Voltage distortion of 6.6 kV distribution systems has been increasing recently especially in commercial areas. Harmonic currents of certain orders are amplified and voltage distortions are genarated by the resonance between system impedance and static capacitor under the leading power factor condition.
This paper describes the results of the test on suppression effects on model systems and an actual system. The effect of the use of an active power filter on the resonant harmonics of the system including capacitor was verified.

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This paper presents a new phase frame modelling using recursive convolution for the transient analysis of unbalanced transmission lines. The recursive convolution are formed from the first and second order transfer functions derived via an approximation method for the frequency dependent characteristics of the phase frame attenuation and surge admittance. The accuracy of the approximation is considerably high. Then the model is free from the contradiction to the physical causal relationship observed in the frequency dependent modal transformation matrix used by the modal frame model with full representation of frequency dependence of unbalanced transmission lines. The resemblance of wave forms between simulation and field test results are good.

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This paper presents a peak load forecasting system using multi layer neural networks and fuzzy theory. Electric load forecasting in power systems is very important task for it's reliability and economic operation. Especially daily peak load forecasting is one of the basic operation of generation scheduling for the following day. Therefore, many statistical methods have been developed and used for such forecasting. Although, it has been difficult to construct a proper functional model, or needed huge effort.
The system we developed is applied by neural network and fuzzy theory to forecast for daily, weekly and monthly peak load . The system consists of an engineering workstation(EWS) and a personal computer(PC). EWS is for learning and data-bases, PC for man-machine interface such as forecasting operation.
The system has used under actual task since june '93. The result evaluated by absolute mean error is 1.63% for 10 months. From the results shown here, the system applied by neural network and fuzzy theory has high validity.

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This paper describes a new method of the tracing technique of closed spatial curves relating to find multi set of solutions for load flow studies in higher precision. Numbers of 2n curves are defined in voltage coordinate system for a single set of load flow solution of the model network with n+1 nodes. Each closed curve involves two set of point which satisfies the set of load flow equations. Proposed curve tracing algorithm contains definition of starting point from a given solution, calculation of derivatives for coefficients of Taylor's series up to third order approxi-mation. estimation of a new point of distance ds from old one, correction of tracing error caused by truncation of Taylor's expansion and finding the separate set of load flow solution after several times of repetitions. The results show that 136 set of solution are obtained for Klos & Kerner's light loading model system, and that the method is more effective than others.

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A static Var compensator (SVC) can improve the steady-state stability (or the small signal stability), if it is located appropriately. The present paper proposes a method for selecting the best siting of SVC in large scale power systems for damping effectively.
Conventionally, it is thought that SVC improves steady-state stability by its voltage regulating ability. From this point of view, the stability can be improved significantly if SVC is located at the bus which has a large voltage fluctuation due to the lightly-damped power swing mode. In contrast to the conventional viewpoint, the present paper makes it clear that the steady-state stability deteriorates by the conventional voltage regulating control of SVC in some cases. Therefore, the voltage fluctuation is not appropriate index for effective damping.
The present paper explains the mechanism of improvement of steady-state stability by SVC in terms of the modal analysis. On the basis of the modal analysis, an index for determining the location of SVC is derived. The index is called LIED (Location Index for Effective Damping) by the authors. Digital simula-tions are conducted for an 8-machine longitudinal system and a 29-machine looped system to demonstrate the validity of the proposed index.

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Photovoltaics (PV) is considered as one of the most expected renewable energy sources to be developed more economically and superconducting magnetic energy storage(SMES) is also expected to be put into power grid in the near future.
To get a reliable and easily controlled power source using PV, the hybrid system with SMES is desired because of the high efficiency, reliability and quick response characteristics of SMES as a power storage equipment.
In this paper, we propose a conceptional configuration and operating algorithm of PV-SMES system on the assumption that it would be connected to the power grid for commercial use. Considering the load leveling function of PV-SMES system, an optimum daily operation scheduling method of power systems which includes unit commitment and economic load dispatch is presented. The various features of PV-SMES system, such as, load leveling, operating cost reduction effect, smoothing effect of PV output, etc., are demonstrated and confirmed through simulation results for a model power system.

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Various preventive measures are taken against lightning faults in power transmission facilities to decrease their occurrence frequency and improve transmission reliability. However, how much they enhance the power carrying capability of a transmission line has not been quantitatively defined so far. To solve this issue rationally, it is useless to adopt the conventional deterministic approach which is widely used in power utilities as a general rule for power system planning.
This paper proposes a new method for numerical evaluation of the transfer capability by means of lightning measures. The proposed method is based on a probabilistic approach in which several fault patterns are considered with their occurrence frequency and maximum transferable power. This paper also applys the developed method to a trunk transmission model system and shows numerically the effect of 3 ground wires on the increase of carrying capability of a 500 kV transmission line.

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This paper describes the results of an investigation of the electric field-induced motion in mineral oils between stainless steel electrodes after change of electrode polarity.
We have observed time dependence of current and schlieren images of the motion by using mineral oils of electric conductivity ranging from 4.5×10^-14S/m to 1.7×10^-12 S/m at the charging voltage equal to ±8kV and by charging voltage ranging from ±1kV to ±10kV at the conductivity equal to 9.0×10^-14S/m. The results are as follows: (1) An increase time of current and a time of peak current shorten with the increase of electric conductivity and electric field intensity. (2) The motion occurs with a time delay after change of electrode polarity and produces a peaked behavior in the current waveform. (3) These time are inversely proportional to the electric field intensity and the quantity of charge carriers drifting between electrodes from the increase time of current to the time of peak current. (4) The experimental results are well explained by established model.

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For complex and large scale power systems, it is very important to efficiently carry out dynamic stability analyses. The QR method, which is able to obtain all eigenvalues with enough accuracy, cannot unfortunately be a useful tool for large scale power systems due to the large amount of storage and inhibitively long computation time. Moreover, only dominant eigenvalues corresponding to poorly damped oscillation modes are needed in actual dynamic stability analyses. Although several methods of selectively obtaining a desired set of eigenvalues have been proposed so far, they are not fully satisfactory and they need further refinements.
This paper presents an efficient algorithm based on the simultaneous iteration method (SI method) that can selectively compute the dominant eigenvalues with less execution time. The proposed algorithm has made several improvements over the original SI method, thus realizing faster calculations and ease of use. The algorithm has been successfully applied to the IEEE118 node test system with 54 units.

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When a photovoltaic power generation system is to be connected with a low voltage distribution line, it is necessary to install an insulated transformer or interrupt the operation of an inverter by detecting the direct current leaking from the inverter, in order to prevent the occurrence of asymmetrical excitation of a distribution pole transformer due to the flow of direct current into it.
In this paper, the phenomenon of asymmetrical excitation of a distribution pole transformer due to direct current inflows was studied both experimentally and through a theoretical simulation, in order to clarify the detection level of the direct current in question. Test results showed that the excitation current increases in proportion to the direct current, and that the smaller the transformer capacity, the larger the ratio of the excitation current to the rated load current. These findings agreed with the results of the theoretical simulation.

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In closed cycle MHD power generation, the realization of uniform plasma in whole channel is needed in order to achieve high generator performance. The disk generator used in experiments should have the wide allowable operation range as well as the high maximum enthalpy extraction ratio, for the purpose of the successful power generation experiments. Therefore, the stability of operation of disk MHD generators driven by cesium seeded argon working gas is investigated by means of the linear and nonlinear theories of ionization instability. For the experimental generator whose height changes straightly along the disk radius, such as disk type generators installed in FUJI-1 facility, too large area ratio of outlet to inlet makes the region of acceptable operation conditions narrow. The near-ideal experimental generator which have the wide region of operation conditions providing high enthalpy extraction ratio is proposed by modifying the channel shape of a disk generator installed in FUJI-1 facility. It is found from the discussions of enthalpy extraction ratio of the proposed generator that the electron temperature at the inlet must be kept around 5000K.

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The performance of non-equilibrium MHD disk generator with segmented loads is examined with γ-θ two dimensional numerical simulations. The use of segmented loads is found to improve the generator performance when a low electron temperature plasma is introduced to the channel. The simulation results reveal the desired values of load resistances connected in upstream and downstream regions, respectively. The concept of the segmented loads is considered to be superior to rearranging seed fractions and load resistances.

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In overhead distribution lines, outages due to trees, animals, etc. in contact with covered conductors have become one of the serious problems in the recent years. Especially, the outage due to bird nests is severe. From the observa-tions of the bird nests in the actual overhead distribution lines, it is guessed that the outage follows a leak through the nest material which approaches to an energized equipment under rainy condition. On the other hand, it is pointed out that the outage may also follow a surface flashover on the covered conductor between the nest material and the energized equipment when a lightning surge whose peak value is lower than the operation voltage of an arrester appears. Thus, the way how the outage occurs is not clarified in detail. In this study, the surface flashover was observed in a laboratory test in spite of the installation of the arrester. The flashover occurred on the covered conductor which had a knife trace damage passed through the conductor jacket when a tie wire was grounded and a lightning impulse voltage was applied. Then, the surface flashover voltages were measured for the various damaged position. Furthermore, the effects of wet and the shape of damage on the flashover voltage were examined. From the results, the occurrence of the outage accompanied with the surface flashover was discussed.

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The correlations between fluctuations of the flow and those of the electromagnetic fields in a partially ionized plasma were numerically investigated. The currents due to prescribed flow field fluctuations were calculated by the generalized Ohm's law. The time-averaged flow fields were assumed to obey the 1/7-th power law. Intensities of the velocity and temperature fluctuations were given as functions of the distance from the solid wall of the duct. The Reynolds' stresses and the turbulent heat fluxes were also taken into account in evaluating fluctuations of velocity and temperature. Conventional methods ignore these factors in calculating the correlation of electromagnetic fluctuations with.those of flow fields. This paper has shown that such a conventional method is valid only for the time-averaged electrical quantities of the plasma. It has also been shown that the externally-applied nonuniform magnetic field, known as the shaped B-field configuration (SFC), is effective in suppressing the Joule dissipation in the presentce of these fluctuations.

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