Switching operations in gas insulated switchgears (GIS) can generate very fast transient overvoltages (VFTO) which propagate in the GIS with little attenuation. When a transformer is directly connected to the GIS through a gas/oil bushing, the VFTO can enter the transformer and excite the voltage oscillation in the windings. In the paper, we firstly show a resonance phenomenon due to the superposition of the traveling waves which was found in the experiments using the coil windings of a 500kV transformer. The fundamental resonance frequency ranged at about 2MHz and its voltage at the intertum (turn-to-turn) of the coil could reach 0.25 times of the applied voltage in the worst case. Secondly, the electrical breakdown properties of intertum insulation in oil were studied, applying the unipolar and bipolar voltages with 2MHz oscillatory frequency. The breakdown voltages at the unipolar and bipolar VFT oscillatory stresses were about 1.25 and 1.40 times higher than that at the standard lightning impulse, respectively. We discuss the experimental breakdown stresses with the ones estimated from the analysis of VFTO in the transformer windings and also show the methods to cope with the VFTO.

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Formerly, there were pulse radar and Murray loop bridge in cable fault location method that is applicable for branch line. Those methods need terminal connection at far end. Therefore, it is trouble in fault location for branch line. Pulse radar is applicable for only high resistance ground faults and Murray loop bridge is applicable for only low resistance ground faults.
We developd current detection pulse radar and tested it. In high resistance ground fault location measured result includes discharge delay error. Therefore, we proposed an error correction method and confirmed it. And we designed a new cable fault location method of pulse radar and tested it.

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Partial Discharge (PD) within voids in solid insulating system is a symptom and/or a direct cause of a deterioration of stator windings of a turbine generator. The bandwidth of the electromagnetic waves emitted from PD is very broad and ranges to GHz. We developed a new system based on “Spatial Phase Difference Method” for detecting microwave (GHz) emitted from PD. In this paper we applied this system to two off-line turbine generators in the overhaul and an on-line turbine generator which has two built-in antennas. On-line PD detection of the turbine generator is very useful for recognizing abnormal and/or deteriorated stator winding insulation without a machine outage. It was found that the detection system was able to detect microwave emitted from PD in operating turbine generator.

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A research committee organized in the Institute of Electrical Engineers of Japan (IEEJ) carried out a series of intercomparison tests using a lightning impulse voltage measuring system which was developed by another research committee as one of the Japanese national standards. This project was performed as a final technical check to establish an accreditation system for measuring lightning impulse voltages in Japan. Ten organizations participated, of which eight were manufacturers, implying that the tests were very realistic and practical. The tests ensured the prospects of establishing the accreditation system.

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Dry batteries and rechargeable batteries such as Ni-Cd batteries and Ni-MH batteries are widely used for uniterruptible power supplies and portable terminals. In the design of battery-powered equipment, circuit simulation is often conducted. In conventional simulations, the battery is generally treated as a voltage source, but it would be better to consider the battery's electrical characteristics, such as its internal impedance and the current and voltage characteristics at discharge and charge conditions. The electrical characteristics of secondary batteries have mainly been studied for diagnosing battery deterioration, in which only the battery impedance is considered.
This paper presents an equivalent circuit of a secondary battery that is suitable for power circuit simulation. This equivalent circuit expresses the transient characteristics and the current and voltage characteristics for discharge. The equivalent circuit of a Ni-Cd battery is confirmed by simulations and experiments.

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This paper deals with the partial discharge inception voltage(PDIV) and breakdown voltage(BDV) characteristics of turn-to-turn insulation models for oil filled transformers under steep front short duration pulse voltages, of which wave forms are 35/70ns and 50/370ns. It was found that BDV's under nano-second pulse were 1.2_??_1.4 times higher than those under standard impulse voltage.

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In order to realize an anto-detection system of a single pulse of partial discharge in power cables, a neural network (NN) system with very fast computation (no more than I ms) are desired. In this paper, we present a trial manufactured auto-detection NN system using an analog parallel circuit. The feature of this system is adoption of a Random Weight Change learning algorithm, which is suitable for the analog processing without smooth sigmoid function. Experimental results of a manufactured circuit are also investigated.

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In order to establish practical measurement method for particles in oil, this paper verifies several problems on the particle counting measurement, e. g. sampling container and its cleaning way, solvent, sampling points, sampling way, previous treatment, particle counting equipment, the method and the calibration.
Based on this established measurement method, authors introduce several results of the particle measurement of the oil sampled from actual transformers under factory test, the transformers in field.
From these results, authors tentatively suggest the concrete classification of oil cleanness in the transformers.
And authors report the data to have been in pursuit of the change of the dielectric oil strength with the filter-circulation. Moreover, authors discuss the relationship between the number of particles-in-oil and the dielectric strength.

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A new adaptive fuzzy control method is developed for reduction of fuel consumption of a diesel generator in a photovoltaic/wind/diesel generating system with a battery. The adaptive fuzzy control method takes two steps of fuzzy inferences. The first fuzzy inference predicts whether the system situation tends to power shortage (s=0) or power surplus (s=1). The input data to the first step are the photovoltaic/wind generator power output P_PW and the load demand P_L. The second step fuzzy inference determines the diesel generator output. The input data to the second step are s, P_PW, P_L and the battery charging state. The fuzzy control rules ofs=0 and s=1 are framed by referring to time series results of the system operated by the dynamic programing which is the optimum operation method if time series values of P_PW and P_L are known. The simulation results show the new adaptive fuzzy control method effectively utilizes the battery to reduce the fuel consumption and suppress the fluctuation of output of the diesel generator.

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As the world wide de-regulation in the electric power industry progresses, the basic structures of future power system should change drastically. Particularly, in the power distribution systems which are closest to the demand side in power system, more higher flexibility and higher reliability are requested. Flexible, Reliable and Intelligent Electric eNergy Delivery System (it is called a “FRIENDS”) which was proposed by the authors is a new concept for a future power distribution system. The FRIENDS will be able to realize flexibly various requests of power customers and power suppliers.
One of the most important characteristics of the FRIENDS is that a new power improvement facilities (to be referred to as the “Quality Control Centers (QCCs)”) are considered to install very closely to the customers. However, the interior structure, the control method and protection system of the QCC are not established yet. Therefore, this paper expresses many functions to be accomplished by QCC and proposes several concrete interior structures as main parts of QCC. Further, those characteristics are explained qualitatively in this paper.

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In recent years, the introduction of Superconducting Magnetic Energy Storage System (SMES) into a power system is drawing considerable research effort because of their high efficiency rate and large storage capacity characteristics.
In this paper, the introduction of SMES into a power system and its effects on energy and on environmental issues are addressed. The analysis results show that the introduction of SMES can considerably cut down CO₂ emissions without increasing the production cost if it substitutes the operation of thermal plants during peak load period. However, to achieve this, nuclear plants are also needed for charging purposes. Thus, an algorithm to find the best generation mix, subject to CO₂ emission constraints and nuclear plant introduction constraints, is proposed.
The inclusion of nuclear plant constraints increases the coal consumption, hence CO₂ emissions. Nevertheless, in most of the analyzed cases, the introduction of SMES could attain important cost savings and environmental conservation.

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Recent steady increase of electric power demand causes power sources to be larger and further from cities. Wide area power interchange leads to make a power system larger and more complicated. The network is susceptable to poor damping power swing oscillations of relatively low frequency which influence to the whole system.
This paper describes a new developed generatot's double input signal PSS(P+ω input PSS) design method. Several power system conditions (power flow and/or power system network patterns) can be considered to satisfy a well-stabilized power system for each system condition. This method has major features as follows. (1) Weighting factor for eigen value sensitivity of oscillation mode is considered when PSS parameters are updated in a parameter optimization step.
(2) The new method provides a good result for generator local oscillation mode and inter-area mode under peak and off-peak power flow conditions.

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In power systems, power electronics apparatuses such as static var compensators (SVC) and thyristor-controlled series capacitors (TCSC) have been introduced. SVC and TCSC both consist of a thyristor-controlled reactor (TCR) in parallel with capacitor banks. By adjusting the current through the reactor with the thyristors, we can change their reactances at a fundamental frequency. However, their admittances at other frequencies are important in studies of harmonic resonance and subsynchronous resonance. The admittance of a capacitor is clear, so we study that of TCR. First, we calculate its admittance by superimposing a small voltage of a frequency on the fundamental voltage, and then extracting the current change of the frequency. The conventional theoretical equations prove to be applicable only to the fundamental and the harmonic frequencies. TCR has conductance, and it can take negative values at other frequencies. We derive a theoretical equation applicable to general frequencies. The admittance is a function of the frequency and the firing angle. For the harmonic frequencies, it also depends on the phase difference between the fundamental and superimposed voltages. Lastly, we compare it with the simulation result to show the validity of the theoretical equation.

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Global environmental problem induced by vast amount of consumption of fossil fuels is one of the most important subjects in the world. To solve this problem, utilization of solar energy is one of the most useful methods. Above all, PV system is one of the power generation systems expected to attain this purpose, which is composed of PV modules connecting many solar cells. Power generation of solar cell is affected by the fluctuation of solar radiation and temperature, and actual output is less than that of standard condition. In this paper, analytical considerations is done to obtain the maximum output of PV array under some solar conditions and we obtain maximum conditions from simplified V-I characteristics equations. From the analysis, the output increses by the method we introduced and we defined the characteristics of solar cell for this realization.

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