Yoshihiro Murooka

Nanosecond surface discharge development using the computer simulation method

The authors have analytically studied the experimental results of the nanosecond surface discharge by using a simulation model. The results used were obtained using the dust figure technique with a nanosecond square pulse generator under the following conditions: an applied voltage of 5–20 kV, a pulse width of 3, 5, 8,..., 920 ns, and a gas pressure of 50, 100, 150,..., 760 Torr. Three kinds of simulation models were used: the first was based on the continuity equations together with the Poisson’s equation, without any photoionization effects; the second examined the gas photoionization effect on the first model; and the third considered further the photoelectric effect on the insulation surface. From a series of computations, it was found that by using the third simulation model, the experimental results such as the developing length of the corona streamer and its velocity were roughly confirmed, and the field intensity at the streamer tip was also obtained. Finally, the photoelectric emission coefficien...

3.0-ns surface discharge development

The nanosecond time‐scale developing mechanisms of positive and negative corona streamers on the insulation surface are investigated using a square pulse generator and the Lichtenberg figure technique. The developing length of the corona streamers in air is measured at a pulse duration of 3 ns, an applied voltage of 7–20 kV, and a gas pressure of 150–760 Torr. The results are compared with those obtained in the time range of 5–920 ns. The ratio of the developing length obtained at a certain pressure and that obtained at atmospheric pressure becomes a constant value irrespective of the magnitude of the applied voltage, and it increases as the gas pressure is reduced. The time lag of corona streamer inception increases with decreasing pressure. The time lag for the negative corona streamer obtained at a voltage of 20 kV is 0.1 ns at atmospheric pressure and 0.35 ns at a pressure of 150 Torr, while that for the positive corona streamer obtained at the same voltage, is 0.55 ns at the atmospheric pressure and ...

Two-dimensional optical measurement techniques based on optical birefringence effects

Some dielectric materials become birefringent when sub- jected to an external force, such as an electric field or a mechanical force. For more than a decade, our research group has been engaged in developing two-dimensional optical measurement techniques for the dy- namic measurement of charge distributions on a dielectric surface using the electro-optic Pockels effect, the dynamic measurement of electrical field distributions in a liquid using the electro-optic Kerr effect, and the measurement of birefringence vector distributions in plastic plates using the photoelastic effect. The system nonuniformity and the system reliabil- ity are the inevitable problems in two-dimensional measurement sys- tems, and make two-dimensional measurements quite different from point measurements. The common image-processing techniques that have been specially developed to overcome these problems are ana- lyzed and summarized; detailed mathematical analysis is avoided.

Theoretical studies on nanosecond surface discharge phenomena observed using Lichtenberg figure method

ContentsThe nanosecond surface discharge phenomena on the insulation plate have been studied using a Lichtenberg figure method. In the experimental setup voltages of +7 to 22kV, pressures of 150–760 Torr and pulse widths of 3–11 nsec were applied. The developing length of the positive corona streamer has been precisely measured against the applied voltage as a function of the pressure at a given pulse width.It was found that with increasing pressure there was an increase of inception voltage, while the time lag of corona streamer inception decreased. The developing velocity of charged particles on the insulation plate is discussed from a view point of a modified drift theory of charged particles. Finally, it is concluded that the detardation factor due to the photoelectric emission from the insulation plate plays a more important role in the corona streamer development than the electron collision ionization or the gas photoionization.ÜbersichtEs wurden Gleitentladungen auf Isolierstoffoberflächen im Nano-Sekunden-Zeitbereich mit der Methode der Lichtenbergschen Figuren untersucht. Experimentell wurden Spannungen von +7 bis 22 kV, Impulsbreiten von 3 bis 11 ns und Gasdrücke über dem Isolator von 150 bis 760 Torr angewendet. Die Elektrodenanordnung bestand aus einer Nadel und einer ebenen Elektrode, die mit der Isolierstoffplatte bedeckt war. Die Ausbreitungslänge der positiven Koronaentladung wurde als Funktion der Spannung bei verschiedenen Drücken und konstanter Impulsbreite gemessen.Es zeigt sich, daß sich bei zunehmendem Druck die Einsatzspannung der Koronaentladung erhöht, während sich die Verzögerungszeit vermindert. Die Ausbreitungsgeschwindigkeit der Koronaentladung auf der Isolierstoffoberfläche wird unter dem Gesichtspunkt einer modifizierten Theorie der Ladungsträgerbeweglichkeit auf der Oberfläche diskutiert. Bezüglich der Ausbreitung der Koronaentladung auf der Isolierstoffoberfläche zeigt ich, daß offensichtlich die Photoelektronenemission von der Oberfläche einen größeren Einfluß hat als Elektronenstöße und Photoionisation im Gasraum über dem Isolierstoff.

New Pockels field sensor with ferroelectric liquid-crystal phase modulator

A new optical field sensor for measuring the electric field close to an electrical discharge has been developed. The new system that uses both P- and S-polarized light-division and azimuth angle modulation methods has been devised and investigated. By using a ferroelectric liquid-crystal phase modulator instead of an azimuth angle modulator, it has been possible to eliminate noise from the optical field measurement system, specifically, the birefringence effects in a long optical fiber cable. The optical cable is used for connecting a Pockels field sensor located close to the discharge with the main system located at the ground. Furthermore, it has been possible to compensate for the sensitivity difference between two optical detectors for converting P- and S-polarized light waves to an electrical signal. From this, it is found that by using a light reflection technique, the measurable minimum field strength is reduced from 100 kV/m to 1.0 kV/m in the discharge region. If the smallest phase change in the ...

Observation of AC surface discharge dynamic behavior under various atmosphere pressure

The surface discharge dynamic behavior under various atmospheric pressures (200 mmHg-1000 mmHg) is observed by using the advanced 2-D image lock-in amplifier technique of E-O (electro-optical) Pockels effect.

Two-dimensional optical measurement techniques based on optic birefringence effects

Some dielectric materials may become birefringent when subjected to an external force, such as an electric field or a mechanical force. For more than a decade, our research group has been engaged in developing 2D optical measurement techniques for the dynamic measurement of charge distributions on a dielectric surface using the electro- optic Pockels effect, the dynamic measurement of electrical field distributions in a liquid using the electro-optic Kerr effect and the measurement of birefringence vector distributions in plastic plates using the photo-elastic effect. The common image processing techniques that are uniquely developed in our work are analyzed and summarized.