Metal ions generated from an impulse vacuum arc were measured by a time of flight (TOF) method. A gap between a needle cathode and a rod anode, a grid electrode made of metal mesh, a linac tube and an ion collector electrode were installed in a vacuum chamber and the gap was fired by a negative sinusoidal arc current. A negative square pulse was applied to the linac tube at an appropriate time after the arc ignition to extract a sample of ions. Pb⁺ and Pb⁺⁺ ions were measured for a lead cathode and Cu⁺, Cu⁺⁺ and Cu⁺⁺⁺ were measured for a copper cathode.
TOF ion currents were measured as a function of the ion extraction time. The duration of the sinusoidal arc was 13 μs and Pb⁺ ion currents were measured only within 49 μs after the arc ignition, while Cu⁺, Cu⁺⁺ and Cu⁺⁺⁺ ion currents were measured within 15.5 μs. The lifetime of the ions, i.e. the upper limit of the ion residence time at the space between the grid and the linac tube, was betermined from the time distance between the arc extinction and the critical time of the TOF ion detection. Based on the above definition, the lifetimes of the lead and copper ions obtained were 36 μs and 2.5 μs, respectively.

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An experiment was carried out to investigate the influence of metallic particles on vacuum breakdown characteristics. By laser scattering method, the movement of particles, the lifting voltage of particles and the velocity of impact to the opposite electrode were measured. The particles were made of pure copper, and the particle diameter was 0.1 to 300 μm. The electrodes were parallel plane, 40 mm diameter, and two sets of electrodes (pure copper and stainless steel) were examined.
Experimental results showed that breakdown voltage was reduced by the presence of metallic particles. This breakdown voltage reduction depended on the number of particles between electrodes. The effect of electrodes material on breakdown characteristics was not apparently observed. The observation results of the paticle movement showed that the lifting voltage of particles decreased with decreasing particle size. The electrical breakdown of the gap occurred that when the impact velocity of the particles at the opposite electrode exceeded the critical value. We found microparticle-induced breakdown phenomena that could explain the phenomena of long delayed restrikes that is occasionally observed in vacuum circuit breakers.

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The experimental and theoretical investigations were made on the arc instability phenomena for the silver-tungsten-carbide (Ag-WC) contacts used in low-surge vacuum circuit breakers. After the arc instabilities started, the large and high-frequency (HF) oscillations were observed, which were imposed on both the arc voltage and current waveforms. In the experiments using the test circuit with some parallel capacitances, we found that the value of the chopping current increases with an increase of the HF current related both to the parallel capacitances and to the arc instability startings. In the measurements of the chopping current values for some kinds of Ag-WC contacts, we found that the value of the chopping current decreases with a decrease of its Ag content. This tendency agreed with the results of the analysis on the initiation of the arc instability, taking account of some thermal effects of the WC component. These results show that the low chopping current characteristic of Ag-WC depends on the thermal effect of the WC component which was subjected to high temperatures by the cathode spots.

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When a high current arc discharge occurs in transmission or distribution lines, equipments in those lines are usually damaged by the arc. So, in order to grasp the damage of the equipment, the molten losses of the electrodes made of iron, copper and aluminum have been experimentally stadied in the indoor space with no wind in conditions of arc current from 1 to 60kA, arc duration fromb 0.06 to 0.4 seconds and large electrode separation with no affection by each other. Those are nearly proportional to the integrated values of arc current by time.

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The total radiated power of thermally decomposed polyethylene vapor is obtained as a function of temperature ranging from 2, 500K to 30, 000K, the pressure being 1 atm and the wavelength range being 200nm to 1, 000nm. It is calculated as the sum of radiated powers of continuum radiation, H, C⁺, C₂ and CH spectra. The calculated result indicates that (1) C₂ spectral, CH spectral and continuous radiations are dominant below 5, 500K, from 5, 500K to 12, 000K and above 12, 000K, respectively, and (2) the total radiated power takes a local maximum value and a local minimum value at 4, 500K and 7, 500K, respectively, and then increases with temperature up to 17, 000K and is almost constant above 17, 000K.
The radial distribution of the total radiated power of an arc ignited through a polyethylene tube is measured under atmospheric pressure. Using this result and a radial temperature distribution of the arc measured previously, the total radiated power is derived as a function of temperature. The calculated total radiated power agrees with the measured one around 4, 500K and around 10, 000K.

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The computational approach in which the time dependent balance equations of mass, momentum and energy are solved numerically is becoming an important technique for analyzing the current interruption phenomena of SF₆ gas circuit breaker, especially in the current zero regions. In this paper, the transport and thermodynamic properties of SF₆ gas which are necessary for this approach as basic data, are calculated under the multiply mixed condition with PTFE (-C₂F₄-) vapor as a nozzle material and Cu vapor as an electrode material. Calculation was made in the wide range of temperature from 1, 500 to 30, 000K and of pressure from 0.1 to 1.6MPa and of concentration ratio from 0 to 100%. Results showed that the magnitude of the electron density and the electrical conductivity below 8, 000K is considerably enhanced by the copper atom with a lower ionization potential, although the reduction effect by the electron attachment reaction of F atom from SF₆ and abraded PTFE vapor is considerably strong. The thermal conductivity was found to be decreased by these vapor abmixture only under heavy contaminated condition more than 10%.

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Due to a simplicity in a structure and a superiority in an interrupting performance, a puffer-type gas circuit breaker (GCB) has been widely adopted as a high voltage circuit breaker of 72kV and above rating. However, this type of GCB has an inferiority that a high driving energy is required for large interrupting capacity since a pressure rise in a puffer cylinder acts as a counter force to a driving force.
Utilizing a thermal effect of arc energy on a pressure rise is admitted to be useful for reducing a driving energy. In this paper, two types of interrupting chamber are investigated, which are self-pressure-rise type utilizing a hot gas from an arc for pressure rise without gas compression, and hybrid puffer type which compresses a hot gas introduced into a puffer cylinder. Followings were clarified from a calculation of pressure rise and an interrupting test. (1) Self-pressure-rise type without gas compression is inferior in a short-line-fault interruption, and an auxiliary mean is inevitable for obtaining a sufficient interrupting performance as a high voltage circuit breaker. (2) By a mean introducing a hot gas into a puffer cylinder, a high pressure can be effectively obtained. Since cross section of puffer cylinder can be reduced a counter force by gas compression becomes smaller, which results in a driving energy less than with a conventional puffer type interrupting chamber.

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The thermal puffer type GCB, which is expected to decrease the driving energy, has a good interrupting capability in the large current area. However, in the medium or small current area, its interrupting capability is lowered because the gas in the chamber is not sufficiently expanded and the minimum arcingtime may become longer.
To improve these properties, the authors investigated the interrupting capability of the thermal puffer method using the arc-driving coil which generates the magnetic field in the chamber. And the thermal puffer type GCB with the arc-driving coil, of medium voltage, having a good interrupting capability from large to small current areas, was successfully developed.
The investigation results are summerized as follows.
(1) The interrupting capability of the magnetic arc drive method is dependent on the chamber volume and the arc energy.
(2) Two types of the thermal puffer chamber with the driving coil are investigated. As for one type, having gas exhausting holes through the contact, its interrupting capability is dependent on the hole size, the coil shape and the chamber volume.
As for the other type, having the exhausting nozzle for expanded gas, it interrupting capability is dependent on both the magnetic drive effect and the thermal puffer effect.
(3) For getting a good interrupting capability at small current area, it is important to design the driving coil so as to generate bigger electromagnetic force just before the current zero.

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In many high voltage gas insulated switchgears (GIS), the effects of conducting particles on breaking phenomena are very serious. Some methods have been proposed for flashover voltage prediction in compressed SF₆ under alternating voltage condition, etc. In these methods, the flashover voltage is predicted by integrating an effective ionization coefficient near the tip of conducting particle. However, some assumptions are used to predict the flashover voltage under these methods.
In the present paper, a new method for flashover voltage prediction is proposed of a conducting particle with a sharp tip mingled in GIS. The tip of the particle often has only little corona stabilizing effect. It is the method for determination of new electric-field coefficient and new criterion proposed by the authors, which are named “Particle Tip Electric-field Coefficient” and “Flashover Criterion” respectively. A conducting particle in GIS is predicted to have no trouble, when the particle tip electric-field coefficient of the conducting particle is less than the flashover criterion previously obtained with an experiment. Flashover voltages of GIS including many kinds of conducting particles are determined by means of the proposed method. It can be seen that the proposed method is useful to predict the flashover voltage of GIS including conducting particles larger than 5mm length.

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Power, stations are unevenly distributed and located far from the main loads that are concentrated in a few large cities. Electric power networks are heavily loaded. One of normalization policies of power supplies is power network linkage interconnecting with different alternating frequency power sources. Reflecting rapid advances in thyristor valves, there are frequency converters. In order to achieve a economical design of insulation coordination, it needs to adopt high performance surge arresters. In this case, AC 275kV/AC 56/DC 125kV metal oxide arresters have been developed. High performance surge arresters help to realize small, lightweight, low-cost, converter and substation equipments.
But, as the applied voltage ratio (=continuous operating voltage/reference voltage) of zinc oxide elements in high performance surge arresters is high, they are inclined to absorb surge energies of frequency resonance temporary overvoltage, Therefore, it is important to watch the conditions of surge arresters on line. On the other hand, the spike current flows through the arrester across thyritors valves A-K terminals corresponding with the commutation voltage, and also arresters terminal ends are insulated from the ground. It is difficult to use a conventional current monitoring method.
This paper adopts the temperature rise of zinc oxide elements to watch the degradation and thermal runaway of surge arresters on line. The relation between the temperature rise and leakage curent of zinc oxide elements in parallel connection is obtained by tests. From these results, monitoring equipments of surge arresters in AC-DC converter stations were developed. These equipments are very useful for operation and diagnosis assistance functions of surge arresters.

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Metal oxide surge arresters (MOA) without series gaps have been installed in HVDC converter stations. The wave shapes of voltage applied to the HVDC arresters are complicated and the duty depends on its location and operating conditions of converter. So, it is necessary to have full knowledge of the electrical characteristics of the HVDC arresters. In addition, for the performance tests of the MOA in factories, the simple wave shape of equivalent testing voltage is eagerly expected, which is available more easily than actual voltage shapes.
In this paper, we have first studied the watt loss and the degradation characteristics of zinc oxide elements to actual voltage for the HVDC arresters using DC 3kV, 12-pulse converter, and next to DC voltage superimposed AC.
Through comparison of the test results for these two wave shapes, watt loss characteristics of HVDC arresters is clarified and there is no need to apply higher frequency voltage than 60Hz to simulate actual voltage of HVDC arresters. DC voltage superimposed 60Hz AC is equivalent enough for practical use, and the method is conveniently applicable to various kinds of performance tests.

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The four types of ZnO arresters with a series gap for 6kV distribution system have been operated repeatedly till 300 times by a large impulse current of 10kA, 4/10 μs, and changes of the performance characteristics of them to operation times were examined every hundredth discharge. Moreover, after they were operated one hundred times, the electrode and spacer surfaces of their gaps were observed by a scanning electron microscope and an electron probe micro-analyzer.
As a result, it was found that changes of the performance characteristics of the arresters are brought by metallic contamination on the spacer surface due to repeated discharges.

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A short-circuit fault current in a low voltage distribution line from a branch point to a house is usually reduced with time by increasing resistance of conductors due to temperature rise and also by arc voltage.
Bacause of features mentioned above, the operating time of conventional fuses may be remarkably prolonged. In order to eliminate that defect a bypass type of the quick-acting fuse has been developed.
The main results are as follows:
(1) A bypass type of the quick-acting fuses short-circuits the fault line at the branch point by utilizing the large electro-magnetic force due to the fault current.
(2) In order to protect almost low voltage distribution lines the minimum operating current of the fuses is settled to be 1, 000 A.
(3) The bypassing time of the fault line by the newly developed fuse is only 6ms and 10ms in case of a fault current of 2kA in the metallic contacting faults, and the arc short-circuit faults, respectively, those being about 1/100 in comparison with the operating time of the conventional fuses.
(4) The operating time of the new fuses is 140ms in case of the same fault current in the metallic contacting fault, which is only about 1/4 of that of the conventional fuses.

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In urban area, there are growing needs to ensure a bulk power distribution, a service reliability and an interconnection to dispersed-generators. It is effective to improve Network Distribution System for the above view. Regular Network Systems are often used for the area, but coordinations of the protection are complex as usual.
This report describes the protective coordinations of the regular network system that performs a bulk power distribution and includes dispersed-generators. The interconnections influence the coordination of substation protective relays and network protectors at the primary feeder fault. The increase of the network currents associated with the bulk network system makes the protection difficult at low-voltage grid cable fault.

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On AC electric railway, when a trouble happens in AC feeding circuit, protection is done by distance relay and AC ΔI type fault selective device to act an enormous change happens in the feeding current. Recently, with an increase in the transport capacity, feeding currents from substations increase and AC re-generative rolling stocks are increasingly adopted for rapid transportation.
Under these circumstances, loads covered by distance relays have come to be closer to the protective zone, so the protective zone has now to be reduced.
We developed a new distance relay that can cover wide zone for fault currents and narrow zone for loads of electric rolling stocks.
Protective zones are switched by detection of higher harmonics because load currents have higher harmonics but fault currents have hardly any such harmonics.
This distance relay has been introduced on narrow gauge lines after its expected ability was confirmed both in an experiment of this device alone and in its field test.

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To cope with the high rate of increase of power demand in main industrialized districts in Japan, 550 kV transmission systems, covering the districts, have been reinforced, and most of the main power plants are directly connected to the 550 kV systems. Through 550/300 kV substations, the majority of power to the districts is supplied by 300 kV systems. To limit the excess short-circuit capacity in the 300 kV systems they trend to be reconstructed as, so called, Radial Networks. In radial networks with high short-circuit capacity and relatively small number of transmission lines connected to the sub-station bus-bars, the rate of rise of TRV can be far higer than standard values.
This paper analyzes the transient recovery voltages (TRV) in such extra high voltage radialnetworks in Japan, together with the relevant stresses to circuit-breakers during fault clearings. Future system conditions have also been introduced. As the typical rate of rise of the TRV values, more than twice of the today's standard ones are probable.

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Recently, the electrical apparatus using power semiconductor devices have been available for not only industrial machines but also home appliances. However, a large amount of harmonic currents generated by them have a bad influence on the electrical power systems and equipment around.
Active filter is the apparatus to eliminate these harmful current by using switching devices. Although some methods have been already proposed, most of them have adopted the circuit based on the voltage source PWM inverter with high speed switching devices, such as IGBT. Therefore, it may be difficult to increase the capacity of the active filter.
This paper proposes an active filter using current source PWM inverter.
Even carrier frequency of about 2.5 kHz, the proposed active filter can eliminate harmonic currents of less than 13-th order in the distribution line. So it can be constructed by the bipolar transistors. Furthermore, the control circuit is quite simple.
In this paper, the circuit configuration, the control method and the performance characteristics of the proposed active filter are discussed. We will show the simulation and experimental results of the tested apparatus.

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This paper describes experimental results concerning with the effects of DC excitation of transformer core caused by geomagnetically-induced currents (GIC).
As a first step, we investigated the response to DC excitation using three different small scale core models.
The results demonstrated that a single phase three-legged core form is most susceptible to DC excitation, and that a three phase three-legged core form is not affected by DC currents.
We also fabricated large scale single phase shell and core form transformers to evaluate local heating effect caused by DC excitation, since this single phase core form is most susceptible to DC excitation. The results of these experiments showed that transformer heating levels caused by DC currents can be quantitatively estimated.

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Abnormal overvoltages were measured with a transformer for a 69kV arc furnace in the field. Waveforms of temporary overvoltages due to ferroresonance containing high-frequency components of several hundred hertz were obtained. The generation mechanism of these waveforms was clarified in this paper. The cause of the overvoltage was uneven exciting by vacuum switch of foreign manufacturer.
Transformer ferroresonance is already known. However, there have been almost no reports explaining abnormal voltage waveforms containing the high-frequency components described above.

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