In recent European and American countries, research on FACTS (Flexible AC Transmission System) apparatus using power electronics techniques is becoming active. One of the objectives is to increase transmitted power through power system using control equipment such as TCSC (Thyristor Controlled Series Capacitor and UPFC (Unified Power Flow Controller). This attempt may be available in power systems which are tightly connected through many loops.
This paper deals with the optimality of load flow control of power system with many loops . In this paper, three kinds of linear or nonlinear programming problems are formulated. The first one is the maximum flow problem under the condition that growth rate of each generation and load node is given. The second one aims at minimizing the var-loss of the whole power system using FACTS apparatus under the condition that the power system transmits the maximum power obtained in the first problem. The third problem is to minimize the capacity of installed FACTS apparatus under the condition that var-loss of power system is kept equal to the minimum value obtained in the second problem. In this problem, installation points and capacities of FACTS apparatus are assumed as the only controllable parameters.
At first, the effects of FACTS apparatus from the viewpoints of the first and second problems axe discussed and some important results are obtained. Secondly, using these obtained results, three problems shown above are formulated into linear or nonlinear programming problems in three steps using DC flow calculation method. Each problem is solved sequentially using the results obtained in each previous step. Thirdly an example of calculation is shown using model power system. The solutions obtained above are compared with those, obtained by using the conventional AC flow calculation to study the calculation accuracy of the proposed method. Finally, the first and the third problems are formulated into two steps linear or nonlinear problems. It is demonstrated that the solution is not always equal to the solution of the problems in three steps discussed before.
The proposed formulations can be used not only for the determination of optimal installation points and optimal installed capacities of FACTS apparatus but also for the evaluation of FACTS apparatus from the points of load flow control in large scale power systems because the proposed techniques are simple and all of the constraints are linear and sparse.

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This paper presents a regression based daily peak load forecasting method using multiple years data with trend cancellation and trend estimation techniques. Daily peak load heavily depends on temperature in daytime and is influenced by the other weather factors such as humidity. Since a characteristic of the load is varying, peak loads just before a forecasting day are more significant for the forecasting. The regression model can represent relationships between these weather factors and peak loads. However, the forecasting model is sometime not adequate for precise load forecasting. The regression model is well matched with the late data, but the model causes large forecasting errors in transitional seasons because of seasonal change of load characteristics. In order to forecast precisely through a year, a method of using seasonal or whole year data in past years is proposed. In this paper, two kinds of trend data processing techniques are described. The first is trend cancellation. The second is trend estimation. The trend cancellation technique removes annual load growth by means of division or subtraction processes with morning load on the forecasting day. The trend estimation technique estimates the trend between the forecasting year's load and the past year's load by using the variable transformation techniques. Performance of the both techniques verified with simulations on actual load data is also described.

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Technological problems of fuel cell generation systems have been overcome mostly; if fuel cell manufactures succeed in reducing the production cost, a number of fuel cells will be installed in distribution systems. Therefore, it is important to prepare a policy to evaluate the merit and demerit of fuel cell installations beforehand.
In our previous study, we have proposed a framework to optimally introduce fuel cells into distribution systems. According to this framework, an optimal deployment planning of fuel cells has been formulated as a mixed integer programming problem and the authors have developed a solution algorithm based on the Branch and Bound method. For large scale systems, however, a combinatorial explosion makes the algorithm unable to search the optimal solution within a reasonable computation time.
In this paper, a solution method using the genetic algorithm technique is proposed to find suboptimal solutions for large scale problems. Genetic algorithm is belonging to multi-agent search algorithms and shows a robust characteristic against a multi-modal objective function like this problem. The proposed algorithm exploits two kinds of techniques to improve its performance: The first is the diploid population and the second is the efficient initialization. The former contributes the preservation of genetic variety and the latter accelerates the speed of convergence. The proposed algorithm has been applied to various example systems and compared with a simulated annealing method to evaluate their performances with successful results.

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Voltage reactive power control (VQC) on power systems becomes difficult when a load increases or decreases rapidly, especially in the morning and at noon. This is caused mainly by two problems. One is delayed operation and the other is noncooperative operation of facilities. To solve these problems, an advanced method for a centralized feed-forwarding control system and algorithms are pre-sented. They are based on two main steps, forecasting power system state for several minutes and dispatching reactive power sources optimally based on stepwise linear programming. The proposed method is evaluated and tested for data of a large scale power system. Results show that the proposed method keeps the voltage constraints well and reduces redundant operation of facilities.

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We developed optical voltage and current transformers (PT and CT) for 72kV three-phase in one enclosure type Gas Insulated Switchgears (GIS). We used Bi₁₂GeO₂₀and flint glass as device material used in the optical PT and CT, respectively. We also designed an optical PT unit with a pin hole type grounded electrode and intermediate electrode in the pin hole and an optical CT located at the ground level with optical transmission by an optical fiber instead of free space light propagation. We assembled the optical PT and CT into GIS and conducted withstand voltage test, ratio error characteristic test, and other-phase influence test, obtaining good assessment results. Finally, we suggested that the developed optical PT and CT have a possibility of practical use.

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It is known that Ferrography analytical method can find the unusual state of the bearing surface of the rotating machine with a higher sensitivity than that of other monitoring methods, such as the measurement of frictional force, frictional temperature and rotational speed. This method can detect the abnormal wear particles, such as cutting wear particles, spherical particles, sever wear particles and black oxide particles, before the frictional force and temperature caused the unusual change and rotational speed decreased. However this method requires considerable operator skill to distinguish the wear particles. We applied image processing techniques and artificial Neural Networks using a computer to Ferrography analytical method. It was shown that our proposed system could distinguish the wear particles well.

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In this paper, a correction method of LLS (Lightning Location System) location error under fuzzy reasoning is proposed. LLS is a useful tool to inform lightning location to the dispatchers of Power System. However it has not enough accuracy of lightning location because of the direction error of antennas, the propagation error of radio wave, the disturbance of radiation from near structures and the random noise. In particular, the disturbance of radiation from near structures has serious influence on the accuracy of lightning location. To restrain the disturbance of radiation and to correct the location error, a fuzzy reasoning scheme is introduced. The fuzzy rules are automatically adjusted by a tuning law so that the location error between the actual lightning location and the LLS detecting location converges to zero. Simulation results demonstrate the effectiveness of the proposed fuzzy correction method for improvement of the accuracy of LLS.

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So far a single-stage neural network has been proposed to forecast insolation of next day. In the present paper, a multi-stage neural network is developed to reduce forecasting error further. A first-stage neural network forecasts average atmospheric pressure of next day from atmospheric pressure data of previous day. A second-stage neural network forecasts insolation level of next day from the average atmospheric pressure and weather data of previous day. A third-stage neural network forecasts insolation of next day form the insolation level and weather data of previous day. Meteorological data of Omaezaki, Shizuoka at April 1994 are chosen as input data. The insolation values forecasted by the multi-stage and the single-stage neural networks are compared with the measurement ones. The results show that the forecasting error is reduced to 24% (by the multi-stage) from 33% (by the single-stage).

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Partial discharge (PD) may take place due to residual defects like metallic particles in SF₆ gas insulated power apparatus such as GIS, However, the signal of PD occurring in SF₆ gas is very weak and susceptible to external noises in air. Moreover, because of the complicated mechanism of PD, the radiation property of electromagnetic wave from PD has not been clarified, yet, Therefore, it is hard to distinguish the PD signal in SF₆ gas from the external noises.
From the above points of view, we have been investigating the radiation mechanism of electromagnetic wave from PD. We measured the polarization characteristics of electromagnetic wave radiated from PD in comparison with that of half-wave dipole antennas. The polarization characteristics of PD was explained by the theory of half-wave dipole antenna, rather than that of an infinitesimal dipole antenna. Moreover, we compared the power spectrum received from PD measured by a biconical antenna with that received from the half-wave dipole antenna or infinitesimal dipole. It was found that the power spectrum for PD also corresponded to that for the half-wave dipole antenna with 50cm length.

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The sintering characteristics and physical properties were investigated for several Ni/YSZ powders, prepared using NiO powder and commercial YSZ or calcined YSZ powder. The sintering shrinkage of Ni/YSZ powder was affected by the kind of YSZ powder used; larger shrinkage was observed for cermets made from commercial YSZ. The shrinkage was also considerably affected by the amount of NiO used. The sintering-starting temperature was also affected by the YSZ powder used; it was higher for Ni/calcined YSZ cermets. The shrinkage characteristics in the sintering-temperature region were predominantly affected by the amount of NiO used. The amount of NiO strongly affected the isothermal shrinkage characteristics, based on the observation that all of the cermets investigated showed a shrinkage profile similar to that of NIO.
The porosity and conductivity were increased on the Ni/calcined YSZ because of the localized NiO distribution in the sintered body.

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For high voltage induction motors of large ratings, new driving systems such as inverters using Pulse Width Moduration (PWM) are becoming popular in industrial plants using mill motors and traction motors. Understanding of the partial discharge characteristics under inverter voltage stress is very important to achieve reliable insulation design for these apparatus. A model sample with a single void in insulation and IEC (b) electrode system for surface discharge on insulation were used. Partial discharge inception voltages under ac voltage stress, unipolar rectified ac voltage stress and unipolar rectangular step pulses were investigated by varying the applied voltage. As a result, it was found that the zero-to-peak value of partial discharge inception voltage under unipolar voltage stress was 1.5 to 2 times higher than that under ac voltage stress. This reason can be attributed to the behaviour of the residual voltage after discharge at the void since the occurrence of the partial discharge inception voltage under unipolar stress is considered to be higher than under ac stress.

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The audible noise which is produced by corona discharge from transmission line conductors is composed of two major components, namely “hum noise” and “random noise”. Hum noise has a frequency of twice the power line frequency and is generated primarily in rain, fog, and highly humid environments. It is one of the major factors affecting conductor design of transmission lines for voltages above 500kV and it is very important to predict level of hum noise near transmission lines.
In this paper, through comparison between measured values in the UHV Akagi test line and that using corona cage, an experimental prediction method of hum noise in rain condition is proposed.

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This paper deals with the results of various partial discharge detection tests designed to clarify fundamental characteristics, which were carried out on a real-scale 275kV GIL test line laid through a tunnel, along with a solid partial discharge testing technique for a long-distance GIL.
Where it is required to secure dependable reliability for a long-distance and large-capacity gas-insulated transmission line ( GIL), strict quality control and electrical tests carry serious weight with verifying its integrity, during the construction work.
Among others, “Partial Discharge Detection” is extremely instrumental in examining GIL insulation for defects or damage. But its performance has not yet been fully brought to light, namely, sensitivity to faint signals from incidental partial-discharge. how the detection is influenced by assorted modes of external noise. and whether or not to catch how faint partial discharge signals act in a long-distance transmission line . In particular no dependable partial discharge testing technology was available for long gas-insulated transmission lines.

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Experimental investigations of the breakdown mechanism in SF₆ gas by model electrode configurations are performed for DC and lightning impulse voltages. Electrodes are composed of a rod to a disk. The gap distance is adjusted by changing the radius of the rod electrode. The amount of gap distance and rod radius is kept constant(15mm). Some peculiar phenomena of breakdown characteristics on the gas pressure and the gap distance were observed. The maximum DC breakdown voltage as a function of gas pressure are given at 0.3MPa for both positive and negative polarities except the gap distance of 7.5mm. At the condition of gap distance of 7.5mm, the breakdown voltages monotonously increase without the crest value as increase of the gas pressure for both polarities. The DC breakdown voltage in the gas pressure of 0.3MPa is higher than that at lightning impulse voltage at some conditions of the electrode configuration. The lightning impulse breakdown voltages have same values for both polarities and also they are same as that of DC voltage in gas pressures of 0.2, 0.3 and 0.4MPa under some conditions of the electrode configuration.
These results are well analyzed by taking account of (a) an electric field distribution without space charge and (b) a schematic distribution of negative and positive space charges.

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Long-distance SF₆ Gas Insulated Transmission Line (GIL) has been developed for huge power supply in future. To enhance the reliability of GIL operation and to diagnose the insulation performance in GIL, partial discharge (PD) measurement is one of the expected technique and thus we measured the frequency spectrum of PD current pulse and that of electromagnetic wave radiated from PD on full scale, long distance 275kV SF₆ GIL.
In this paper, by analyzing these spectra we carried out the comparative study of different types of PD sensor like UHF, foil electrode and search coil sensors, as well as the attenuation characteristic of PD signals in long distance GIL. The result of the experiment shows that under 100MHz, both UHF sensor and foil electrode sensor have enough high sensitivity, whereas above 100MHz, UHF sensor has better sensitivity than other sensors. Furthermore, we estimated that the attenuation ratio of electromagnetic spectrum measured by UHF sensor was 5.9 [dB/100m] in the frequency range from 200 to 500MHz. Finally, we concluded that UHF sensor has the best performance from the viewpoints of sensitivity and frequency characteristics, for PD measurement in GIL.

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We observed current pulse waveforms of partial discharge (PD) in 275kV full scale 168m length gas insulated transmission line (GIL). We also investigated voltage phase dependency and frequency characteristics of electromagnetic wave emitted from PD. From these results, we discussed mutual relationship between PD current waveform and emitted electromagnetic wave characteristics. Furthermore, we discussed the propagation characteristics of PD signal in long GIL.
In this paper, we described the generation, propagation and detection characteristics of PD signal in GIL and finally, we could estimate the attenuation rate of the PD signal in long GIL.

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In Japan, long distance Gas Insulated Transmission Line (GIL) technique has been developed and now is being constructed for future huge electric power transmission. In GIL, if there would be a small defect such as void and metallic particle, partial discharge (PD) would occur, thus detecting PD is an effective method for insulation diagnosis in GIL. Among the PD measuring method, detecting electromagnetic wave generated by PD is one of the most effective method because PD radiates wide-frequency electromagnetic wave up to UHF.
This paper describes the experimental result of simultaneous measurement of PD current pulse and its electromagnetic wave in full-scale long distance 275kV GIL. The result, shows that firstly, PD signal with 1_??_2pC can be detected at the point of 169.5m away from PD source using UHF sensor. Secondly, the propagation velocity of electromagnetic wave in GIL is nearly equal to the light velocity. Thirdly, electromagnetic wave magnitude is attenuated about 7.5dB at the point of 100m away from PD source. Moreover, time-frequency analysis (wavelet analysis) of waveforms shows that the attenuation rate of electromagnetic wave differs depending on its frequency.

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