SLS: short-line lightning stroke. It is pointed out that the lightning arresters installed on the transmission towers is so much effective to prevent an oscillatory incoming surge from occurring.

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Recentry, according to the trend that utilization of electricity expands to wider area, effects of outages by lightning on transmission lines become a problem and the cost of electricity transmission tends to go up by anti-lightning measures. This presents growing necessity of more reasonable design of transmission lines. To realize reasonable insulation design, it is necessary to know accurate regional distribution of the lightning incidence. So far, very few were reported as to the regional distribution of trip-out rates of transmission lines.
This paper describes the regional distribution of the lightning trip-out rates of transmission lines in CHUBU AREA. The degree of the lightning trip-out rate of transmission lines in a certain sub area is proposed to be expressed by two indexes. The ground flash density of lightning is also given from these indexes.
Newly introduced Indexes are as follows, lightning trip-out index, A_i, which is given by dividing trip-out rate in a certain sub area by the trip-out rate in whole CHUBU AREA.
Total index, A₀, is given by modifying A_i by taking the line length into account.
Total index (A₀) shows good correlation with counts of CIGRE lightning flash counters, but it shows very poor correlation with IKL values.
The ground flash density of lightning (N-value) is also given from these indexes. These indexes would be effective to achieve resonable design of transmission lines.

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The leader and return stroke channels are represented by co-axial cylindrical electrodes with a short circuit. When negative DC voltage over an onset corona voltage is applied to an inner electrode, negative space charges caused by corona discharges from the inner electrode are formed between electrodes. As the inner electrode is grounded by a chopping gap, many impulsive discharges occurred around the inner electrode for over 100μs. The number of the dischargesincreases in keeping with the applied voltage. The corona sheath current flowed to the ground is calculated from light intensity changes obtained here. This current waveform is very similar to that calculated by the Lin-Uman-Standler return stroke model.

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Characteristics of lightning flashes with multiple strikes to the ground within 1s are investigated, based on the data of video pictures of lightning channels and the electric field changes. In winter, the occurrence frequency of lightning flashs with multiple strikes to the ground is 55% which is roughly twice as large as that in summer. The number of strike points in winter is also larger than that in summer. The largest number of strike points is 17 in winter, whereas 4 in summer. The polyphase fault on a power transmission line in winter might be caused by a lightning flash of this type. The average time intervals between strokes are less than 17 ms (one TV field) in winter and 90ms in summer respectively. The average distance between strike points are 1.3km in winter and 1.9km in summer.

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Surge propagation chracteristic of cables fixed to a transmission line tower is not studied well, in comparison with the case of the tower itself. This paper studies characteristics of the surge propagating between the cable and the tower based on experiments with a step pulse voltage injection to 77kV XLPE cables fixed to a mean scale tower. We also investigated to the possibility to regard the tower as the ground in EMTP calculation for simulating those experiments. As a result of the test, we have found that aluminum cleats caused a significant influluence to the character of the surge propagation between the cable sheath and the tower. Aluminum cleats fixing cables to the tower makes the apparent speed of the surge to be delayed. Moreover calculation techniques were developed to get more accurate values of surge impedance and velocity, when we considered about the cable with wire stranded shielding in EMTP simulation. This paper describes details of experiments and the mechanism of cleats' influence using numerical simulations by the EMTP.

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In the last decade, increasing attention has been paid to ELF (Extremely Low Frequency) electromagnetic environments in work areas as well as in and near homes, regarding their interaction both with electric apparatus such as CRT's and with biological systems. This contribution presents experimental and theoretical analysis of 60Hz magnetic field (B-field) characteristics at and near ground level in both 187/66kV EHV and 66/6.6kV HV power substations. Experimental results of B-filed profiles along horizontal paths as well as harmonic contents in B-field waveforms at several positions are shown and discussed. Furthermore, analytical B-field profiles calculated by using a B-field approximation method based on Biot-Savart law are shown and compared with the measured ones. The comparisons verify that the assumptions employed are applicable to the substation B-field calculation, and that the B-field calculation method employed can estimate the B-field in EHV and HV power substations to significant accuracy, except for areas where localized B-field sources such as power transformers and underground power cables exist. The analytical profiles of three orthogonal components of the B-field are also described in terms of equi-flux contour maps, which show 3-dimensional characteristics of the B-field in power substations.

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For construction of low-voltage power distribution systems, it is important to have correct informations on the probability of failures by the lightning in order to meet the requirement for high reliability of these systems.
The burn-out of low-voltage distribution equipment is triggered by flashover due to the lightning overvoltage, which is followed by the arc discharge current at the commercial frequency voltage. The arc characteristics were investigated by superimposing the lightning impulse voltage across terminals of the low-voltage distribution equipment connected to the commercial frequency power supply in order to reproduce these events on an experimental basis. As a result, it was found that the arc characteristics were affected by a number of factors.
The probability of flashover occurence on low-voltage distribution equipment is determined based on the frequency distribution data of lightning overvoltage occurence obtained by the surge counters monitoring on actual distribution lines. Then, the probability distribution of arc currents is established by application of the above experimental equation on arc characteristics. Finally, the method for evaluation of damages by the lightning to low-voltage distribution equipment on actual lines was investigated with the frequency of lightning strokes and the configuration of low-voltage distribution systems taken into consideration.

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Many knowledge-based expert systems have been developed. And their reliability is becoming a major bottle-neck for their practical use. This paper proposes a dynamic verification method for knowledge-based systems to detect their errors automatically. This is such a method that makes knowledge-based system to be verified infer actually and keep a good watch over their reasoning process.
To detect systems errors, the verifier “Correctness Checker” traces the reasoning process by watching their working memory, which is a storehouse of reasoning data and therefore can be considered to reflect the systems inference exactly. And we adopt the system specification in the form of constraints as evaluation criteria. We consider that there should be any error in the system if its working memory is changed to violate their constraints.
In this paper, we describe (1) static logical verification method for rule-based systems and its limitations, (2) new framework of dynamic verification method and evaluation criteria, and (3) execution example of dynamic verification for an operation decision-making system for electric power supply systems.
This dynamic verification method has the following advances: (1) Verification for a whole inference system is possible. (2) We can certify what items verified systems satisfy explicitly. (3) The Correctness Checker is a module completely independent of knowledge-based systems to be verified.

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