In order to understand a number of power of system phenomena and to foresee critical conditions in system operation, such as voltage collapse, a real-time simulator able to model the dynamic behavior of large power systems has been needed for long time. The need for real-time simulations stems from the fact that in many practical situations it is desirable to test new equipment and analyze the dynamic behavior of a large power system using the actual pieces of equipment. We developed a new digital simulator based on a hypercube type massively parallel computer to achieve this objective. The new simulator features: (1) Real-time simulation of a large power system which covers transient stability through long term behavior with constant accuracy level. (2) User friendly man-machine interfaces which mimics actual operating environment and real-time data presentation on a CRT. (3) High speed digital/analog conversion interfaces which connect the digital simulator to actual equipment.

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This paper presents a new approach to optimal reactive power planning based on a genetic algorithm which is a kind of search algorithm based on the mechanics of natural selection and genetics. This algorithm can search for a global solution using multiple path and treat integer problem naturally. In the method, discrete control variables are represented as integer strings (chromosomes). Two intentional operations are proposed to improve this chromosomes in addition to conventional operations. First one is “interbreeding” which crosses preferable subsystems each other to form a better combination of control variables. Second one is “manipulation” which improves power system profiles using AI-based stochastic “If-then” rules. Since “If-then” rules are deterministicly applied in expert systems, rules should be built without any conflict. The proposed method, however, applies such “If-then” rules stochastically. The proposed method was applied to practical 51-bus and 224-bus systems to show its feasibility and capabilitys. In both systems, the method shows very good convergent characteristics to global solutions in discrete value. During this research, many global or quasi-global solutions are found. It will be worthwhile to investigate these phenomena as further works.

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The primary aim of surge arresters in power distribution lines is to protect lines and apparatus from overvoltages induced by nearby lightning strokes. For further improvement in the performance of the power distribution system, protection methods for distribution lines against direct lightning strokes must be devised. One effective measure against direct lightning strokes is to increase the number of surge arresters. However, if the lighting current is considerably large, some surge arresters will absorb a large amount of energy in excess of their withstand capability and break down, thereby leading to a line fault.
This paper reports on the energy duty of surge arresters due to direct lightning hits to overhead ground wire. Also, the failure rate of surge arresters is estimated in accordance with the calculated energy duty.

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Overhead ground wires and surge arresters have been installed to protect high voltage power distribution lines and apparatus from overvoltages induced by nearby lightning srokes. The effects of surge arresters for protection of high voltage distribution lines against direct lightning strokes have already been investigated using the digital simulation program EMTP. Regarding the protection of low voltage distribution lines from overvolages induced by lightning strokes, experimental analyses, using a scale model line, have been reported.
This paper reports on the comparison between the experimental analyses and EMTP simulation of power distribution lines, including low voltage lines, and the validity of EMTP simulation. Furthermore, this paper analyzes the overvoltages on low voltage power distribution lines against direct lightning strokes to the overhead ground wire using the digital simulation.

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International Standard in high voltage measurement handled by IEC Pub. 60-3 (1976) has been pointed out that its requirement is not sufficient in the impulse voltage measurement accuracy, especially in front-chopped impulse.
And its revisory work has been executed by IEC Technical Committee. Corresponding to this work, the unit step response of a resistive voltage divider is discussed by the comparison of the measurement with the calculation by EMTP, to establish the simulation procedure by EMTP, in this paper.
Then, this EMTP simulation is utilized for the calculation of measured voltage in the virtual impulse voltage tests (full and front-chopped), and the measurement accuracy is discussed taking into account of various time parameters of measuring system, to help understanding of the revision.

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The transient voltage due to lightning and the operations of breakers, disconnenctors, and switches travels along the power line as a traveling wave, and causes destruction of electronic devices and malfunction of communication and control system in substations. It is important to measure exactly the wave traveling along the power line, but the measurement is very difficult, because the voltage is very high and the transient waveforms are complicated extermely on account of reflections at insulators and junctions.
In this paper, a distributed constant system was introduced in consideration of the fast transients. A method was proposed, which derives the waveforms of the transient voltage traveling along the power line from the response of a single-wire line run paralell with the power line. In order to verify the method, an experimental system was introduced, which consisted of a battery with internal emf 67.5 V, a switch, a coaxial cable as a distributed constant line, and a single-wire line above a ground plane as a main line. The transient traveling waves due to the switch on closure are measured by coupling an auxiliary (another single-wire line above a ground) to the main line. The experimental and theoritical results agree very well. This method has the advantages that the transients can be measured out of contact with a power line and that forward-traveling wave can be separated from backward-traveling wave.

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The earth-return impedance and capacitance formulas of a finite parallel multiconductor with arbitrary positions have been proposed. A comparison with measured results has proved that the accuracy of the impedance formula is satisfactory. By applying the formulas, the characteristics of the finite line parameters such as a propagation constant and a characteristic impedance are investigated in comparison with those given by the conventional assumption of an infinite line. The impedance of the infinite line is greater and the capacitance is smaller than those of the finite line. The difference increases as the line length and source frequency decrease, and the height, radius and separation distance increase. Corresponding to the above, the attenuation constant and the characteristic impedance of the infinite line are greater and the propagation velocity is smaller than those of the finite line.

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The paper presents a hybrid type stability control method based on fuzzy control to improve power system stability. The proposed method consists of a speed deviation input fuzzy controller (F1), an electrical power deviation input analog type PSS (ΔP-type PSS) and a fuzzy judgement mechanism (F2). By using the membership function of the magnitude of speed deviation/acceleration of generator, the following control schemes are considered. If the magnitude is big then the supplementary stabilizing signal computed by F1 is used to damp oscillations as fast as possible, otherwise the output signal of ΔP-type PSS is used to avoid undesireable noise effect due to noisy input signal of the speed deviation of Fl. The proposed control method increases the power system stability greatly, while it is simple to implement. The effectiveness of the method is demonstrated by one machine infinite bus and multimachine model systems.

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A pulse magnet and its modulator are developed for a superconducting storage ring commissioning at Mitsubishi Electric Corp. The magnet is a window flame type one and uses a ceramic chamber with thin metallic coating for the vacuum shielding. The modulator generates a pulse current of 5.5kA and the magnetic field is up to 1, 300G. The rise time of the field should be less than 300ns in order to obtain enough injection efficiency to the storage ring.
The shielding effects of the pulse magnetic field by the vacuum chamber are estimated using a three dimensional transient analysis program. The program solves the magnetic charge on the yoke surface of the magnet using the boundary element method and the eddy currents on the vacuum chamber using the network circuits method.
The degradation of the magnetic field is measured by the search coil for different coating thickness to check the calculation results, and the results show good agreement with the calculation results. The calculation and the measurement results show the thickness should be less than 10nm when the pulse width of the field is 600ns.
The dependence of the ununiformity of the coating thickness on the shielding effects is also estimated and the requirements for the uniformity are not so strict when the thickness is less than 10nm.

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Superconducting wires for persistent current switches and AC applications have a matrix of CuNi or mixture of CuNi and Cu. CuNi has high electrical resistivity and low thermal conductivity comparing with the properties of copper. Therefore, the thermal and the electromagnetic behaviour of such wires during quench is apparently different from that of conventional copper-stabilized composites. To investigate these properties, we consider the effects of temperature gradient in radial direction of wire cross-section and the redistribution of currents at normal front in this paper. We measured longitudinal normal-zone propagation velocities of NbTi/CuNi composites wires (strands) which have different cooling condition and compared them with analytical results by the three-dimensional finite element method (the 3-D FEM) taking into account the redistribution of currents; the influence of the transverse electrical conductance on the current sharing in a composite. The analytical results agree well with experiments. From these comparisons, the mechanism of normal-zone propagation in superconducting wires with a CuNi matrix is discussed.

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The dielectric strength of highly filtrated and dehydrated oil is investigated with AC and Lightning-Impluse voltag. It is found in the wide range of cleanness that the breakdown strength is enhanced as the number of dispersed particles decreases. Scale effect of super clean oil is studied from the statistical view point. The experimental results of the scale effect are interpreted with the “weakest link theory” and the analysis on the distribution of breakdown strength. With this interpretation, the dependence of breakdown strength on the stressed oil and the electrode area is discussed as follows. In the case of impulse voltage, the dielectric strength is influenced by the stressed oil volume as well as the strength of contaminated oil. In the case of AC voltage, the dielectric strength of super clean oil depends on the electrode area. The breakdown are discussed from the breakdown initiation point of view.

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A new protection system for capacitor banks in case of short-circuiting accident is described.
A pulsed power system, which is composed of many capacitor units and closing switches, is well known for producing a controlled pulse current of high power as for the power source of plasma experimental device, etc.. According to the increase of a capacity of bank system, it becomes important to protect the whole bank system from the accident of short-circuiting in a capacitor unit.
Although some protective ideas have been proposed, these conventional ideas have not been sufficient means to absorb the energy flowing into the failure unit from other normal units. Constructing the new 1 MJ capacitor bank for plasma experimental device, we designed a protective device of new conception. The new protection system, which is able to absorb the bank energy and to suppress the short-circuiting current flowing into the failure capacitor units, overcomes the defect in former protection systems. To confirm the utility of new protection system, we made a test of protection resistor imitating the actual bank circuit. Test result showed that absorvable energy for unit ceramic resistor amounted to 1500 joule/cc. The new system is adopted to the bank system of TPE-1RM15 plasma experimental device.

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Methods of noise reduction were studied for partial discharge location on 77kV XLPE power cables in consideration that noises are a major problem in partial discharge measurement.
A noise survey was conducted at first in the field. Noise spectra showed high peaks at frequencies over 200kHz and 550kHz possibly of radio wave origin. A study on the points of noise penetration indicated that a large part of noises is induced in cable conductor by noise current flowing in the outer shielding layer.
The use of band elimination filters was tested, as a method of noise elimination, to cut high frequencies. The method tested in the filed was effective on steady noises and reduced the noise level to about one-twentieth under optimal conditions.

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