Much study to enhance the calculation speed of power system analysis by means of utilizing parallel systems have been proposed. However, the speedup gained in these systems have been small compared to other applications such as circuit simulation mainly due to the smallness of the problem size of power calculations. The before mentioned studies had concentrated on so called “space parallel computing”, therefore parallel implementation grain is small due to the inherent size of power system calculation.
In this paper, we first study the effect that the ratio of data transmission time to calculation time per grain has on the speedup of total calculation. We show that the smaller ratio raises the efficiency of parallel implementation. Lasger grain size of the problem generally yields smaller ratio. Thus, it is shown that attaining a larger grain size is important. In the power system calculation, there is a method called time-domain-parallel computing whose algorithm produces larger grain size. The other application form which results in much larger grain size is multiple cases analysis. We studied the composition methods of these parallel implementations of transient stability analysis using a MIMD distributed memory type parallel processor system.
On a 16 PE system, we attained a speedup of 6.3 in time-domain-parallel computing and a speedup of up to 15.8 in multiple cases parallel analysis. These values are much larger than the speed up in space parallel computing which was less than 2.0

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Stability of a power system is influenced by characteristic of control systems of generators. This paper deals with a single generator operating onto an infinite-bus system with AVR, PSS and GOV. We made a survey of bifurcations in the sample system by computer simulations and presented the bifurcation sets on parameter planes. The parameters are the PSS gain, the transmission line length, specified value of the generator output, and they were widely varied. As a result, we observed loss of stability of a equilibrium point leading to a limit cycle, flip bifurcation and chaos arising through cascade of them, cyclic fold bifurcation, subcritical Hopf bifurcation, and so on. In the case of PSS gain being small value, there was a region where a stable equilibrium point and a stable periodic orbit coexist, and hysteresis was seen in transitions between the two according to variation of a parameter.

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A method of simulation for power system characteristics including a superconducting generator with high response excitation is proposed in this paper. The magnetic energy in the field winding of a superconducting generator (SCG) is much more than that of a conventional generator (CG), because magnetic flux in SCG almost is in air but that in CG almost is in iron core. Then, the power of exciter for SCG at the flux change by AVR is much more than that for CG. Thererfore, the power of exciter must be taken into account for analyses of power systems including SCG with high response excitation. The exciter contains thyristorized converters which generate harmonics currents. The commutations of the thyristors must be taken into account.
By conventional methods of simulation, one simulation code must be made for one power system, and another one for another one.
This paper describes a simulation code flexible for various power systems. In the code, the system is divided into two parts. One is for the field winding circuit and the other is for the power system. They are linked in the magnetic couplings of the transformer of exciter and the magnetic coupling between the armature winding and the field one of SCG. This paper shows the comparison of the simulation results with the experimental one, too

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This paper proposes an optimal fuzzy inference approach to short-term load forecasting. In recent years, artificial neural net based approaches to short-term load forecasting seem to be promising for universal approximation of any nonlinear functions. However, they still have drawbacks that they do not clarify the relationship between input and output variables due to a black-box description, and that they do not necessarily provide satisfactory predicted values due to overfitting and insufficient data normalization. The proposed method constructs an optimal structure of the simplified fuzzy inference that minimizes model errors and the number of the membership functions to grasp nonlinear behavior of power system short-term loads. The optimal model is identified by simulated annealing and the steepest descent method. The advantage of the model allows us to understand the relationship between input and output variables and provide better predicted values. The effectiveness of the proposed approach is demonstrated in examples.

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This paper proposes an efficient algorithm for small signal stability analysis by means of the Arnoldi method with the S-matrix transformation. In the proposed algorithm, the Arnoldi method evaluates several eigenpairs of large scale matrix with less execution time, while the S-matrix transformation makes dominant eigenvalues corresponding to low damped oscillation modes. The combined use of these techniques enables to calculate only critical eigenvalues of large scale power systems efficiently. The Amoldi method has a specific feature that it can obtain eigenvalues successively from the outer part of their distribution. By making use of this characteristic, the spectral transformation can be simplified, thus improving calculation efficiency. The, proposed method is also useful to understand the shape of the spectrum by investigating all of the obtained eigenvalues including non-converged ones. The algorithm has been successfully applied to a large scale power system which has 220 generating units and 3000 state variables.

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Structure of non-equilibrium cesium seeded argon plasma excited with microwave power is simulated numerically. The plasmas produced at suitable microwave powers are found to consist of three regimes, that is, the region limited by charged particle loss toward the wall, the full seed ionization and the diffusion limited regions. The fully ionized seed plasma is produced within the skin-depth determined by the electrical conductivity of the plasma, and the thickness of the fully ionized seed plasma depends on the seed fraction, gas pressure and microwave power.

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The superconducting ac machines such as transformer and reactor are greatly expected to have an important role in the future electric power transport lines. In these machines, superconducting coils are wound by superconducting cables which have low ac loss, stable ac quenching current and high normal resistivity. We have developed Nb-Ti superconducting cables with ultra-fine filament and high resistivity matrix to apply these coils. A cable developed has a structure of double stranded round type using 0.2mm φ strand with 0.14 μm filament and Cu-30wt%Ni as a matrix material. 50Hz quenching current without external magnetic field exceeds 1400Arms. AC loss is 15kW/m3 at the transverse external magnetic field of 0.5T, 50Hz, and normal resistivity is 0.21Ω/m at 0T, 10K.

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The voltage due to lightning surge is now a major problem to be overcome to ensure full reliability of power supply. Hence, gappless oil immersed surge arresters using zinc oxide elements have been applied to pole transformers. These surge arresters are intended as insulation coordination means for pole tranformers. These arresters contribute to the reduction of number of failure of pole tranformers. This paper describes applications and effects of specially developed oil immersed surge arresters in pole tranformers on 6.6kV distribution lines.

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With significant development of power electronics technology, the proliferation of non-linear loads such as static power converters in a range of 50W to 300MW has deteriorated power quality in transmission/distribution systems. Notably, voltage distortion or voltage harmonics may approach or exceed its allowable level in power distribution systems. Individual electric power consumers and end-users are responsible for reducing current harmonics, while electric power companies or utilities are responsible for reducing voltage harmonics at the point of common coupling in distribution systems.
Dispersive installation of shunt active filters on power distribution systems is a viable and effective way of solving “harmonic pollution.” The main objective of this paper is to develop a model for the shunt active filters, and to show how well the shunt active filters are effective in damping of harmonic propagation, much attention being paid to site selection. The system analysis concludes that a shunt active filter based on voltage detection has the capability of harmonic damping throughout a feeder, and that a shunt active filter based on supply current detection with differential compensation is suitable, not for harmonic damping, but for harmonic compensation of one or more non-linear loads. This paper discusses two shunt active filters based on voltage detection, which are dispersively installed on both end terminals of two feeders in a distribution system. Computer simulation verifies the validity of the modeling and harmonic damping effect of the shunt active filters for dispersive installation on power distribution systems.

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This paper describes the results of an experimental study on the characteristics of a thyristor controlled series capacitor (TCSC). At present, there are two major thyristor controlled series compensation projects in the U. S. : the Kayenta ASC and the Slatt TCSC. However, there has been little operating experience and thus further understanding of the characteristics of TCSC is still to be sought. Therefore, a laboratory-scale TCSC was produced and installed in a laboratory power system. The impedance characteristics, waveshapes of voltages and currents in the TCSC circuit, and harmonics, for various thyristor firing angles, and insertion responses were measured and analyzed. In particular, effects of the size of the circuit components, i. e., parasitic resistance, additional damping resistance and series reactor, on the overall TCSC performances were investigated. The results were compared with EMTP simulations.

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In a specified condition, I studied an optimum tilt angle of a grounded solar photovoltaic array that made a electrical energy cost cheapest, before. However, when we decide a system configuration, we have to consider a land cost and shadow of front photovoltaic arrays, and other conditions.
To solve these problems, I studied effects of cost of. sysytem components, a land cost, shadow of front phtovoltaic arrays for the optimum tilt angle and made them clear. And I made sure that the optimum tilt angle decreases according to increase of system production. And when a space between two photovoltaic arrays is fixed, the optimum tilt angle increases to reduce needed land area according to increase of land cost.
I also made sure that the best configuration of photovoltaic array for minimizing the electrical energy cost besides them.

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For fault-surge studies, the most important and also most difficult part of the simulation is the inclusion of the frequency dependence of a transmission line, because the simulation requires a high accuracy in a wide frequency range from the power frequency to a few MHz. The authors have developed a highly efficient method for modeling a transmission line considering its complete frequency dependence, which can not be dealt with the present line models in the Electro-Magnetic Transients Program (EMTP). According to the method, a transmission line is modeled directly in the phase domain, in order to avoid the modal transformation and therefore the problems of representing its frequency dependence. The method also includes sophisticated acceleration of a transient calculation by means of an Auto-Regressive Moving Average (ARMA) model. This paper presents a steady-state initialization method of the phase-domain ARMA line model for applying it to fault-surge calculations. Calculated results agree well with rigorous frequency-domain simulations, and show improved accuracy compared with an existing frequency-dependent line model (J. Marti model) widely used as a standard model in the EMTP.

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It is feared that the very high and steep lightning impulse voltage may cause electrical breakdown of the suspension insulators used in power lines. For investigation of dielectric breakdown mechanism on the suspension insulators, different porcelains were tested by applying the impulse voltage. It was found that the porcelain with non-uniformly distributed corundum had voids, resulting in lower dielectric breakdown strength. And the test results on the suspension insulator revealed partial breakdown in the porcelain before overall dielectric breakdown. The partial breakdown is considered due to high electrical stress concentration around the voids and will progress by application of repetitive impulse voltages. Also analyzed in the investigation were influences of other insulator components on the dielectric breakdown. There was found the optimum coordination of dielectric constant among porcelain, glaze and sand. In addition, electric field calculation showed that the field strength was affected by the configuration of each component.

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In order to improve the reliability of the power supply, it is necessary to prevent the lightning faults of transmission line and substation apparatus. However, the faults are caused occasionally in lower voltage power system, particularly in 77kV level. The governing factor for insulation strength of substation apparatus is lightning impulse voltage, and it is necessary to know the voltage level and distribution in a substation caused by lightning surges, in order to investigate the rational insulation coordination. For this purpose, authors have measured lightning surges at two 77kV conventional type substations from 1990 to 1993. In this paper, the characteristics of induced lightning surges and back flashover lightning surges are described. The comparison of the related surge voltages at two substations, the power line phases at grounding fault and the equivalent capacitance of substation are also discussed.

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In 1989, PCB was found in recycled insulation oils used in some pole transformers in trace of 50 mg per one kg of insulation oil, , prompting quick establishment of their safe separation method. One of prospective methods for removing such recycled insulation oils, ets. as attached and impregnated to the transformer coils may be a vacuum heating separation method which heats and vaporizes PCB under vacuum condition for separation. A proving test for applicability of the specific vacuum heating separation method was carried out with actually used transformers, which confirmed that residual PCB on coils was minimized less than a quantitative determination lower limit of 0.05 mg per one kg of insulation oil under the following standard applicable condition : vacuum of lower than 0.05 Torr ; heating temperature of 200°C; and vacuum holding time of 10 hrs., thus successfully proving insignificant effect of the treatment facility and the method on environment.

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