Laser induced spark discharge in atmospheric pressure of the familiar gases (N2, O2, Air) was studied by using several kind of lasers such as a N2-laser, a Ruby-laser, a Nd: glass-laser and two Dye-lasers as a basic research for a new technique of laser triggered lightning. The output level of each laser is lower than the threshold value above which gas breakdown takes place. The laser beam is introduced through a focus lens into a gas vessel in which spherical electrodes of 40 mm in diameter are settled with spacing of 10 mm. No effect of lasers on reduction of breakdown voltage in N2 gas and remarkable reduction in O2 gas and air with the laser wave lenghth shorter than 730 nm were observed. These results lead to conclude that the breakdown is promoted by electron production by photodetachment of O- ions produced in the space between electrodes to which DC voltage less than breakdown voltage is applied. Position control of breakdown path by the laser is also demonstrated.

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The quantization of free photon fields based on our new formalism is reconsidered. The creation and annihilation operators for photons are introduced. Expanding the photon fields in the plane waves, the equal-time commutation relations for the creation and annihilation operators are obtained. The number of photons and the momentum of the system are expressed by the creation and annihilation operators. The conservation of these quantities is also shown. Finally, we obtain the Hamiltonian of the system. The absence of the zero-point energy term in the Hamiltonian is found. Our conclusion is consistent with that of Barut and his co-workers.

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The voltage-time curves of flashovers along the insulating spacer in SF6 gas become flat in the time range shorter than 1μs, compared with the V-t curves in the gas space. The paper tries to give a physical interpretation to the phenomenon by studying the initiation and development of the surface discharges optically. We use a photomultiplier to detect the initiation of streamer discharge and an image converter camera to measure the speed of the leader propagation. The test sample is so arranged that the flashover starts from the triple junction. The optical measurements show that the speed and the light intensity of the leader discharge increase with the discharge initiation voltage and the steepness of the impulse wavefront. We account for the flatness of the V-t curves in the fast time region by the enhancement of the electric field at the triple junction and the increase of the propagation speed of the discharge. We propose an equation which describes the propagation speed of the discharge in the time range of switching to steep-front impulses.

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Recently, investigations of diagnostic method for determining the deteriorating conditions of an insulating material using microcomputer have been carried out. It is already known that sometimes partial discharge in a gap, such as a void in insulation or between insulation and a conductor, may lead to the deterioration of the polymer and finaly to be breakdown of the insulation system. Research is still underway to establish a diagnostic which can aid in the determination of the deteriorating condition of an insulation materials.
In this paper, a wide and flat artificial void which is bounded by thin polyethylen sheet on either side is used for experiments. The characteristics of the gaseous discharge products, are measured by the infrared spectrometer during the discharge condition. At the same time, the distribution of the discharge magnitude according to the phase angle of the applied voltage with a discharge pulse measurement system. In order to understand the relationship between the gaseouse discharge products and the discharge measurements, the correlation coefficients were calculated.
In results, the swarming pulsive micro discharge is shown clear by the measurements of the discharge magnitude distribution according to phase angle. The relation between the occurence pattern of the gaseous discharge products and the swarming pulsive micro discharge is made clear. The gaseous discharge products are correlated with seveal electrical discharge parameters.

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The electrical breakdown phenomena in mixtures of cyclohexane and carbon tetrachloride for point-to-plane electrode configuration have been investigated using a photo optical current measuring system and a 760 ns rectangular high-voltage pulse generator. Discharges from positive points generally were more intense and faster than those from negative points. The time lag was precisely measured from the prebreakdown current. The average velocity of streamer propagation is estimated from the linear relation between formative time lag and gap spacing. The propagation velocity for a negative point in cyclohexane is exceedingly increased by a small amount of carbon tetrachloride as an additive, more extremely than that for a positive point. An polarization effect and a space charge effect on ionization of liquid molecule in the prebreakdown process are proposed to account for the additive effect.

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The extinction of the partial discharge (PD) pulse has been frequently observed in an epoxy specimen with a closed void during voltage endurance tests using a CIGRE Method-II electrode. The individual discharge pulse becomes so small that the discharges cannot be detected by conventional pulse detection methods. Such discharges are known as "swarming pulsive microdischarges" (SPMD). In this paper, the SPMD characteristics are investigated by varying the frequency of the applied voltage from 0.1Hz to 240Hz. As a result, the SPMD are found to occur less frequently as the frequency is lowered. To seek this cause, one-shot voltages were repeatedly applied at constant intervals. By varying the interval from 0.02s to 100s, the PD of electrically aged specimen was measured. It was revealed that the discharge magnitude increases as the interval becomes longer. Onset of SPMD was found to depend on the preceding discharge. The results explain the reason why swarming is harder occur at lower frequency with longer discharge interval. In the conventional pulse detection, hence, it is useful to employ the very low frequency for diagnosis of machine insulation containing enclosed voids.

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Thermal expansive coefficient of insulating oil can be calculated from its density. The slopes of temperature dependence on density of insulating oils are almost equal to each other. Thermal expansive coefficient of insulating oil is related to molecular structure. Thermal expansive coefficient α is shown as following equation, α=0.047β+4.9×10-4, where β is the ratio between structural coefficient, which is sum of molecular volume on each molecular conformation, and molecular weight. Though it has been said experientially that thermal expansive coefficient of parafinic oil is larger than that of naphthenic oil, it is confirmed that this experiential thinking is true by this study.

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The permittivity reduction of insulating paper is expected to improve a dielectric strength in oilimmersed large power transformers. Using several kinds of newly developed synthetic paper with low permittivity, insulation characteristics of them are investigated under lightning impulse and AC voltage conditions by making simple coil models. In the case of AC voltage, AC partial discharge inception voltages are improved by using low permittivity synthetic paper. However in the case of lightning impulse voltages, some of the low permittivity insulating paper show the characteristic that partial discharge inception voltages are not improved. According to the still camera observation of the lightning impulse test and SEM observation of the insulating paper surface, it is found that the half lapped part of insulating paper becomes weak points of the partial discharge inception and low permittivity insulation papers with long fibers on the surface or the edge of paper give lower partial discharge inception voltages. It is cleared that not only the permittivity value of paper, but also the surface condition of the paper has an important role to get good insulation performance effectively for low permittivity paper.

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