The lightning outage rate is one of the most important factors to design transmission lines. it is very complicated to calculate the lightning outage rate because there are many parameters to be considered such as a lower-footing resistance, a peak value and a waveform of lightning current, a striking angle and so on. The double-circuit outage is the most urgent problem in electric power systems. However, it is difficult to analyze a multiphase flashover of the transmission lines because the flashover on each phase occurs sequentially and the arcing-horn voltage is affected by the other phase flashovers, An analysis using the EMTP shows a sufficient accuracy, but requires a large computation time. Thus, a more convenient and simplified method is desired to estimate the flashover for the parameters.
This paper proposes a calculation method to evaluate a back-flashover outage due to a direct-lightning hit t a tower. The method is based on an integration method and a lumped-parameter circuit theory. The method not only treats an arcing-horn voltage and a flashover time, but also is able to handle nonlinear characteristics such as a nonlinear grounding resistance and the multiphase flashover. Thus, the proposed method is very convenient to investigate a lightning performance.

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This paper presents experimental results of lightning current characteristics of a 500kV transmission tower footing base with various grounding electrodes using a 3000kV impulse generator. Further, general prediction curves for the lightning performance of the grounding electrodes under various soil resistivity are compared with the experimental results. The impulse tests on them were carried out with currents up to 30kA. The tests under such a large current have not been achieved before, therefore the results of these tests provide a lot of significant knowledge about current dependent characteristics of various grounding electrodes as well as a tower footing base, such that the reduction of tower footing resistances can not be expected under the soil of low resistivity which is below 1000Ωm, and the effect of various grounding electrodes connecting to the tower base for high impulse currents can not function well, mainly due to the interference between the tower base and various grounding electrodes. The critical soil ionization gradient, however, is obtained by alternative impulse tests using a driven hemispherical and rod electrode in uniform soils. Then general prediction curves based on Korsuntcev's idea are derived. The availability of the curve is confirmed by comparison with the experimental results, and the possibility of predicting the lightning performance of tower footing base under the soil of higher resistivity is discussed.

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A field test was carried out to investigate a fault clearing transient due to current interruption of a 3-phase to ground fault at the secondary side of a 3MVA, 22/6.6kV transformer by a vacuum circuit breaker. EMTP simulations in comparison with the measured results have made it clear that the capacitance C_p of a CR divider to measure voltages reduce dv/dt of a transient recovery voltage across the circuit breaker by the ratio of C₁ / (C₁ + C_p) where C₁ the transformer stray capacitance. The leakage inductance evaluated from the transformer rating has been found noticeably greater than that determined from the measured fault current possibly due to the transformer saturation. Considering a transformer magnetizing conductance and selecting an appropriate interrupted-current, an EMTP simulation gives a satisfactory result compared with a field test.

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The electromagnetic radiation field generated by a return stroke current has not been taken into account in a conventrt lightning surge analysis for a direct lightning hit to a transmission line tower. The electromagnetic field, however, greatly affects arcing-horn voltage. Then, a calculation method to deal with the radiation field in the EMTP as a lightning-induced-voltage sot was developed by the authors.
The double-circuit outage on EHV transmission lines in Hokuriku district caused by a winter lightning is one of the n important and serious problems in electric power systems. The winter lightning has been observed to make clear the flasht mechanism of the outage. As a result, it is cleared that the winter lightning is quite different from summer one. Tlius, it is expe, that the peculiarity of a winter lightning discharge causes a multiphase flashover. This paper investigates the effect of the radia field on the multiphase flashover, and compares the actual lightning performance of the multiphase flashover on EHV transmis, lines with calculated results.

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Many lightning stroke models of summer lightning have been proposed by various researchers up to this time. In Japan, it has been required to establish a new lightning shielding theory which considers upward leaders in winter lightning on the Japan Sea coast.
Differrences between lightning progression features of winter and summer lightnings prevent the conventional lightning stroke models of summer lightning from application to winter lightning.
Based on lightning observation data and discharge characteristics of long air gaps, a basic model of leader progression was previously proposed by the author. At this time, an improved model (upward leader progression model: ULP model), which considers statistical variation of leader progression, has been developed. This new model can reproduce various lightning features such as distribution of time-to-discharge, the ratio of numbers of lightning stroke to tall structures and so on.
Using the ULP model, shielding performances of high structures such as a lightning shielding tower and an overhead ground wire against winter lightning are predicted and compared with field observations.

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Arresters composed of a series gap and ZnO element have been widely applied for 6kV distribution systems. The purpose of the present paper is to clarify the causes for the changes in the performance characteristics of the arresters operated by surges. The experimental arrester with no spacer is operated by a nominal discharge current under atmospheric air. Then, the impulse discharge and post-discharge phenomena are observed by means of a method connected an image-converter camera to a Schlieren technique.
In the impulse discharge process, a shock wave, the reflected shock waves and the disturbed flow of neutral gases occur in the series model gap. The shock wave can be first observed at the periphery of the luminous channel of arc after the discharge current has risen to the peak value. The disturbed flow occurs even in the weak discharge process which the discharge current was lower and the pronounced light emission from positive column disappeared, and continues for a long time until the end of the post-discharge. It is discussed that how the shock waves and neutral density change influence on the characteristics of the actual arresters for the distribution systems.

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This paper proposes an new Genetic Algorithm(GA) approach for short-term thermal unit commitment. Unit commitment is a complex combinatorial optimization problem which is difficult to solve for large power systems. Up to now, the Lagrangian relaxation(LR) is considered the best way in dealing with large-scale unit commitment although it cannot guarantee the optimal solution. Recently, GA has been successfully applied to combinatorial optimization problem. However, GA is time-consuming since it requires binary encoding and decoding to represent each unit operation state and to compute the fitness function throughout GA procedures. This causes huge computation burden, making it difficult to apply to large-scale system. To realize high speed computation, a new genetic operations such as a few individuals, quick estimation and intelligent mutation operators are introduced. The proposed algorithm has been applied to the large-scale unit commitment problem, and the simulation results show that better solutions are obtained in reasonable computation time.

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This paper presents the experimentally investigated results of a new type current limiter by using a model current limiter. This type of current. limiter consists of a reactor with two coils reversely winded so as to maintain the non-inductive state in the core. A parallel circuit with a power semiconductor switch and a resistor is connected to one of two coils in series. Being maintaining the non-inductive condition by the turning-on the semiconductor switch during the normal loading state, theoretically there is no voltage drop across the limiter, i.e., the impedance of the limiter holds zero. The limiter has a current limiting impedance value during the current limiting performance under a short circuit condition. The principle is that, according to turning-off the semiconductor switch broken the resistor is inserted in the circuit. resultantly the non-inductive condition is canceled. Effects of turn ratios of the reactor windings and characteristics of the inserted resistor with linear and non-linear are experimentally studied. The normal current through a semiconductor is reduced by taking high winding turn ratio of the coil connected to a semiconductor. On the other hand, the voltage across the semiconductor terminals during the current limiting period becomes large as proportion to the winding turn ratio of the coil. The current limiting impedance and energy absorptions to a nonlinear resistors during the current limiting period are numerically analyzed and compared, and the method to determine the optimum windings ratio is successfully proposed.

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Recently, the utility has been able to purchase the electric energy supplied from the Independent Power Producers (IPP) by a de-regulation in the electric industry. This paper evaluates the influence of IPP's uncertainty on utility and/or customer. In general, the production cost of energy supplied from IPPs is lower than that of a utility, however, the IPP's energy has more uncertainty compared with the utility's energy. This paper analyzes the effects caused by IPPs from the following three points: i) By modeling a process of determining purchased power price as a negotiation model, the authors evaluate the influence of its uncertainty on a potentiality to introduce IPPs through variation of the purchased price. ii) The authors evaluate a difference of power system reliability between a system under the de-regulated environment with IPPs and a conventional system without IPPs. It is assumed that the system reliability is determined by minimizing of the sum of supply cost and outage cost. iii) Finally, the authors evaluate that how the customer's various requirement about the reliability influences the introduced amount of IPPs.

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Introduction of higher voltage and larger capacity power transmission lines and the power apparatus has recently changed the electromagnetic environment around them, and thus the precise measurement and analysis become more important. Magnetic field distribution around power transmission line is very complicated because of the three-phase current condition, the three-dimensional configuration of conductors and the existence of ferromagnetic structure, for example. Moreover, little attempt has been ever tried to measure the power-line current and the magnetic field distribution, thus, the effect of unbalanced current, harmonic content have not been fully understood.
From these backgrounds, we simultaneously measured the magnetic field distribution and the current of power lines. It was clarified that the unbalanced current produced the unbalanced distribution of magnetic field and, in this paper, the contribution was quantitatively analyzed.

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High field is very favorable for magnetically confined fusion devices such as a tokamak, but electromagnetic force derived from the field becomes a fatal problem. Especially, the largest in-plane centering force hinders toroidal field coils from operating at higher fields. Although variable pitch multi-helical coils, we are calling force-balanced coils (FBCs), by which this force is drastically reduced, was proposed for the coil system of tokamak, there had been no tokamak device with FBCs. Therefore, TODOROKI-1, a small tokamak device with FBCs. are manufactured and experiments are started. In this paper, the structure of TODOROKI-1 is indicated, and stray magnetic field and centering force on FBCs are investigated. The plasmas have. been generated in the device and attempts for better plasmas are beginning.

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Performance analysis of the stack is important to improve performance of molten carbonate fuel cell (MCFC). Many single cells and stacks, which were made with different cell design and the electrolytes such as Li/K carbonate and Li/Na carbonate, were tested to develop performance analysis method of stacks. At first, an equation of the cathode reaction resistance was verified using the single cell test results since cathode reaction resistance is the major factor in MCFC performance. Performance analysis method for single cell was applied to stack. However, parameters of the equation, determined by fitting method were not correct since stack data were scattered, Graphical method for determination of the parameters was developed and was confirmed to determine parameters of stacks with accuracy.

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It is necessary for a power system to undertake maintenance works regularly to secure stable power supply, which inevitably cause outage of associated apparatuses. This problem, referred to as the outage planning of an electric power system, has been so far made based on experiences of planning engineers, However, the scheduling made by the engineers has not been necessary optimal since there are no rational criterion to judge the results. Furthermore, this problem belongs to a class of combinatorial optimization problems.
This paper presents a method for outage work scheduling by using hypothesis-based reasoning, The specific features of the proposed method can be summarized as follows: (1) the date and time of outage works is not needed for the scheduling, (2) planning engineers can make use of the knowledge on the combination of outage works, and (3) rescheduling for weather conditions and extra works is made so as to retain the original plan. The proposed method is applied to test cases with 24 merged outage works taken from a part of the 110kV transmission line system.

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The electrical data such as bus voltage, bus and line load flow acquired from a power system does not imply the stability of the system voltage. Accordingly, a proper index is needed to seize it.
This paper proposes a new voltage stability index based on the equilibration force of load which enables the load to operate steadily, using load admittance. The index is composed of the characteristics of load and power system, and expresses ideal state by the value 1, critical state by 0. The index value between these border values represents stability extent, therefore, this index is possible not only to detect the critical state, but also to expresses the degree of stability. The computation of this index is consist of load flow calculations at the conditions of two specified load demands in the vicinity of each other and the index formula. It is more compact than the calculation of other indices formerly proposed.
Owing to above mentioned features, the proposed index would be useful in the field of on-line monitoring, contingency analysis and screening of multiple cases analysis for power system planning and operations.

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In this paper, theoretical consideration is made on possibility of subsynchronous resonance (SSR) in longitudinal power systems. Shunt capacitors are used for reactive power compensation in our country, but series capacitors are not used in general. Possibility of SSR is therefore small. However, if power transmis-sion increases, and accordingly, if shunt compensation increases in amount, there is no guarantee that SSR never occur. First, we investigate network impedance viewed from a generator. Its resonant frequencies get lower with increase in transmission power. One of them gets subsynchronous if the power exceeds a value. In this area, there is some possibility of SSR, which is confirmed with the damping property of the generator. The admittance matrix of the load buses are singular at the resonant frequencies. The number of them is equal to the dimension of the matrix. The frequencies are common to all generators but not limited to one particular generator. One of them gets equal to 60 Hz as we increase transmission power. We regard this power as a limit for SSR. However, steady state stability limit is lower than this limit, and steady operation is not possible at the limit. Therefore, it is impossible to enter the area of SSR. Thus we obtain a conclusion that SSR does not occur in shunt compensated systems. However, this property is easily lost if some series compensation is introduced.

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