This paper presents a class of new variants of an exact decoupled load flow approach in rectangular coordinates, which are capable of achieving the quadratic convergence behavior similar to that of the standard Newton-Raphson (NR) load flow. The proposed variants employ no assumptions in their derivation and use Maclaurin series to preserve fully the effects of the decoupling as well as other variations in the Jacobian during the iterative process. To make the proposed variants convergent to a wide range of load flow problems, the modifications based on the convergence condition of the Maclaurin series are employed in such a way as to cause no changes in the sparsity structure of Jacobian matrix and with minimal additional computation burden. The convergence performance of the proposed variants is studied by performing load flow simulations on a work station for various standard IEEE test systems and in general, is confirmed to follow closely the quadratic convergence of the standard NR method.

抄録全体を表示

For transmission-line surge studies, the inclusion of corona discharge due to high voltage surges is important as well as the inclusion of frequency-dependent effects. Because the charge-voltage (q-v) curve of a lightning surge is different from that of a switching surge, a corona model should reproduce different q-v curves for different wave-front times. The present paper proposes a wave-front-time dependent corona model which can express the dependence by a simple calculation procedure as accurately as a rigorous finite-difference method which requires an enormous calculation time. The simplicity enhances the implementation of the corona model into a line model, because a large number of the model is to be inserted into the line model by discetization. The calculated q-v curves by the proposed method agree well with field tests. This paper also proposes an efficient method to deal with nonlinear corona branches in a distributed-parameter line model using the trapezoidal rule of integration and the predictor-corrector method.

抄録全体を表示

Hydrogen absorbing alloys have a number of useful functions, such as energy conversion, hydrogen storage and purification. As an application to separation and purification of hydrogen, we have developed a new hydrogen purification system by using a hydrogen absorbing alloy for generator cooling.
For demonstration testing with an actual machine, a hydrogen recovery and purification device using 120kg of alloy was manufactured and installed on No.5 turbine-synchronous generator at Himeji No. 2 power station. This device is designed to improve the purity of the hydrogen gas in generator containing impurities such as nitrogen and oxygen. The test results tell that the purity of the hydrogen gas in the generator can be enhanced from 98% to 99.9% and maintained at this level under continuous operation. An application of the hydrogen purification system is expected to decrease the generator's windage loss, resulting higher generator efficiency.

抄録全体を表示

Numerical investigations are carried out on nonequilibrium disk MHD generator with 100MW thermal input using cesium seeded argon as the working plasma, which is suitable for a future large scale experimental plant. At first, channel configuration and nominal conditions of a generator with sufficiently high performance are determined by design calculation and it is confirmed that the generator is stable and functions as designed at the nominal operating condition. Simulations of the performance of the designed generator at light-load condition are carried out and it is indicated that the segmented load connection scheme is effective to prevent the performance deterioration caused by the ionization instability. Next, simulations are carried out in the case impurities are contained in the working plasma and the influence of their concentration on the generator performance is made clear. It is also indicated that designs of the generator with high performance under the contaminated condition are feasible if the ingredients of the impurities and their concentration are known even in the case the impurity concentration is fairly high and the generator designed without impurity is not suitable for the plant.

抄録全体を表示

A 500kV-rated thyristor valve is being developed for use in a 2800MW-500kVdc system. One aim of this development effort is to reduce valve size by adopting a rational insulation design. We studied optimization of the air-gap insulation between the upper and lower thyristor modules and of creepage insulation distance of insulation poles, both being considered to make the greatest contribution to size reduction. An electric field analysis was performed to determine the air-gap insulation. Next, a module-to-module insulation model was manufactured to verify the adequacy of the analysis. A long-term dc V-t characteristic (voltage-time characteristic) for insulation poles under postulated environmental conditions was obtained to optimize creepage insulation distance of the insulation poles. Such a rationalized insulation design combined with the adoption of an 8kV light-triggered thyristor offered us a prospect of reducing the height of the thyristor valves by about 25% and the volume by about 30% compared with those designed by the Hokkaido-Honshu DC Link design method. We also investigated the change in insulation characteristic caused by cooling water leakage.

抄録全体を表示

In planning a distribution system for urban area, when a feeder is newly installed, the route of the feeder must be determined among many candidates, considering investment cost and constraints. However, it is difficult for planners to find the optimal route of the newly installed feeder. Because too many candidates of route exist which can be constructed along the road on service area of the power company. It must be considered whether the end part of an existing feeder can be used as apart of newly installed feeder within specified loaded value. In this paper, in orderr to support planners' decision for selecting optimal route of newly installed feeders, the authors have formulated the problem mathematically, and propose a new solution algorithm to find the optimal route by referring Dijkstra Method. Through numerical examples, authors demonstrate the validity of the proposed method.

抄録全体を表示

High voltage DC stress is applied to oil immersed insulation in the AC/DC converter transformers and DC reactors. Understanding of streaming electrification phenomena due to oil flow under DC stress is very important to achieve reliable insulation design for these apparatus. A model duct with a closed oil loop, which simulates a path of the oil flow in the actual shell type power transformer, was constructed. Partial discharge generation by streaming electrification under AC, DC and AC/DC superimposed voltage was investigated by varying the oil temperature, oil flow rate and applied voltage. As a result, partial discharge at lowest oil flow rate was found to occur at the temperature of 70°C. Although the oil flow rate to generate partial discharge shifted toward lower value with the increase of voltage under both AC and DC stress, DC stress showed less effect on the partial discharge generation than AC stress which gave the same oil gap stress. It is concluded that these experimental results give useful knowledge for the insulation design of AC/DC converter transformers and DC reactors.

抄録全体を表示

This paper describes a new method for studying unit commitment in a competitive electricity industry. A number of large generating units are modelled, each making price and quantity offers into a simple dispatch market. Demand for electrical energy randomly fluctuates and there are a number of centrally dispatched, flexible, high priced generators. Genetic algorithms are used to determine the profit maximising commitment decisions and market offers of each generator.

抄録全体を表示

Network parameters in power systems are necessary to calculate bus voltages, currents, and powers. Therefore accuracy of network parameters is very important to get hold of the condition of power systems exactly. However generally, we regard them as constant. Thus accuracy of network parameters and calculated state values may be deteriorated. Recently, studies on Global Positioning System (GPS) for power system monitoring are being carried out in many fields. Because of high accuracy of GPS's time signals, we can calculate phase angles simultaneously from waveform of bus voltages or currents. By using this information, we can estimate more accurate network parameters and consequently state values.
In this paper, we propose a new method of on-line network parameter and state estimations using phase angles which can be calculated by GPS and power system information (bus voltages, power flows, line flows). By doing the estimation, improvement in accuracy of network parameters and all sorts of calculations in power systems is expected.

抄録全体を表示

The authors deal with an initial stage of partial discharge inception phenomena at the triple junction formed in GIS. Partial discharge inception voltage (V_c) was measured by optical method during the application of positive lightning impulse voltage as parameters of the surface condition of electrode, and SF₆ gas pressure. As a result, the followings were obtained. (1) V_c is not affected by the surface condition of the electrode. It seems that initial electrons are supplied from negative ion, SF₆^-, in the space charges formed by electron avalanche due to high field strength near the triple junction. (2) Covering the electrode with dielectric film is effective to the relaxation of the electric field near the triple junction. Therefore V_c for the dielectric coated electrode is higher than that for the bare electrode.

抄録全体を表示

This paper presents a new, practical method of simulating the behavior and the shape of arcs driven by magnetic force in a gas. This simulation method is very useful in designing electric devices using magnetically driven arc technique. First, we describe the arc model. In this model, the arc is assumed to be a chain of small rigid cylindrical current elements. Each element receives Lorentz's force from the magnetic field and a fluid drag force from the surrounding gas. Owing to the similarity between an arc and a rigid column, the drag force of the arc is expressed by that of the column. The element moves with the velocity determined by these forces. Consequently, we can obtain the behavior and the shape of the whole arc. Finally, a simulation example is shown. We have obtained the arc is given the spiral shape by the magnetic field. This simulation result illustrates the observation of arc.

抄録全体を表示

Measurement of impedance of a transmission tower by the direct method is investigated by Numerical Electromagnetic Code (NEC-2). The arrangement of the measuring wires in the experiment influences the result, and it is possible to correct the measured tower surge impedance to that for a standard arrangement with a vertical current injection wire and a horizontal voltage measuring wire. By reviewing various experimental results in this way, it is concluded that an independent doublecircuit transmission tower has impedance of about 150Ω with the traveling wave speed in the tower being equal to that of light. This value can be applied to the case of direct hit of lightning to the tower top, regardless of the type of lightning, upward or downward.

抄録全体を表示

The present paper proposes a new type fault current limiter (FCL), which consists of a high T_c superconducting (HTS) element and two coils wound on the same core without any leakage magnetic flux. In this FCL, either the limiting impedance or the initial limiting current level can be controlled by adjusting the inductances and the winding direction of the coils. Therefore, this FCL could relax the material restrictions on high T_c superconducting FCL. A current-limiting experiment by a model FCL was carried out, and the limiting performance was observed. The initial limiting current level of the model FCL was 1.7 times as high as the critical current of the HTS element, and the fault current is suppressed down to 52% immediately after the short-circuit in the test. Considering a voltage-current characteristics of a high T_c superconductor in a computer simulation, the calculated results almost agreed with the experimental results.

抄録全体を表示

Surge arresters are sometimes damaged by lightning strokes with high energy, in spite of installation of a conventional protection method. In order to reduce the number of failure of surge arresters, we should consider another protection method, such as increase of withstand capability of surge arresters and installation of additional overhead ground wires. However quantitative comparison of these methods for preventing damages of surge arresters against lightning strokes with high energy has never been performed.
This paper describes effects of additional overhead ground wires for preventing damages of surge arresters. The main results are as follows:
(1) The failure rate of surge arresters on a distribution line with two overhead ground wires is about 3 times smaller than that with a overhead ground wire.
(2) Installation of the second overhead ground wire of 6_??_8 spans from the termination of a line is as effective to reduce the failure rate of a surge arrester at the termination as increasing of withstand capability by a factor of two.

抄録全体を表示

A local linear perturbation analysis and a channel-length scale linear stability analysis are carried out for coalfired subsonic diagonal type MHD generators of commercial scale. Disturbances in subsonic flow propagate with downstream traveling waves and upstream traveling waves, and those waves reflect at inlet and exit boundaries. The local linear perturbation analysis examines the local growth rate of traveling waves which is determined by a dispersion equation. The channel-length scale linear stability analysis, which is based on the characteristic equation derived from the inlet and exit boundary conditions, judges whether the waves grow or decay during their propagation and reflection. The local linear perturbation analysis shows that a conventionally designed channel with near-sonic velocity has a large wave-growth rate and tends to be unstable. A newly designed channel with relatively low velocity has small wave-growth rates. The channel-length scale linear stability analysis indicates that disturbances in the conventionally designed channel grow during their propagation and reflection. The channel-length scale analysis also shows that the newly designed channel can be stably operated. Time-dependent calculations are carried out to verify the results obtained from the linear stability analyses.

抄録全体を表示

This paper proposes a new method for the forecast of daily maximum electric load by using feedforward neural networks and recurrent neural networks. While the maximum electric load mostly depends on the weather conditions of the day, it is important for the forecast to consider the influence of the load or the weather conditions for the past few days. The proposed method consists of two steps in the learning stage. In the first step, the feedforward networks learn the standard electric load corresponding to the weather conditions of the day in which the load is to be predicted. In the second step, the recurrent networks learn the difference between the standard electric load and the measured one. The load forecast is executed as follows: the feedforward networks output the standard load after the weather conditions of the day are inputted. The final result of the load forecast is obtained as for the output of the recurrent networks which correct the standard load considering the time dependency of electric load. Computational experiments show the high abilities of the proposed method so that the annual average error of the forecast for weekdays is 1.7%.

抄録全体を表示