Control equipment of synchronous generators such as automatic voltage regulator, speed governor and power system stabilizer have been developed in order to maintain stability and to improve damping of power systems. When an operating condition changes widely, however, such controllers may become less effective because of nonlinearity of the power system.
In this paper, a nonlinear adaptive generator control system using neural networks is proposed. The proposed neuro-control system consists of two neural networks which work as an identifier and a controller respectively, and generates supplementary control signals to the conventional controllers. An essential feature of the proposed system is that the internal connection weights of both neural networks are adjusted adaptively so as to generate appropriate control signals for transient stability and damping enhancement in response to changes of the operating conditions and the network configuration.
In order to investigate the control performance of the proposed neuro-control system, digital time simula-tions are carried out for a one-machine infinite bus model system. As a result, it is made clear that the proposed adaptive neuro-control system effectively improves the system damping and shows adaptability against the wide changes of the operating conditions.

View full abstract

The electromagnetic induction interference from power line to communication line has increasingly become important problems. As the method to reduce the induced voltage, the shielded cable with aluminum sheath and iron tape has been mainly used. In order to increase screening effect of the shielded cable, the grounding resistance at the terminal of the cable must be low. But, recently, obtaining the low value of grounding resistance by usual construction method has become more difficult.
As a countermeasure against the above-mentioned problem, the method using the buried straight horizontal wire with vertical ground rod at the terminal of shielded cable is considered. However, so far, this method has been hardly investigated. Then, as a basic study of this method, authors carry out the theoretical analysis of screening effects for two models [in the case of model (a), the wire completely does not have infulence of induction from both the power line and shielded cable, and in the case of model (b), the wire has infulence of induction from both of them].
In this paper, the analyzing methods of screening effect for these two models are clarified. Furthermore, knowledges obtained from calculated results and the attention points in the practical earthing design of this method are clarified.

View full abstract

Experiments on the lightning-induced voltage on an overhead wire with a simulated lightning channel have been carried out outdoors. They have advantages because uncertainties of the parameters related to the lightning channel are greatly reduced, and repeated measurements are possible.
In this paper, the influence of the electrical characteristics of the ground on the lightning-induced voltage on an overhead wire, associated with a vertical return stroke channel, is studied with a 1/20 reduced-scale model, together with the influence of the termination of the wire. The conductivity and relative permittivity of the ground are evaluated by the coincidence of the measured horizontal electric field with that calculated from the current on the simulated lightning channel.
Irrespective of the termination of an overhead wire, measurements verify calculated results based on the theory where the inducing sources of the voltages are looked upon as tangential components of electric fields to the wire.

View full abstract

As the load in a power system continually changes, it is important to regulate the generator operating point. In this paper, assuming a suitable operating range for the generator the regulations for typical generator operating points within this range are selected and then fuzzy controllers are designed accordingly. To investigate the adaptation of each controller, a considerable number of simulations are carried out for the various operating point changes. By investigating the control performance of the adaptive controllers quantita-tively, a design method for fuzzy controllers for generator operating point regulation is proposed. Further-more, a comparative estimation of the fuzzy control formula and optimal control formula with an observer is made using a common quantitative criterion. In addition, a one-machine infinite-bus system including limits on the AVR and governor is used as the control object model.

View full abstract

To satisfy demands of fast calculation in power system analysis, utilizing of the parallel computer is being studied and various parallel algorithms are being developed. System decomposition methods and iterative methods are usually applied to parallel computing due to their parallelism. LU decomposition methods, i. e. direct methods, is also utilized its operating parallelism. However, because of the medium in size or the sparsity of power system matrices, it is difficult to gain a speedup ratio so suficient as the increment of processor number in the region of the large processor number.
Author studied to exploit more parallelism in the LU decomposition, and developed a new parallel algorithm “parallel elimination method” mentioned details in this paper. This method is verified its effectiveness in large number rigion of processors by simulations counting the number of operation units.

View full abstract

This paper presents a real time identifying method of the optimal operating point of PV modules using a neural network. The maximum power from PV modules depends on the environmental factors such as insolation and cell temperature. Therefore, the PV systems need accurate on-line identification of their optimal operating points in order to yield maximum power supply from the systems. The measurements of the short-circuit current and the open-circuit voltage on the cells monitoring the PV modules are required for the real time estimation of optimal operating point. By using the measured data from August 1992 to July 1993, the efficiency of the proposed method has been evaluated with highly accurate estimation on four types of the poly-crystalline silicon PV modules.

View full abstract

The number of line ground faults by lightning on 500KV transmission lines has been reduced significantly during the past ten years. This is because the three-ground-wire system, which has been installed instead of the two-ground-wire system, plays an important role.
Where the ratio of voltage across the insulator horns in the two-ground-wire system was 1.0, the measured horn-to-horn voltage ratio was reduced to 0.40_??_0.64 by adapting the three-ground-wire system.
Measurement showed the voltage ratio became much smaller (0.33_??_0.57) after suspending a 77KV XLPE cable from the tower top to its foot, with the cable sheath connected at each tower arm.
These measured voltage ratios were in fairly good agreement with the calculated values obtained by the EMTP method.

View full abstract

In this paper, in order to determine the optimal radial power system structure rapidly I propose to use a chaotic neural network model with the constrained noise approach which can obtain the global minima. When a radial power system has a number of connected feeders, the combinatorial number for possible system structures becomes too huge. Determination of the optimal system structure from a great number of combinations becomes a combinatorial optimization problem, and it has been difficult to solve this type of problem quickly with conventional algorithm so far. However, with the chaotic neural network model, it has become possible to carry out the optimization efficiently. Furthermore, in order to operate the radial power system more securely, I employ a network switching scheme so as to obtain a more practical system structure considering cases of fault occurrence at each substation. The technique is demonstrated with an actual 21 substation system. The proposed method is compared with a Hopfield neural network model approach.

View full abstract

Desingn of power systems for meeting increase of electric power demands is be-coming more difficult and complex. One of the reasons is increase of the fault current. As one of the most effective methods for suppressing the fault currents, installation of fault current limiters are expected.For the above purpose, superconducting fault current limiters(SFCL's) are being developed.We have already given analitical solutions on fault current in power systems with SFCLs.
This paper discusses determination of specifications of SFCLs, and besides. effects of limiting the fault currents due to SFCLs by use of the model systems of one machine-infinite bus with single and parrallel transmission lines.

View full abstract

Faults may occur in transmission lines due to various causes, including wind, salt, rainfall, snow-fall, contact with wildlife and flying objects. When these types of faults occur, current and voltage waveforms undergo various changes depending on the particular cause. Since these changes are character-istic of the particular cause of the fault, it is possible to predict the cause of a fault based on these waveform characteristics. Therefore, we conducted artificial fault testing on an actual system scale to clarify the relationships between fault causes and changes in current and voltage waveforms.
Moreover, it was confirmed that the cause of a fault could be determined at a high rate of accuracy by the multi-discriminant and the neural network analysis. As a result of examination and evaluation of these findings, it was found that it will be possible in the future to automate the location of faults and their causes that have thus far been dependent on manual fault detection operations by maintenance personnel.

View full abstract

Line impedances were measured for frequencies from 1 to 500KHz. The high resistive-impedance distorted the propagation wave, and the distortion generated sine wave oscillation. The sine waves were superposed on transient voltages of the propagation wave on a multi-conductor system. The voltage waves by the proposed method in the paper showed a good agreement with the measured results.

View full abstract

Global warming is one of the most serious issues in the modern world. Various innovative technologies have been proposed worldwide to reduce CO₂ emission and thus mitigate global warming. Among these technologies are, for example, 1) the WENET project launched in 1993 by the government of Japan which aims at transporting energy produced by photovoltaics or hydro power systems in the vast areas such as Sahara desert far from demand sites in terms of hydrogen, and 2) the hydrocarb process proposed by Steinberg which will coprocess fossil fuels and biomass into carbon and methanol.
Japan is among resource-poor countries but has an advantage that it is located relatively close to Southeast Asian countries and Australia which are endowed with vast space and solar energy. The objective of this paper is to investigate how much these innovative technologies be introduced in Japan and the surrounding resource-rich regions in the coming 30-40 years.
An energy model of optimization type has been developed for this purpose and model simulation results provide a number of interesting suggestions on the future strategies for Japan to mitigate global warming.

View full abstract

Power generation experiments have been performed for disk type MHD generators with different channel shape. The increase of enthalpy extraction ratio by enlargement of area ratio has been shown experimentally and the highest enthalpy extraction ratio of 18.0% has been achieved with the area ratio of 6.9. Experimental results have also shown that for the generator with large area ratio, wall static pressure in the MHD channel is kept lower than that for the generator with small area ratio. These results suggest that high Hall parameter can be obtained by enlargement of area ratio. Further we can see that we have to optimize area ratio of both the channel and the supersonic nozzle for optimum generator design. Finally, the effect of fluctuation of seed fraction on power output is discussed. It can be pointed out that more than 20% of enthalpy extraction can be realized when seeding system can be improved to eliminate fluctuation in seed fraction.

View full abstract